I agree with how helpful Al has been in this forum. I would like to know the difference between vermiculite and perlite. Is there a reason to use one over the other. I had bought 4 bags of perlite to use in my container mix. I now see they also have bags of vermiculite. Are they interchangeable or is there a time to use each one (such as raised beds, seed starting, etc). Just wondered if I should have picked up a bag of it.

Vermiculite is a water sponge and perlite is like small, lightweight, porous pebbles.

They are used for opposite purposes. Perlite for better drainage and vermiculite for better water retention.

As a rule I would stay away from vermiculite for any purpose unless you really need something that will add greatly to water retention. It comes at a cost though. It will clog up the mix in containers as it's small in size and even the larger grade stuff rapidly becomes tiny in size.

Perlite is great to use, some folks even start seeds in pure perlite. I haven't, but some folks who know what they are doing on this forum have grown in pure perlite.

Justaguy, that's interesting that you bring up that some people start seeds in pure perlite. I have also been very aware of this for half a year now, and have probably found almost every reference to this here at gardenweb (because of extensive keyword searches). Some people also start seeds in pure vermiculite, and others have various soil recipes. To learn more, I have been conducting extensive, side by side trials of different seed starting mediums, including pure coarse grade perlite *and* pure smaller grade perlite, and I have to say pure perlite (of either size) was easily the worst seed starting medium that I tested. (Obviously there are many worse mediums, and perlite might even be better than most, but pure vermiculite beat it hands down, perlite/peat beat it hands down, and the 1 verm, 1 perl, 2 peat recipe put it to shame. (1.1.1 was also good, but not as.) (This was across a dozen or more garden vegetable species and about three dozen tomato varieties, always at least three seeds per medium). All other variables were held constant, where temps never dropped below 40, possibly 39 degrees (crazy gulf coast), and watering was at least daily.

Also, I find it interesting that it is so widely believed that perlite is for drainage and verm is for water retention, because perlite is also obviously a great water retainer (the sfg guy quotes a very close water retaining percentage between them), and I suspect that verm drains surprisingly well for how much water it holds. (How else could it make such a surprisingly good soil, all by itself?)

What is interesting, though, is what they each seem to do when they are included (even or especially in small percentages) in soil recipes, especially for containers. They obviously help the soil drain, but they also (both) seem to trap water pockets for fine roots to grow around and into, as best suits the root. They are like little water bottles, and they seem to improve a soil remarkably, even when present in small amounts. Somewhere there is a research publication on the use of perlite on farm fields that really surprises, because (apparently) even a light dusting of perlite on a dimpled field (dimpled so that the perlite and whatever seeds are blown into the dimples by the wind) does wonders for yields.

I have to say, one of the most surprising things I read on this forum (from Al and from dozens of others, including justaguy's post above) is that vermiculite disintigrates easily. In a half year of using vermiculite in many different ways (including a couple of raised beds using mel's mix--easily the most productive raised bed soil recipe that I've ever imagined, let alone seen the results of), I have found verm to be surprisingly resilient. Even when it breaks down (i.e. even when I smush it up on purpose, to artificially age it) it still seems to retain its properties remarkably well. It strikes me that its flat layers, even when broken apart from each other, still hold water just as flat, independent sheets. In other words, they seem to act like the individual strands of peat moss act. I would love to hear about other people's experiences with it, to compare notes.

What I meant to add to the original questions was the point that tapla does *not* expect a very long useful life from container soils. Al, if you are regularly replacing used (used up?) container soils anyway, are you sure that vermiculite wouldn't make a soil recipe improvement over your various Al's mix recipes? Even if you reduced peat by the same amount that you add verm?

(Obviously, all of this is in the interest of figuring stuff out, and said and asked in the spirit of friendly, cooperative experimentation.)

Oh, because it's funny but also to reveal just what kinds of silly things I'll test, just to see for sure *how* silly they are, let me point out: pure pine bark fines makes a TERRIBLE container soil. I made a point of growing some of each of a few different varieties of peas in pure pine bark fines, and they are some of the saddest, not quite dead pea plants ever grown (and not humanely euthanized) by a gardener. Incidentally, Al's mix grows peas MUCH better than Al's mix with the perlite replaced by additional peat. Very interesting.

Hey tomatoes.or.death (love the name by the way as I love growing tomatos).

I have not grown anything in pure perlite as of yet, but last year tried pure vermiculite and hated it. The stuff held water so long it was just unimaginable. I would water the plants in peat/perlite/vermiculite mix every day or three, but the stuff in pure vermiculite would go a week or more without a watering. When I transplanted the vermiculite grown seedlings had tiny root systems compared to the rest.

I also tried some in pure turface and these did great although I had to start most via the baggie method to prevent the seeds from washing down into the turface. Don't really know how the perlite seed starters manage that aspect. Also, I find it interesting that it is so widely believed that perlite is for drainage and verm is for water retention, because perlite is also obviously a great water retainer (the sfg guy quotes a very close water retaining percentage between them), and I suspect that verm drains surprisingly well for how much water it holds. (How else could it make such a surprisingly good soil, all by itself?)

I think you are confusing raised bed gardening (SQ FT style) with container gardening. I do sq ft gardening and my raised bed mix is 1 part compost, 1 part peat, 1 part vermiculite. I appreciate the vermiculite in the raised bed for it's water retention, but it is important to understand my raised beds are open bottomed and connected to the soil. They are not containers.

Perlite and vermiculite do not hold water the same no matter what anyone says. I repeatedly read/hear sources say they do.

No need to take me at my word. Go get a bag of each and fill a small container with the same volume of each. Next take a measuring cup and fill with water and record how much water each container takes before it all starts draining out the bottom.

Next step is count the days until each is bone dry.

Vermiculite is absorbent like a paper towel and perlite is absorbent like a rock. Vermiculite soaks up water like a sponge and perlite holds onto water due to it's porosity. The two are not even remotely comparable. I have to say, one of the most surprising things I read on this forum (from Al and from dozens of others, including justaguy's post above) is that vermiculite disintigrates easily.

Not just easily, but almost instantly. Just a few waterings is all I found it to take although I confess I have never found nor used the coarse grade, just the fine and medium grades. In a half year of using vermiculite in many different ways (including a couple of raised beds using mel's mix--easily the most productive raised bed soil recipe that I've ever imagined, let alone seen the results of), I have found verm to be surprisingly resilient.

Vermiculite is awesome in a raised bed where water retention is needed. A raised bed isn't a container, the physics are entirely different. A raised bed has a bottom open to the soil which makes the bed part of the soil. I also use 1/3 vermiculite in my raised beds (I am using Mel's mix as you are). I wouldn't use Mel's mix in a container though. Different worlds. It is like comparing what works best in a lake to what works best in an aquarium. Fish can grow in either, but treat an aquarium fish like it is in a lake and it just dies. Incidentally, Al's mix grows peas MUCH better than Al's mix with the perlite replaced by additional peat. Very interesting.

I do find that interesting and wonder if your experience will repeat another year. One of the things I love about internet forums is the diversity of experience and ideas. As long as everyone remains civil the end result is everyone gets to learn something and be better off for it.

I am frankly surprised by your success with pure vermiculite for seed starting as it is the worst medium I have ever used, but I am not shocked. I have gotten used to folks doing the same thing and having different results. I would like to better understand why that is.

I hope you stick around.

justaguy, I'm so glad you noticed this thread, and felt like responding to it. (Over these last many months, you've always been in my top three or so most interesting contributors.)

Don't worry--I know all about the difference between containers and raised beds. I only mentioned the mel's mix in the raised beds because it seemed relevant. Everything else that I've talked about has been based on container gardening.

I wonder which variable it is that has made my vermiculite experience (in containers of various sizes) different from yours. I've only ever used coarse vermiculite, but I also have only used it outdoors, in a location with probably higher than average windiness / days with wind, and with gulf coast sunshine. (The lowest angle that the sun ever takes to the horizon, here, is about 34 or 35 degrees. The highest is 84 or 85.) Starting seeds outdoors in these conditions probably favors pure vermiculite over pure perlite. It would be nice to know how much, though.

Which is why I have to emphasize again: my original questions about vermiculite are obviously influenced by my higher than average need to worry about containers drying out.

If anyone has reliable numbers on the percent (or whatever) difference between water retention levels of perl. and verm., I'd love a web link. (No, I obviously don't trust the sfg guy's unsourced numbers.) Perlite obviously holds less, but I have added water to it many times (to pure perlite that is already sitting in a measured plant pot) and it is downright shocking how long it takes for that pot to finally start leaking water out its drain holes.

I would also love to see the results of water retention testing for the different materials. Weigh while dry, weigh when saturated, and then weigh each ensuing day until each is bone dry again, all in the shade and out of any wind.

I remember someone somewhere on this forum mentioning that they did this to see how much a wick really wicked out of a non-fast-draining container. That would be interesting, too. I never liked Al's way of explaining what wicks do in containers. It is very metaphorical to say that they "fool" a soil mix into thinking that the bottom is lower than it is , but it also strikes me as the wrong metaphor. Wicks are more like siphons, which steal water from the soil they are wicking, become too saturated with water at their drippy bottom, drip water because of this, and so remain constantly thirsty siphons, taking ever more water from the soil. The question is, though, how *much* do they really take, by weight, or by quantitative drop of the perched water table? I have no doubt that wicks save containers with poor container soil (I know, because they saved mine), but I'm curious how much, exactly, they helped. Even with five wicks in a 3 gallon container, I'm not sure that the wicks were worth putting in (compared to just transplanting into better draining soil).

Which reminds me, I also tested many kinds of wick fabric against each other. Rayon is obviously gold, and rayon mop flat strands were great, but the shocking winner was a polyester rayon blend. I've got the exact blend around here somewhere--I'll post it another day if anyone's curious. The testing method was to wick identical giant cups of water , to see which would empty the cup, and how quickly. I was shocked at how poor cotton or denim cotton worked. I suspect that it absorbed but didn't want to drip it away again.

I will jump in with a few thought but not stats because this is all from memory of more active seed starting days.

I used pure large and or meduim grade vermiculite for a seed starting bed for avocado and mangoes for several years in my fruit tree nursery in Hawaii. The starter bed was on the ground but layered with black plastic on the bottom with holes for drainage. The cinder underlying soil would never oversaturate so had excellent drainage. We would use about 6 to 8 inches of vermiculite to fill the beds. During the initial month or so it would hold air and water in perfect seed starting condition but as it was watered overhead and as seeds were checked twice a week for germination the compressing would slowly by the second month have the starting media loose 25 to 50 % of its height in the bed. We would have to add more media if not enough seed had sprouted or move all seed and fluff the bed back up and reset the seed if there was room. These seed have tap roots that if broken would cause us to cull the seed. So it was economically important that we keep the bed several inches deep and fluffy enough for any root that developed to be extracting with the taproot intake.
The bed itself was very productive but the vermiculite was a changing flattening and air robbing moving target so we would have to keep fluffing or adding as we went through a two to three month seed starting process to get the 1000 to 5000 trees that we would start for that cycle. We did this for several years and the end result is that it can be a very good rooting media but overhead watering and our need to pull to check seed and constantly pushing the seed back into the media caused a signifcant loss of air and with all things to do with roots the air/water relation is crucial.

I would from this experience of years ago conjecture that an earthbox that has no overhead watering should hold the more desired traits that verimulite offers but in the standard overhead watering that most of us container gardeners use will find vermiculite to loose in the air/water exchange too much of the positive traits to soon to use it and therefore the stability of Al's mix will serve more people on average far better over even a short 3 month growing window than adding any significant amounts of vermiculite would to offset the watering cycles saved.

Keeping the above in mind I do think that for certain applications vermiculite can be very useful but has serious limitations that need to be understood well before using it for a given purpose.

I later in an Hawaiian native nursery used straight perlite and various combinations of peatmoss/perlite for seed starting in flats and 4 inch tubes for several long term germination projects for very slow starting seed (one to six months. The slower the seed germination the higher the perlite ratio would go.

Gotta get to work will add more on this later if my experiences would be of use to anyone I will be glad to share more thoughts.

Happy Planting David

I too will add my thoughts!!

I look at this this way.....I live in New England where I get only 5 hours of sunlite a day and more cloudy days than sun till at least April! With this kind of enviroment and,the use of vermiculite......DEATH sentence for my indoor plants that like to dry out and do not like wet feet. Not to say fungas nats and wet containers for days on end. I can see why you all like to use vermiculite in the areas where you live since you have a problem with lots of sun and warmth, quickly driing out your pots. I would say it is all relative and depends on where you live. What works for you there might kill mine here.
We all have sucess depending where we are. zone area, and how much sun we get.
Since I am looking for less root rot, a soil that dries quicker, and less insect problems for my damp soil, doesn't it make sense that I use a mix such that of Al's in order to avoid continual damp soil, well draining and where salts do not build up overtime?
I have been using his and I have had great sucess with good drainage and no knats, and no root rot yet...Finger crossed.Lol. In fact my trees are taking off in growth.
I have always used the usaul peat, vermiculite, and, perlite, and lost a many trees because of vermiculite and loss porous space within the soil.. Just my experience.In fact, just for an experiment, I had a pot that I kept having to water almost everyday, maybe not enough of something, but threw vermiculiate in it, and it stayed constanly damp in turn killed my Palm over a 3 week period... Maybe if I lived in a climate like you where my pots were driing out faster than you can keep up with watering them, then I might consider using vermiculite to hold moister within the soil.
Anyone North of zone 7 might find that Al's mix works better than the mix your talking about with vermiculite.
Sorry, to me it just seems like common sense.
Great thread here!!! It is so good to see evryone involved on this one!1:-)
By the way, if it were not for Al, I would of givin up on All container planting for good. All this time, he folowed through with me when I needed the help to suceed to healthy plant growth and not sucumming to stupid ROOT ROT due to bad soilmixes.
Have a great day all of you. Is is fun to see all your opinions and what you come up with. Just don't be to hard on Al..LOl

thank you JAG, Tomatoes, and hitexplanter. I do have some raised beds so I appreciate all your answers. I figured there had to be a difference just didn't know what it was. I started my seeds in one of those dome things with the peat pellets. They all germinated but now I need to transplant. Thanks for the help on what mix I should transplant into. Maybe I should pick up a bag for future raised beds and maybe the 1.1.2 verm/per/peat for transplanting unless there is a better recommendation. I bought a bag of seed starter but I think it was pure peat and I had a hard time getting it wet initially. I did use left over Al's mix for two of them and they are doing well.

OK now I know why I didn't have to water my containers very often last yr. I used metro mix that is composed of 45% vermiculite. No doubt vermiculite definitely holds water.

On top of that I wanted to add 20% compost to the metro mix this yr so that I could get some microbes working to help break down the organic fertilizers.

Would it do any good to add perlite and and if so how much? If I did add perlite would it be ok to add some compost or would it get too mucked up?

metro mix components below

spag peat moss 35-45%
hort grade vermiculite 40-50%
bark ash
bark
dolomitic lime stone

The one point that needs to be made that seem to have been overlooked or omitted above is that vermiculite's water holding capacity is temporary. Once it is fully saturated, it rapidly begins to lose structural integrity and all those little water holding cells start to collapse. When they all fully collapse, it no longer has the ability to retain moisture with any significance, plus it loses any porosity it had and becomes an impediment to drainage. This may not be a huge concern in very short duration container growing situations, but it can most certainly lead to drainage issues in the long term.

And despite justaguy's endorsement (and I generally appreciate and support most all of his opinions), I'd have difficulty justifying using vermiculite in a raised bed situation either. As he noted, raised bed gardening is quite different from container gardening and the utilization of other moisture retaining materials, like compost or composted manure, will work equally well. In fact, regular additions of OM should be incorporated into raised beds, just as you would do in regular garden soils. Yes, they will decompose and eventually stop contributing to moisture retention (hence one of the needs for their routine replacement) but the vermiculite will also stop contributing to moisture retention and faster than the OM. And being an inert, non-organic material, it won't decompose. You could still eventually face the same drainage issues you would in a container situation if the vermiculite is used in any quantity. And vermiculite is just too darned expensive to use in the quantities necessary to provide much effect on a raised bed scale.

Whats OM ? Sorry gardengirl brain freeze :>) filix

Hi all,

Hitex, thank you for sharing the details of that verm. experience (and for all your other contributions on this forum--always much and many times appreciated). Its interesting that a lot of my seedlings experience with pure verm. has been with (rather gentle) hand watering from a watering jug. (It was easier to just fill up several watering jugs at once, every now and then, than to go and turn on the hose every day.) ItÂs interesting that you could see such a drop in height. In my experiences with coarse verm., I never noticed any drop in height in any container. Also, I only tested pure verm. in seedling starter soil, which was never more than 3 or maybe even 4 inches deep.

(Of course, pure verm. mix isnÂt that interesting to me. IÂm really more curious about 10 or 15% verm. mixes that are otherwise similar to AlÂs mix. IÂm especially curious what Al might have to say (now that I think about it) about pine barkÂs ability to prevent vermiculite (in small amounts) from being squished down. I remember Al talking somewhere about how pure pine bark fines resembles pure marbles or pure broken glass, in the sense that it leaves relatively stable spaces in between itself. I wonder if my experience so far with 10/15 % verm has been good largely because the pine bark makes nice, safe little homes for it to live in.)

Thanks also meyermike. It is good to see evidence that verm. is a bad idea in cold/indoor locations. Back when I lived in zone 2/3 or so, I remember thinking of verm. as quite an odd invention.

wyndell, that 1.1.2 recipe that I mentioned came from a book that I read sometime in the last 5 or 6 months. (IÂve read many in that time, so IÂm not sure IÂll ever figure out which.) What I remember is that the authors shared that recipe as a kind of kindness to the reader, because it was the winner of their career, ongoing testing of different seed starting recipes.

greengrass and everyone else who asks for advice, please forgive me from bowing out of giving any, on the grounds that I still know next to nothing. IÂm as curious about how everyone might answer as you are. The only thing that I can bring to the table is questions and my limited testing experience.

On that note, gardengal, your post is fascinating, and your comments and suggestions are very familiar to me. I would say that everything you say about compost and composted manure is widely accepted, especially here at gardenweb. In fact, *because* is was so widely accepted, I almost didnÂt test any of it out, to see if it was all really true. IÂm so glad that I did, because, across multiple raised beds, the results have been fascinating. Pure (Living Earth organic) manure-based compost seemed like it would make a great raised bed soil, all by itself (and on top of weedguard, in part to block weeds, and in part to better learn about different raised bed soil recipes). I couldnÂt have been more shocked to discover that it has been the very worst raised bed soil recipe that I have tried. All in all, no kind of vegetable seems to do well in it compared to nearly any other raised bed mix that I have tried, and for many veggies, it was just a plant killer or almost killer. It seems to hold moisture ok, but it strikes me as a terrible root obstacle (i.e. roots donÂt push through it well at all), and it also seems to breathe especially poorly. In other words, it acted a lot like clay.

To compare (just in raised beds, always lined on the bottom with weedguard), compost with perlite wasnÂt that much better, AlÂs mix (including various slight varieties of it) was noticably better, AlÂs mix with 10/15 % verm. has been much better (and seems to be winning right now among my raised bed, 2-3 foot tomato plants), and melÂs mix (of square foot gardening fame) has been astonishingly dominant. To show just how careful a lot of this testing has been, all of these things (plus a few other variations) have been tested over the last 3 or 4 months with identically started and then transplanted crops of the same vegetable. My most extensive trials have been with a romaine lettuce. The seedlings are all the exact same age, all with the same start in life, but hen transplanted to different raised bed soil recipes. The differences have been really shocking. I almost never tested melÂs mix at all. In fact, I only tested it to confidently rule it out and never use it in the future, on the basis of its not-widely-celebrated reputation. I have been shocked and amazed at melÂs mix. Compared to compost recipes, with or without perlite, and with or without weedguard, melÂs mix has grown broccoli, kale, and swiss chard that isnÂt just much bigger than same aged siblings, but as much as 3, 4 or even 5 times the plant volume. Watering is reasonably frequent, and regardless equal across beds, and all other variables is the same. Fascinating stuff. I have had to accept that melÂs mix is really amazing, even though I was quite sure it would not be.

The curious thing, though, is this odd contestant, the part verm, otherwise AlÂs mix. It has done strikingly well in 1, 3, and 7 gallon containers (across dozens of veg and fruit species), and, as IÂve just mentioned, it is even doing unexpectably well as a raised bed mix. Tomatoes especially have been loving it. (That said, younger plants are coming in, and at younger, small but now planted-in-raised-beds stages, melÂs mix might be doing the best with tomatoes, by far). Again, IÂm curious: might it be that, in small amounts, verm. does really well in the little cracks between pine bark fines?

Interesting stuff, these topics. :-)

It just occurred to me that I should explain why I would put container soils into raised beds at all. Obviously a lack of available soil would explain it, but also I have been curious about one of tapla's main suspicions about container gardening: that aeration is far more important than people realize. Well, I wonder if it is also more important than people realize in raised bed gardening? Almost everyone talks about drainage as though it was interchangable with aeration, but tapla has made me wonder if they are slightly different variables.

Also, I like to test things purely in the spirit of "don't *know* yet why I should test that. Let's test it first, and think about it afterward if any surprises come." I only tested tapla mixes and variations in raised beds just to see what would happen. I am shocked at how well it has worked, especially with the verm. component, but also just with extra portions of peat. (I have noticed Al's sometimes mentioned recipes for his raised beds, and have been intrigued with the pine bark and two kinds of peat (plus some sand) sort of recipe. Interesting how widely useful pine bark seems to be.)

In general, raised bed gardening tends to offer excellent drainage situations. It is one of the primary reasons raised beds (or berms, their less structured equivalent) are recommended in areas where soil conditions are so heavy or drainage conditions so poor, regular inground planting is difficult at best. But I'd not necessarily recommend filling with or planting into a 100% compost medium - it's a bit too rich, too moisture retentive and too prone to continued decomposition, resulting in rapid settling and eventual compaction. One typically sees recommendations of compost comprising only 25-30% of a soil mix. Lasagne gardening seems to contradict this, as it is essentially sheet composting in place, but I would guess settling and compaction would be an issue here as well and one would need to add material seasonally to maintain a consistent soil depth. I'm not familiar with the product you mention but there are all sorts of commercial bagged composts on the market, some good, others much less so. Most quality composts will have enough texture and variation in particle size that aeration should not be a concern, at least in the outset. The frequent suggestion for adding compost to loosen or lighten heavy clay soils is based on this principle.

And "OM" is organic matter, either composted (in some stage of decomposition) or not.

This is a FUN post everyone....:-)
Let me share something with you....
I have a friend that owns a horse farm....he has some piles of horse poop at least a couple of years old and just throws seed in there...He had the biggest and badest and sweetest juciest tomatoes I ever saw in my life, along with lettuce and other vegies and flowers. In particular HUGE star gazer lilies....Just in pure old horse poop...LOL..A miracle from God I guess. I call it free Gold for your plants!!lol

Then I have a coworker who has been composting for several years. He told me I could go over and grab some last summer. When I dug into it, it was DARK and very LIGHT weight!!! I dug holes in my ground because I have poor soil and filled them with just this compost!! Nothing else. I never saw water drain so well as in this stuff, and the only plants in my yard that were very vibrant and healthy were the ones that were planted in these holes!! In fact the rest I spread on top of some of my not so good soil, and it actuall looked nice . a rich color. When I watered it even on the hottest days when it dried out, it took wtaer like a sponge..NICE!! The same plants I planted in different parts of the yard with none of this compost, they looked like ......!!
No additives....No fertilizers in any of these natural Organic Matter or.."OM'.....Just plain composted horse poop and just straight compost... In fact my co-worker said he never has to fertilze his plants, just that compost and wow are his plant georgous!!Hope this helps!!
I guess results says everything!!I think I will start my own compost pile or run to a horse farm get a bunch of big bags, and use to the full.
BY the way...I have something you might want to try for any plants you want to grow like weeds!! It worked wonders for me.
Get Dehydrated Cow Manure, throw a bunch in a wheel barrel or barrell, then let it soak in water for at least 5 days, it will start to forment and get a swampy smell..Then take this wet watery mixture and dump small amounts all around your plants....Unbeleivable the way your plants react to this stuff!!! Try it and lets us all know what you think!
Mike..:-)

P.S> Do try this in containerized pots!!!!!LOL

Sooryyyyyyy...I meant to say..DO NOT try these things in Containerized Soil pots!!! WOW

hi gardengirl, It is quite apparent that you don't like vermiculite but as I stated above I already made the mistake of buying metro mix that is loaded with it. I noticed that my containers stayed wet too long last year.

I would incorporate pine bark as Al recommends but then next year I'm right back in the same position as the bark breaks down into compost. So I guess the only remedy on a permanent basis might be perlite. Does anybody think that adding perlite to a vermiculite laden medium will help or am I wasting my time and money? Maybe I should just start over. If you think perlite will work then how much should I add? Existing potting mix below. Thanks

metro mix components below

spag peat moss 35-45%
hort grade vermiculite 40-50%
bark ash
bark
dolomitic lime stone

Does anybody think that adding perlite to a vermiculite laden medium will help or am I wasting my time and money?
How did your plants do in the mix last year? If they did really well then you can probably just go 1 part perlite 2-3 parts mix and get the same results.

If your plants didn't do as well as you expected I would make a new mix. You would have to add so much perlite that you wouldn't be saving much money in the long run.

I had a difficult growing yr because it was my first try at organic gardening and my first yr at container growing. It took a while to figure out that my fertilizer was too weak for a soilless mix. My crops were fair in what many claimed was a great year for gardening.

What I noticed is that I only had to water every few days even in the middle of summer. I don't know if the vermiculite will break down even more in what will be the 3rd growing year and cause even more clogging this yr(I bot the soilless from a nursery that used it for one growing year). I also wonder if adding 25% perlite will make the mix too lite to hold a tomato plant down. Thanks for the help in trying to sort this mess out.

If the mix is in it's 3rd year it is time to toss it out or put in a ground bed, fill a low spot etc.

It's mush at this point and your stuff didn't do as well as you expected last year so, start over is my suggestion.

Try loading the mix with a controlled release fertilizer like Osmocote or similar at a rate of 1 cup per 2 cubic foot bag. This helps to ensure no shortage of the majors.

I recomend you start with Al's mix as a basis. It will require daily watering and on hot, windy days with plants that need a lot of water maybe more than once. If this won't work for you then increase the percentage of stuff that retains lots of water.

If you feel strongly that you want to grow organic in containers replace the peat with compost.

If you wish to use the same mix for a few years you will do well to keep the peat/vermiculite/organic matter to a minimum as the bark is going to compost a bit more each season, but it's a balancing act full of compromises.

That's too bad. I realized that Al might not answer any of my questions, but I was hoping he would. (I realized he might not answer because I've read an enormous volume of his posts. In fact, I suspect that I know roughly what Al's response would have been, based on other posts where he just barely responded to something, rather than saying nothing.)

I respect that, and am thankful that someone like Al spends so much time even reading all of our questions, let alone answering so many of them.

That said, I am worried that vermiculite is an under-examined topic, and I am especially worried about all of the red flags that I have noticed (on this subject in particular, but on others as well) of confirmation bias. I happen to know a great deal about confirmation bias because of my field, and I think all of us who garden (and who do just about anything empirical) would benefit enormously from reading even just the first section of:

en.wikipedia.org/wiki/Confirmation_bias

I urge everyone here at gardenweb and especially container gardeners to pay special attention to the 2-4-6 problem. Human beings, in a nutshell, are incredibly bad at testing their hypotheses. They mistakenly try to confirm them, when it would almost always be much more profitable and informative to try to disconfirm them. The problem is quite serious, and difficult to avoid. What's most curious about this problem is that "experts" in a field (who really are genuine experts) tend to be the bias's biggest victims.

Maybe vermiculite really is not even worth testing and comparing across container soil mixes. I guess I'll keep checking, as best I can, and I'll share my results as they come in. I'm not cheering for any particular result. I just want to know.

One quick, last aside: there is a flat Earth society that every now and then sends a member off on cross country skis to the north "pole", in order to snap and bring back a picture of the edge of the flat (not round) Earth. Personally I think these people are some of the most tragically mistaken people on Earth.

But I'm still very, very glad that they're checking.

Thanks again, Al, for everything. I don't think you'll ever really realize how much we all appreciate it.

I am not reading any confirmation bias on this thread. Some knowledgeable posters on this thread have given you solid reasons as well as their own experiences why vermiculite is damaging in container gardening. In the final analysys experience is the best guide. I had no idea that vermiculite broke down to such an extent and would impede drainage as early as the second growing season. Unfortunately it was my growing season and I am here to tell you that I do not like vermiculite especially the concentrated amount in my potting mix.

Thanks gardengirl and Al. Ya om organic matter. Ug I think I was back at woodstock! :) I used verm in a flower bed and it worked great. I would like to play around with it for seedlings, see what happens. filix

I tend to lean on two experiences when I garden (and read through the gardening forums):

I use to be an avid black and white photographer, and I used to belong to a forum dedicated to B&W film and their development. I noticed there were many people who loved film/developer combinations which I did not get good results from. There were probably 10 times as many people who hated the film/developer combination I use and have achieved great results from. Why? Because everything they do is different than what I do... cameras don't quite shoot the same, water is different from one region to the next, tank agitation is different, etc. etc. etc. What I also saw was a lot of people abandoning what they had learned about the film and developer combination (in search of the holy grail) for what someone else was using and getting good results with. I can't tell you how many times the question "What is the best film and developer combination?" was asked. The posts usually went something like:

person 1: I use X and love it.
person 2: I hate X, I've always used Y.
person 3: X was okay, Y was muddy, Z is what I use.
etc.

The second event, which reinforced what I had learned in the B&W forum, was at a Harris County Master Gardener's plant sale. I sat in on a discussion about growing tomatoes (ToD should appreciate this one). The perennial question was asked, "What is the best tasting tomato?" (searching for the holy grail). The presenter (said to be an expert in tomatoes, but I didn't check his credentials) basically said, "any tomato which is perfectly ripe will taste better than any other variety which is not." I'm sure if we were to search the tomato forums, we would find many discussions similar to those in the B&W forum with people listing their favorites, and not two list are alike.

ToD, you were asking why your results were so different than others. I think the answer is quite simple. It was because, as you said, "All other variables were held constant...". You experimented with a very specific set of circumstances. However, if you optimized the growing conditions for all sets of growing mixes, I would suspect your results would be different. Perhaps this is the antithesis of the 2,4,6 problem. I would suggest if it works for you, then use it. You can maximize your results by tweaking your methods.

As for my own experiences with Vermiculite. I am among the group which really doesn't care for it, but finds it is a necessary evil in some instances. When I used it in the past, I noticed a great deal of shrinkage in containers. I currently have a small container (approximately 4"d X 6"h) which the growing mix has compressed to about a third (maybe less) of its original volume. Here are some pictures from past years:

pomegranate cutting
{{gwi:8621}}

fig cutting
{{gwi:8622}}

Some of the loss can be attributed to the mix "splashing" out while being watered or during rain, but there wasn't nearly enough outside of the containers to explain this much shrinkage. Furthermore, it is evident the Vermiculite has flattened considerably, while the Perlite has held it's shape.

Many years ago, I tested coarse Vermiulite (the only grade I've used). I filled a container (same size as above) without planting anything in it. As it dried out, I watered with the gentlest stream of water I could. The container was protected so it didn't get rained on and nothing was around to fall into it or knock it over. After three months, this is what it looked like:

{{gwi:8623}}

It is about a 30% shrinkage under its own weight. Also, without exception, the cuttings I have rooted in Vermiculite based mixes have had much smaller root growth over the same period of time than those grown in my normal mix.

These are the reasons why I don't use it. In my particular situation, for my particular usage, in my backyard it doesn't behave in a suitable manner... but that's just me and my experiences. Your experience will be different (at least slightly) than mine.

BTW... my growing mix has been a combination of pine bark, expanded shale and Perlite. I have noticed very little settling with these components.

~james

What do they call expanded shale? and where can I get it?

halfNosed Jack and the Dawg

QUOTED from Tomatoes or death:

The curious thing, though, is this odd contestant, the part verm, otherwise Als mix. It has done strikingly well in 1, 3, and 7 gallon containers (across dozens of veg and fruit species), and, as Ive just mentioned, it is even doing unexpectably well as a raised bed mix. Tomatoes especially have been loving it. (That said, younger plants are coming in, and at younger, small but now planted-in-raised-beds stages, mels mix might be doing the best with tomatoes, by far). Again, Im curious: might it be that, in small amounts, verm. does really well in the little cracks between pine bark fines?

(END QUOTE)

I know this has been awhile, but I've looked through this thread and have not found - what is the actual mixture you are using for your containers? Not the seed starting mix, but this "variation of tapla's mix" that contains 10 to 15% vermiculite. What's the actual recipe?

I've been looking and can't find Tapla's mix, and I don't know what you may have reduced when adding the vermiculite.

So if you're still around, could you publish the actual recipe you are using?

Thanks.

Sojourner

You can find it at the link below, with some other reading you might find beneficial. I never refer to it as my soil or Al's mix, but I guess lots of other folks do. ;o)

Al

That's not really what I was asking for. I was hoping that Tomotoes or death could tell me how he had modified your mixture to use vermiculite. I'm not sure what he has modified.

I guess I'll try to go with some form of Mel's mix since I don't have access to his modification to yours.

Sojourner

"That's not really what I was asking for. I was hoping that Tomotoes or death could tell me how he had modified your mixture to use vermiculite. I'm not sure what he has modified."

Correction, sojourner - TOD is a "she"

My experience with vermiculite is that it is great for short-term containers (like vegetables planted on the porch for summer, rooting and seeds), but vermiculite compacts over time and changes your soil dynamics choking established roots. Peat does not change much so the established roots do not have to cope with changing soil condition as the mix settles.

Great old thread, I've noticed that all of the commericial seed starting mixes are peat/verm/lime for ph. Next year I plan on using a turface/pine barks in the bottom of 8oz cups and the top inch or so will be seed starting mix. After the first pot up seed starting mix is going bye bye.

I really had a rough time keeping all of my seedlings watered, peat really gave me trouble.

I have coarse vermiculite in my raised beds, not mels mix but about 95/2/3 home made compost/peat/verm. I'll add some fines and turface to it before next growing season.