I use two different mixes. One is approximately a 5:1:1 ratio of partially composted pine bark:peat:perlite + a small amount of dolomitic lime. The other is equal parts by volume of screened uncomposted pine or fir bark, screened Turface, and crushed granite + a small amount of gypsum. Both work exceedingly well because of the high degree of aeration they retain many times longer than peat/compost/coir-based soils. Which mix are we talking about?

A picture of a variation of the 5:1:1 mix for raised beds, with some fine ingredients included that I wouldn't use in a container soil:

{{gwi:871}}

You can see how rich the soil is, and the tilth. It is also teaming with soil life.

The gritty mix:

{{gwi:1295}}

Al

Al,

Thanks for the reply!

Can you tell me the density of both mixes? (The raised bed and the container mix.)

Does the container mix work well for fruit trees, fruiting bushes and grape vines?

Does the raised bed mixture work well for these?

Does the raised bed mix need to be periodically tossed out and replaced? If so, how often and can its useful life be extended by periodically adding amendments?

Does the container mix need to be periodically tossed out and replaced? If so, how often and can its useful life be extended by periodically adding amendments?

Thanks!

"Can you tell me the density of both mixes? (The raised bed and the container mix?"

The gritty mix weighs about 8 lbs per gallon at container capacity (fully wet) and the 5:1:1 mix weighs about 6 lbs per gallon at container capacity.

"Does the container mix work well for fruit trees, fruiting bushes and grape vines?"

Yes - very well, but I prefer the gritty mix for all long term plantings (all my woody material, houseplants, cacti, succulents). I consider long term plantings those that will be in the same soil for 2 or more growth cycles.

"Does the raised bed mixture work well for these?"

Yes - very well if it's used in raised beds, but it's not suitable for containers because of the volume of fine particulates it contains. The soil would hold too much water in containers.

"Does the raised bed mix need to be periodically tossed out and replaced? If so, how often and can its useful life be extended by periodically adding amendments?"

It can be used in raised beds indefinitely if you continually replace shrinkage due to breakdown of the organic fraction with additional pine bark, compost, reed/sedge peat .....

"Does the container mix need to be periodically tossed out and replaced? If so, how often and can its useful life be extended by periodically adding amendments?"

I'm not being smart when I say you can do as you please with used soils. I don't reuse them, choosing instead to turn them into the gardens, raised beds, or compost pile. If you wanted to reuse the 5:1:1 mix, I would suggest you add additional pine bark and perlite so your new mix would be 5:2:1, pine bark:old soil:perlite. Even though the 5:1:1 mix will retain its structure at least 4-5 times longer than peat/compost/coir-based soils used in comparable conditions, it still works better if you replace or refresh it as described each year or every other year. The gritty mix retains its structure indefinitely, with the plants becoming root bound long before there would be any danger of any significant structural collapse of the soil.

Al

Al,

Thanks for the information. I appreciate it!

Some more questions:

Do you have a formula for adjusting the pH to different levels? (For example, blueberries prefer an acidic soil. Do you have guidelines for how much of what to add per gallon of your two mixes to achieve a particular pH, such as 5.5?)

Do you have any opinion on putting the 5:1:1 mix in a large (e.g. 20 gallon or bigger) SmartPot (www.smartpots.com)?

My reason for being interested in this is that I'm thinking of putting some fruit trees in large containers for a year or so until I'm ready to give them a permanent place in the yard. (We're redoing the yard quite dramatically.) The 5:1:1 mix is significantly lighter than the gritty mix, which will make it easier to move the containers around, which is an important consideration.

SmartPots are quite different than regular containers as the entire container is made from a fabric that lets air and water pass through it. For this reason, I'm thinking that retaining too much water in the mix may not be a problem if I use a SmartPot.

Something else I'm not clear on: How do the plants get enough nutrients (e.g. minerals)? Do they get it from breakdown of organic materials in the mix (e.g. pine bark fines) or do you add fertilizer, compost or something else like that periodically?

Thanks!

"Do you have a formula for adjusting the pH to different levels? (For example, blueberries prefer an acidic soil. Do you have guidelines for how much of what to add per gallon of your two mixes to achieve a particular pH, such as 5.5?)"

No formula. You'll find it pretty frustrating to chase a particular pH for container culture

In short, container media have a higher CEC than mineral soils on a bulk density to bulk density (weight to weight) ratio, but because the bulk density of container media is usually only a fraction of that of mineral soils, the CEC and buffering capacity ends up being much lower on a per volume basis. Since the buffering capacity of container media is so low, container media pH has much less affect on the pH of the soil solution than does mineral soil pH. Zzzzzzzz?. ;o)

Without very frequent testing, and the ability to inject the proper choice of acidic or basic fertilizer compounds (based on water analysis), there is no way for hobby growers to control pH to even within a whole point (5.0 - 6.0, e.g.). The pH of container media varies substantially with moisture content, fertility, temperature, fertilizer choice, ....... even the type of plant material influences pH.

.... which is why I don't bother much with media pH - only to get it in a favorable range. When you find a conventional container grower that says "I maintain my pH at ____", be suspect - especially if it's lower than 6.0.

Do you have any opinion on putting the 5:1:1 mix in a large (e.g. 20 gallon or bigger) SmartPot?"

The 5:1:1 mix will work very well in conjunction with these pots. You may wish to add an extra part of peat if you decide to use them - for added water retention. You could also incorporate 1 part of calcined diatomaceous earth. This is available as 'Floor-Dry' from NAPA auto parts stores. I think the part # is 8822. Bark breaks down at a fraction of the rate of peat under the same conditions (1'4-15 the rate), so bark based media will remain structurally sound and serviceable much longer than peat/compost/coir-based media.

"How do the plants get enough nutrients (e.g. minerals)?"

On a scale of 1-10, with 1 being growing in the garden and 10 being hydroponics, container culture is about a 7 or 8 - much closer to hydroponics than growing in the garden. You can't rely on the media alone to supply your plants nutritional needs. You'll need to use a chemical fertilizer or organic soil amendments. Being very results oriented, and not being limited by any particular ideology when it comes to container culture, I find that using well aerated and structurally durable soils combined with soluble fertilizers offers better results with fewer problems and a much wider margin for error, so it's an easy decision for me. It's also the reason that I limit the total amount of peat/compost in the 5:1:1 mix to 15% or less. It makes no sense to purposely build a soil from larger particles (bark) to reap the benefits of better aeration, then add enough fine material to undo your efforts. ;o)

I maintain some 300 trees and woody plants in containers(bonsai practitioner), as well as another 100 or so miscellaneous containers with veggies and other pretty stuff scattered through the gardens & over the decks. I use (almost exclusively) Foliage-Pro 9-3-6 soluble fertilizer; but I formerly used, and sometimes still do use MG 24-8-16 All-Purpose fertilizer or 30-10-10, depending on the application.

Al

Al,

Thanks for the additional info! I appreciate it.

If you have the time, here are some more questions I would love your help with:

1. Since controlling pH is evidently tricky, what do you recommend doing for plants that like acidic soil (e.g. blueberries, strawberries)? Should I just plant them and not worry about it unless they show signs of stress? Skip the dolomitic lime?

2. With the 5:1:1 mix, how much dolomitic lime should I use per gallon (or cubic foot or whatever) of the mix?

3. If I get what are described as "pine bark fines" for the 5:1:1 mix, is that okay? Or do I need to dump them somewhere in the yard and let them partially compost for a couple of months before using them?

4. Regarding your second answer, am I understanding correctly that I could go with 5:2:1:1 pine bark:peat:perlite:calcined diamtomaceous earth or 5:1:1:1:1 pine bark:peat:perlite:calcined diamtomaceous earth:compost?

5. Related to question #4, what is the purpose of adding calcined diatomaceous earth? Is it add minerals for the plants to use?

6. Am I correct in understanding that this mix is designed both to allow aeration of the roots and to retain a certain amount of water for the plants to have available to them? Generally speaking, how long should I expect this mix to retain sufficient water for the plants in between rainfall or watering?

Thanks!

1) Nothing. If you're concerned, add gyp[sum to your soil when you make it (as a Ca source) and then include a small amount of Epsom salts in the fertilizer solution when you fertilize.

2) If you use lime (or gypsum), use 1 tbsp/gallon of medium or 1/2 cup/cu ft.

3) You an use uncomposted bark if you wish. I've used it when I couldn't get partially composted bark and it still works great.

4) I would try to limit peat/compost/coir combined, to 15% or less of the medium.

5) You expressed concern about water retention. The calcined DE would hold lots of water internally, but the particle size is large enough that it wouldn't contribute to the ht of the PWT. In most cases, it would actually reduce the ht of the PWT.

6) Both the 5:1:1 soils are designed with durability and aeration as their cornerstones. There is no way for me to tell you how often you'll have to water because the soils are different; weather varies; the difference between water use of immature plantings vs mature plantings is often very significant, and water usage in different plant material varies significantly. I will say that these soils need watering more frequently than heavier, out-of-the-bag soils, which is the price paid for the increased aeration, increased margin for error, and increased plant vitality. Both soils make excellent environments for healthy roots - a requirement for healthy, vital plants. I wouldn't be too far off if I said you should expect to water twice as often as you would when using soils like MG or Jungle-Grow.

I am never bashful about pointing to the fact that good vitality (in your plants) and grower convenience, are more often than not, mutually exclusive. Anyone would have considerable difficulty mounting an argument that these soils are not easier to grow in in every way, other than watering frequency.

I wish you well. ;o)

Al

Thanks again, Al!

A few more things and then I've probably got it figured out. (What can I say? I'm an engineer and like to understand very specifically what it is that I'm supposed to do.)

Regarding limiting peat/compost/coir to less than 15% of the total mix, can I basically substitute these for each other at will? For example, if I skip peat and coir and use only compost (in addition to the pine bark fines and perlite, of course), is that likely to prove satisfactory?

What is the "ht of the PWT?" (I have no idea what that means.)

In one of your comments, you said: "You expressed concern about water retention." Let me clarify: I wasn't trying to imply that there would be either too much water retention or not enough; I was just trying to get a sense of the properties of the mix.

Although we get around 50 inches of rain here fairly evenly distributed throughout the year and normally without a lot of variability from one year to the next, we recently had a multi-year drought that was easily the worst in our recorded regional history and was immediately followed (quite literally it was as if someone had suddenly flipped a switch) by one of the wettest year and a half periods ever. This has given me renewed respect for the drought and flood potential in this area.

I wasn't concerned that the mix might retain too much water or not retain enough; instead, I was just trying to figure out how much attention I should pay to it when we go through dry spells, for example.

On a related subject, does the mix have any wicking properties or anything like that? For example, suppose I have a container filled with the 5:1:1 mix (or some variant thereof) and the bottom third of the container sits in a shallow hole in the ground. If the ground is wet, will the moisture have any significant tendency to rise through the mix and cause part or all of the upper two-thirds of the mix to become moist? If so, can you give me some idea of to what extent this is likely to occur?

I realize the last question is fairly detailed and you may not have a good answer for me. My reason for asking has to do with finding a good way to make sure the plants get sufficient moisture (without getting too wet all the time). Right now I'm thinking through an idea related to using containers partially buried in soil that tends to stay damp due to collection of water as part of drainage patterns when it rains.

Long term, what I'd like to have is an automatic irrigation / sprinkler system for use during dry spells.

Thanks!

"Regarding limiting peat/compost/coir to less than 15% of the total mix, can I basically substitute these for each other at will? For example, if I skip peat and coir and use only compost (in addition to the pine bark fines and perlite, of course), is that likely to prove satisfactory?"

I usually use peat in my soils because compost offers nothing I can't get from fertilizers and micronutrient supplements, either soluble or organic. That way, I can save the compost for the gardens. I go through a LOT of container soil in a year, so it's not unusual for me to use 8-10 cu ft of peat. Compost would do about the same job as peat, but I would try to be sure the compost is finished, or you might notice a considerable amount of N immobilization.

FWIW, I've tested coir and CHCs in soils, growing a number of plants side by side with pine bark and peat, and in every case I was wholly unsatisfied with the results of the former. I was careful to keep at least loose controls in place. I fertilized at the same time and watered on an 'as needed' basis. The plants were the same genetic material as well.

"What is the "ht of the PWT?" (I have no idea what that means.)"

Water retention is linearly related to soil particle size. As particle size deceases, water retention increases. Heavy soils, those soils of fine particulates can have capillary attraction that is greater than gravitational flow potential. That is to say the soil is able to hold on to the soil more tightly than the force of gravity. Water 'perches' above the bottom of the container. Many out-of-the-bag soils have PWTs in excess of 4". This means that if you use one of these soils in a 4" deep container and fully saturate the soil, it will not drain; rather, it will remain 100% saturated until the plant uses the water or it evaporates. If you only water in small sips to avoid the root rot that often accompanies these saturated soils, you are forced to deal with the accumulation of soluble salts that occurs when you can't regularly flush the soil.

"On a related subject, does the mix have any wicking properties or anything like that? For example, suppose I have a container filled with the 5:1:1 mix (or some variant thereof) and the bottom third of the container sits in a shallow hole in the ground. If the ground is wet, will the moisture have any significant tendency to rise through the mix and cause part or all of the upper two-thirds of the mix to become moist? If so, can you give me some idea of to what extent this is likely to occur?"

Water does diffuse through the soil in vapor form to some degree, but whether it will be enough depends on several variables. If you partially sink a pot with several drain holes into the ground in spring, the plant will grow roots through the holes and not require any more water than their counter parts planted out. On the other hand, you can't take a plant and set it in the ground in the middle of a summer drought and expect it to take care of itself.

I have friends that have taken long leaves from this country and sunk their bonsai and nursery plants they were training as potential bonsai into the ground and left them unattended for sometimes several years with no problems other than having to sort out the root mess when they picked up where they took off.

The short answer is 'it depends', but use your reasoning to make good decisions. It's unlikely you would have any problems with over-0watering, unless the soil you sunk the pots into was heavy clay. In that case, the bathtub effect that would be created could be a considerable pain in your ..... side.

"I realize the last question is fairly detailed and you may not have a good answer for me."

Oh ye of little faith. ;o)

Al