Here's my 2 cents : general rule of thumb is to backfill tree with what came out of the hole, and to top that off with a layer of compost, and then mulch. Tree should be planted at ground level or slightly above. As someone said, recreate what is found in the forest.
The reasoning behind it is that if conditions are "too" wonderful in the hole, the roots will not want to "leave home" so to speak and will tend to circle and stay in the hole. This is probably particularly important in soils with high clay content, as roots may have trouble making the initial penetration into undisturbed soil.
If the tree is going to reach its full potential, the roots have to "leave home".

* Posted by dcsteg 5/6 KS (My Page) on
Mon, Mar 12, 07 at 10:35

Hello Pam. My take on soil amendments is this. The roots to your new panted conifer are going to jump from the planting hole to native soil in more or less then a year. So why spend your money on expensive amendments when they will have little or no value. I disagree that the root system will stay in amended soil because because there is nothing better to go to. Simply not the case.
Nurseries push amendments because there is big profit margins to be had. Save your money and go buy another conifer.
Ken on this forum grows every thing in pure sand. His planting techniqe is different but he is quite successful. Has the conifer garden to prove it.
Enjoy your sand and go plant. You will be suprised as to how well your plants will do with no amendments.

Dave

Studies have proven that root density of a variety of trees planted in clayey, sandy, and 'good' soils increases when amended with peat moss or other organic material. However, these roots stayed within the amended hole....resulting in greater problems (of many kinds) as the trees matured. Thus, it's in the best interest of your trees (in terms of long term success) that soils are NOT amended if planting hole by hole.

If, however, you are preparing an entire planting bed, and incorporating the tree within it, amending is a positive thing.

Use mulch on top of your trees' root systems to improve water holding abilitiies. At the present time, I am growing in heavy clay soil, and I add no amendments to the backfill, whatsoever. Prior to moving here, sandy soil was the norm for me.

I can think of no exceptions regarding soil type. If there is something ELSE going on with the planting site, such as a hard pan layer, poor drainage, anerobic clay, etc., then something else needs to be done; soil amendments (alone) cannot fix those problems.

hey .. my ears were burning.. lol ... thanks for the mice comments....

here is my native soil ... aka pure yellow sand
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here is a picture when the neighbor had his septic repaired
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here is a picture of the yard
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and another view
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NO AMENDMENTS... ZIP.. ZERO .. NADDA ... sand is the perfect medium for just about all trees and conifers ... for the most part they are not wetland plants ...

that said... i can barely grow an annual or perennial ... lol .... except for hosta in the shade under drip irrigation ..... here is a picture of that ...

{{gwi:662755}}

i actually plant my stuff ... this is not about hosta.. trees and conifers ... in a moat... so that i can lay down about 5 gals of water for the first year or two ... sand gets awfully water repellent in july/august .... and it doesnt soak in fast enough .... i fill this moat with 3 to 5 inches of wood chips.. which will fill in the moat as it breaks down .... by moat i mean the tree is planted at soil level ... with a lower ring around it ....

amendments are a waste of money in my yard ... in my sand.. in my humble opinion ...

god luck with yours ... ken

What you don't want is a small pocket of material of one texture sitting in a large area of another. If you think you really do have to provide something different from what you have now, bring in suitable soil and dump it on top of the existing soil, plant in that. Loosen roots and shake off or wash off potting soil or field soil when planting. Like a small liberally amended planting hole a rootball of different material will often interact unfavorably with dissimilar surrounding soil. Amended planting holes dug out of damp heavy soils may act as sumps during wet conditions. When water is less abundant amended backfills or coarse potting soils often lose water to surrounding soil. I have found many instances of this latter phenomenon myself, even digging up specimens some time after planting and plunging them in water to get the air out of the soilless potting medium. In addition, roots of plants that have been grown in containers at some point (including balled-in-burlap stock) are very often deformed.

Mulch after planting, be sure to keep moist until there has been time for plenty of rooting out.

I think location is also important to determine whether or not amending is necessary. Here in the southwest, it is necesary to add some organic material to improve water retention. I always add some peat moss as well as a thick layer of mulch. That not only increases soil water retention, but also reduces soil temperature and helps reducing water consumption. But as you said, only helpful for a couple of years, enough time to get the tree stablished
I don't believe roots will remain in the backfilled hole, that hasn't been the case for me, root extend beyond in a very short time.

osprey

Amending of backfill not being beneficial a basic phenomenon not affected by regional variables. Amending of backfill may make it more likely to shed water, rather than retain it, as it makes it more porous. Anything that makes the texture of the backfill significantly different from the surrounding soil will be likely to affect how water enters the planting hole and how it leaves the planting hole.

bboy

sorry to disappoint you, but amending does not make the soil more porous, at least not here in the southwest with a loam/clay soil. Water from irrigation drips right on top of the amended soil, and it remains moisten for longer time. I know because I never amended before, and watering had to be done very often...
As I said, it may only be true for my conditions, I don't speak for everyone

osprey

re: sorry to disappoint you, but amending does not make the soil more porous, at least not here in the southwest with a loam/clay soil

Clay soil is made of the finest soil particles, so any organic matter will consist of relatively coarse particles As a definitional matter, the amended soil would be more porous, becuase larger particles have larger pores between particles. Does that make sense?

Anyway, my two cents on amending soil is that if you are going to do it, you have to do it on a huge scale (much bigger than twice the size of the rootball). That should mitigate the problems with water movement.

Might be worth noting that, in time, amended soil will tend to become more like the native soil, because the organic material mineralizes and the charateristics of your water change the characteristics of the soil.

It sounds like you are talking about improved penetration, due to loosening of the soil. This is accomplished by the forking or tilling part of the operation. The principal benefit of peat as a soil amendment is as a soil acidifier.

"During 1973-1976, studies were conducted in Oklahoma on clay loam soils and subsoil clays. The subsoil clay site was a new housing development where all of the top soil had been removed to fill a wash and level the site. Soil fertility was very low and water penetration through the red clay was very slow. Schulte and Whitcomb used silver maple (Acer saccharinum) and Chinese pistache (Pistacia chinensis) in one study with peat, pine bark, vermiculite and sand added to a clay loam soil and a clay subsoil at proportions of 0%, 20%, and 40% by volume in a planting hole 18 inches in diameter and 12 inches deep. Mid-way through the second growing season the experiment was terminated and plants were evaluated for both top and root growth. Plants with no soil amendments were consistently larger than those with soil amendments. Pine bark at either 20% or 40% was most detrimental followed by peat, sand and vermiculite. In all cases, vermiculite was neither helpful nor detrimental to plant growth. These findings were true on the clay loam soil as well as the subsoil clay.

It is important to note that during these studies there were few, if any, visual signs of stress, deficiencies, or other problems. The plants with amended soils were simply smaller. This is probably why the practice persisted for so long unchallenged or unquestioned. If all the plants on a site received peat in the planting hole and there is no comparison without peat, all appear to be fine. It is also important to note that few plants died from the soil amendment treatments in any of the studies, thus success or failure is not at question, simply degree of success (and, of course, money spent). It is also of interest that there was no "magical" treatment to make a poor subsoil clay into a productive soil."

--Carl E. Whitcomb, Establishment and Maintenance of Landscape Plants

Here is a link that might be useful: Carl E. Whitcomb

when i moved 60 miles southwest.. within MI ... i moved from wondrous sandy loam .. gods gift to the gardener... to the pure sand ...

i moved 1500 potted perennials .. 1300 of which were the hosta ...

i filled 1 to 10 gal pots with promix... when i got here ... i had the hosta beds rotovated.. tractor mounted rototiller .. to 12 inches.. my record, with friends, was planting 370 hosta in one day ... insert hand.. scoop out sand.. tip pot and stick ball o promix into the sand ...

3 years later the hosta were declining...

medium to big hosta ... no problem... medium to tiny hosta... THE SAND WICKED ALL MOISTURE OUT OF THE PROMIX.... peat based products in sand.. are a complete waste of money IMHO .... they will dry the sand... before the sand EVER lets enough moisture get to the peat to wet it ...

if you have ever opened a brand new, sealed, dry bag of peat.. i swear i could one could float across the atlantic on it .. like a bobber in the water... before it would ever suck up water ....

just two more cents ...

oh ... i had to dig up all the smaller hosta and plant them in the sand.. to get them out of the arid peat based medium which was sucking the life out of them ... . and then add the drip irrigation .. then they took off like rockets...

ken

Hi Pam. I'm not a conifer expert, but I asked a similar question a few days ago. The advice I received was NOT to amend the soil. I'll be planting some concolor firs next month and I don't plan on adding anything extra to the planting hole. I will use a fork and shovel to loosen the soil and add several inches of mulch on top, but no amendments. I'm not planting prize-winning ornamental trees, but I figure that the concolor firs will have to learn to survive in the native soil at some point. I will water religiously this summer, but that's about it.

HTH,

MA

My concern with soil amandments is with those that add a lot of immediately available nutrients to the soil. These do not make the transplant shock less, but actually increase it. Do not put any fertilizer in the hole, unless it is a special slow release kind, and do not put any manure in the hole either.

I amend the heavy clay soil around my house for foundation plantings, but I don't just amend the planting hole, but the entire area--I dig up the soil, remove the worst of the clay clods, and mix in peat and topsoil. My shrubs are growing great guns after 5 years!

--Spruce

Those responses that stress ammending a large area, or none at all, are most in line with todays thinking. What's more beneficial in the long run, is to adopt yardcare practices that encourage the retention of organic matter on the site. Such things as mulching, using a mulching mower and chopping up fall leaves rather than removing them, etc.

IMO, one of the great follies of our culture is the enormous mounds of "yard waste" piled up at municipal garages and landfills everywhere......and in the year 2007. It really shows the enormous productivity of the land.....and the absolute squandering of same.

+oM

"The dubious practice of amending soil areas destined for permanent landscape installations has been
discussed in this column on other occasions. To summarize briefly, the problem with this practice is that
within 10 years (conservatively) the organic amendment will have decomposed; one is then left with the
original soil, which will have subsided and compacted during this time. You can see evidence of this
practice by looking at older residential lawns; the lawns slope away from sidewalks and driveways and
are inches below grade of surrounding surfaces. There is no way to incorporate additional amendment
into permanent landscapes without damaging root systems. Instead, it is easier, cheaper, and more natural
to add organic material by topdressing landscapes that are not planted and harvested on an annual basis."

Here is a link that might be useful: The Myth of Soil Amendments, Part III

I want to thank all of you. You offered thoughtful advice based on years of experience. At times, you differed in the details but overall, your advice was the same - don't bother to amend your soil for trees (shrub and perennial beds are another issue) - spend your money on trees. I'll take that advice and thank you for it.

You also gave me hope that I can grow strong, healthy beautiful trees on this land. A little more than three years ago (two months after we signed the contract on the land) Hurricane Isabel roared through and left devastation behind. We lost more than 100 trees. Those that remained were leaning and damaged. I don't think anyone on this forum wants to see photos of Desolation Point after Isabel. After three years of cleaning up, we have 5 acres of bare field with 2 gum trees, 2 lopsided hollies, and an abundance of loblolly pine seedlings.

I would like to know more about Ken's moats - do you dig the moats where the trees will live permanently? I think that must be the case. I can dig moats, no problem. It sounds like a more efficient way to deal with the problem of living on sand, especially if you want a little more variety than loblollies, gum trees, and native hollies (although I do like them).

Thanks again,
Pam

tcharles26 and bboy,

I guess I am not making my point clear. I understand that adding coarse materials (sawdust, pine bark, etc) will increase porosity of the soil. But at the same time, those organic particles will retain water within its pores. You need to understand, that in the southwest we can have more than 3 months without a single drop of rain and temps well above 80, 90 and even 100F. If you have a tree sitting at the edge of your property, no lawn irrigation, just the tree by itself, all the soil around it will suck up the water that is been provided to the tree.
I'm not an expert on tree biology, but I do know quite a bit of Geotechnical Engineering. The finer the particle the easier water will be transported by capillarity due to surface tension. Some very fine clay are capable of sucking water against gravity for more than 10m.
The only way to keep water in the root system, other than irrigating every 3rd day is amending the soil. I tell you because I have over 100 P. eldarica at home, and some of them weren't amended (pine bark, sawdust, etc). All of them are healthy, but the ones with the best growth (first couple of years) were those amended. As I said before, valid for me

osprey

Even though the poster's question appears to be answered to her satisfaction I think this is still an interesting and educational thread.

Having read all of one book about soil science I know only enought to know I know very little. But I'm picking a few bones just in case someone else thinks this is worth reading.

Ken mentioned "sand is the perfect medium for just about all trees and conifers". That cannot be right just becuase I doubt that there is a perfect soil for such a diverse group of plants. And even if you were going to come up with something perfect it would definitely have silt particles, clay particles, and organic matter. 30% sand, 30% silt, 30% clay and 10% organic matter would hardly amount to a "wetland", but certainly would be superior to 90% sand and 10% other. I know he has plenty of great confiers, but he is succeding despite the pure sand, not becuase of it. Probably becuase he just barely enough non-sand has figured out (through years of experience) what practices work best in that situation.

re: osprey's comment that organic matter retains more water than clay (at least in his situation) I'm not sure what to make of that, I've read in more than one place that no other particles retain more water than clay particles becuase they are the finest particles which therefore have the greatest amount of particle surface area per unit of volume. But could relatively dry clay pull water away from the installed plant and would organic matter help address that? I dunno. Any other thoughts from the learned forum?

The finer texture of an unamended clay around a small area of amended clay (such as a planting hole) may often result in the amended hole being a desert during dry periods, as finer soil has a greater attraction for water than coarser soil. "Coarser" and "finer" because the textures of each area relative to one another are what matter.

If you incorporate peat, bark or similar material into a large area, such as a bed then only the edges of the bed are affected by the interactions between the two textures - until the organic amendments decompose and return the soil to its original texture, at which point you have similar conditions to those which you started with before amending.

The idea that amending when planting long-term subjects like trees and shrubs is still worthwhile, even though the amendments will eventually disappear because it gives them a good start is disproved by multiple studies where the result was that the test subjects planted with amendments got a slower start than those that were not.

I think bboy has the best grasp on the issue- i have seen he studies he is refering to and can say they are sound.

bboy,

Just do the experiment, take a section of undisturbed wet clay fully sturated and a piece of pine bark (fully saturated) and leave them on you sidewalk. Then after a couple of days see which of the two is wet....... As simple as that.

osprey

Osprey, that is not a sound comparison.

The bonds that hold water to clay particles are very strong, indeed. At a certain point (in the drying process), capillarity has no effect whatsoever. However, some of that tightly held water still makes itself available to plant roots.

My property is on rock hard red clay soil. Though we've amended the large perennial beds prior to first planting, the lawn remains on pure clay, as do all of the trees that we've planted. Last summer, with months of drought and record breaking temperatures, we saw no flagging of our trees though we watered once a week only. Under normal conditions ( at least one rainy afternoon every couple of weeks), we don't water all all. We don't have an irrigation system.

Let me put it this way... here even Bermuda grass will stop growing and even die in the surface some bad years due to drought.. and it is clay. You will be surprised if you dig a hole here.. the rock hard black clay will come out in clumps like stones and no matter how hard you try to break them apart the particles, you will never succeed. So imagine what happens to the water you provide to the top..

osprey

BBoy, I'm going to have to disagree with the way you've tried to present your case here. Oddly, I actually agree on some level with what you are trying to say here. There are cases where amendment is used that it is not appropriate. But to present that one study as an example of why amendment doesn't work is ridiculous. I can tell you right now, what happened was that the organic matter sucked nitrogen out of the soil to decay, starving the trees. This is especially believable with a rank, hoggish grower like silver maple. There are tough growers in any climate including the ones in the study. The results might have been different with another kind of plant.

OTOH, people will probably go on amending the soil in perennial beds, and deep tilling/double digging, whether you or Mr. Whitcomb says it works. I can say I have seen with my own eyes that areas I amended grow healthier plants than the exact same species, 12 feet away in the same bed, unamended. Amendment can improve aeration, rain penetration (important in a climate where we actually have rain in the summer, and some choose to depend solely on it for watering) growth of healthy microbials, nutrient retention, etc. etc. etc.
This summer we had a brief dry spell. Let's compare. Areas of my bed that had composted peat and a proprietary additive I'm not going to mention now added, when I dug there, were obviously retaining moisture vs. other areas that were not. My yard is a strange mix of clay and a type of silt. Composted peat may not help, strictly speaking, "retain" moisture in a clay soil, becuase as others have noted clay retains moisture very well. But decades of anecdotal evidence are enough to convince me that it helps in other ways. Maybe it helps the moisture be more available to plants. Maybe less water runs off, therefore more penetrates. I don't know, I don't have to care. I'm saying I've been gardening for almost 20 years and amendment helps in certain circumstances, so I'll keep doing it.

This remind me of, in another forum, someone saying it was fine to fertilize BLEs in the fall. Then taking some abstract study with a with specific set of circumstances and thinking it applied to everything. Any experienced gardener will tell you they've either done this or it happened accidentally and their photinia, holly, whatever, burst into fresh growth during a warm week in November. Maybe it didn't harm the plant, maybe it did, but what's the point in doing it if there are going to be dead sprouts hanging on the plant all winter.

BTW - I agree that almost any kind of "in the hole" amended me is useless and I do NOT do this. What I do, do, is amend an ENTIRE AREA where things will be planted. When adding organic material, some think you need the tiller to literally blend the heck out of the mixture. You do not. (Some tillers even advertise their ability to do this.) You don't want a huge vein of something not like the native soil running through an area, but in a year or two the earthworms will have dispersed everything around anyhow. Also, you are right that as organic matter decays and turns to CO2, it will lower the level, so an amended area should be slightly higher than the surrounding area. However I don't believe this happens in a couple years as others have suggested. I once worked in a garden that was built in the mid 60s by a retired "country gentleman", he had "double dug" in the English manner. 25 years later digging down, the soil was STILL loamy and brownish/blackish, different from the adjacent clay. Some of this of course was from on-going amendment and plant growth in the soil.

I have horrible red clay in my yard and from what I've read in this thread amending your soil is negative but I was wondering about worms or something else like that. Can they make your soil better overall or is it only in a small area?

The Whitcomb studies are very interesting. But it is probably improper to generalize them because of the limited number of trials they are based on. The establishment of trees after transplanting is a rather complex biological problem, and there is a long list of soil-related factors that potentially affect it. The challenge is to identify the critical few factors (and possible interaction effects between them) that matter the most. I don't think that the Whitcomb studies did that.

Soil composition is important because the "plants with no soil amendments were consistently larger than those with soil amendments". The soil provides nutrition, aeration, and moisture. All three are affected by soil amendments. Why would these be optimal for an establishing tree in any particular unamended soil? And why would all amendments added to that soil result in less favorable conditions?

Soil particle size and soil porosity are important for water infiltration, draining, and "water-holding" capacity. Larger pores will dry out before smaller pores do, and a heavy clay soil surrounding a planting hole will tend to draw water away from an amended, well-draining soil in the planting hole. But doesn't this effect become important only at low moisture levels? More than half of the water associated with saturated clay soil is not available for plants because it has a much greater affinity to the small clay pores than to plant roots. So the differential of available moisture between surrounding soil and planting-hole soil might not be large. Besides, when the soil is dry enough for pore size and surface tension to become the main drivers of moisture distribution, how much of that remaining moisture is still available for the plant roots to take up?

Roots of trees don't seem to have any problems with vertical soil composition gradients. Why would a vertical transition from a planting hole to the surrounding soil be different?

Just to be clear: I don't think anyone would argue that amending soil is a bad idea just generally. The issue here is amending a planting hole when installing a tree or shrub. If you have clay soil and uniformly amend the top horizon of soil with organic matter you will definitely improve it. It doesnt matter that it degrades over time. Especially if you maintain a lawn on top of it. Because intentionally or unintentially you add more organic material on top.

RE: I have horrible red clay in my yard and from what I've read in this thread amending your soil is negative but I was wondering about worms or something else like that. Can they make your soil better overall or is it only in a small area?

better overall, but they do so by consuming organic material and distributing it across different soil horizons. So you should periodically add organic material as a top dressing.