No it doesn't matter about the mixed soil. My only concern digging the holes that deep is that the trees may settle a couple inches after planting. I'd plant them pretty high.

The soil in the hole won't be fully settled by spring and you don't want to pack it when wet.

Are you sure 12 inches, 18 max, won't be deep enough?

3' deep is a mighty deep hole.

You will end up putting a bunch of subsoil at/near the surface and pushing top soil deep in the mix. The usual recommendation is to keep they layers as is unless you have a specific purpose in mind.

And as fruitnut says, those soils will not settle over the winter. It will take a couple years to fully settle.

last note, around here if I dug my holes in fall, they would be a wet mess pretty late into spring. As well as allowing the soil to freeze deeper/further around the hole. I guess if your subsoil drains really fast it wouldn't be a problem.

My method at first was to dig a big hole, throw all the grass/sod into the bottom of the hole and then just fill it back in around the new tree (holding the tree with one hand to keep the graft where I wanted it). They all seemed to be fine with that. Sod is annoying to compost, so i figure burying it is easier.

I still think the key to good growth is that ring of bark around the trunk to keep it weed free/keep it from drying out as much.

I do that with the sod.

Seems to me that putting the sod in the bottom of the hole is just asking for your trees to settle. The normal recommendation is to dig no deeper than necessary so as to limit settling of the tree after planting.

Everyone, thx. for input. I have good control of the settling issue with backfilling in the fall and planting a bit above grade in the spring. The deep hole allows me to easily expand the hole to roughly 3' in diameter.

If the system is working for you go with it I guess.

settling aside, to me it is crazy to put my best top soil at the bottom of a 3' hole and then have predominantly subsoil around my newly planted tree.

I get that it makes it easy for you to make the hole, but Depending on your soil types I can see all sorts of problems stemming from that inversion.

Easy isn't always best.

The vast majority of the trees roots are in the top 6-12"

Unless the subsoil is really ugly, mixing it all up won't cause any problems. I think that oldryder has stated that his soil drains well. In that case the subsoil, properly fertilized, will grow trees about as well as the topsoil.

When I worked for Texas A&M we did a series of experiments where the soil was dug out to 6ft with a backhoe or trencher in plots up to 20ft by 180ft. Much of this soil had a tough, high-clay subsoil. On all soils tested yields were increased by mixing the soil. On average the yield increase was about 50% and ranged from 10% to 100%. The increase in yield persisted over more than 20 years both for dryland and irrigated crops.

Besides in this case once the tree is a few years old the mixed area, even if 3ft wide, will be a small fraction of total root volume.

In my droughty sugar sand I often wish I had the ready way to auger a narrow diameter (say 4-inch) hole down to the top of the clay lying at about six feet. I'd backfill with clay- and peat-amended soil and later dig the regular planting hole atop it. I'd like to help promote the rapid deep growth of some roots to the moist soil above the clay aquatard in order to reduce the number of years I have to water well in summer for newly planted trees. Estiblished trees on the site (including apple, pear, dogwood) show little drought stress and I assume deep roots are the reason. I'd like to try this in anyway. It may turn out that roots following the drying fronts downward are growing as fast as they can in any event and there would be no advantage. Ideally, a "pole" of wicking organic non-dense (root penetrable) fiber could be placed instead down the hole and bring some moisture up. That definitely would help.

Fruitnut,

That is a interesting study you participated in. Do you know if anything similar has been run in other locations?

Did anyone come to any conclusions as to why the increase in yield was observed? WAs there anything distinctive about the top or subsoil in that location?

Rob:

I should have pointed out that on other soils results could be different. But I think on most soils that have good drainage and thus are suited for fruit, mixing the soil won't have much if any adverse affect on growth. If the subsoil were highly acidic or otherwise adverse for crops it might take time to return the soil to production after mixing.

The results I mentioned were on soil types I grew fruit on for 30 years. Drainage was moderate to slow but had no adverse affect on fruit trees that I could ever see. But if I could have mixed the soil to 6ft before planting I would have done it. And this with a dense clay at 8-36 inches and whitish calcium carbonate below that. The topsoil looked much better than the subsoil.

Yield increase was mainly due to deeper rooting and therefore greater water extraction from the soil. Tested crops were corn, sorghum, wheat, sugar beet, cotton, and sunflower.

It is not generally a good idea to dig a hole deeper than you are planting it as trees tend to sink over time when soil is broken up below the roots or root ball. Here's something that might be helpful. It's interesting that in hard pan soils it is now considered important to create a hole without steep sides, instead creating a hole like the kind of bowl that easily spills soup.

http://cmg.colostate.edu/gardennotes/633.pdf

I went back and read everything written here and thought I should add a couple of my own opinions. I don't think Fruitnut's experiment had anything to do with the efficacy of mixing top soil with sub soil. I believe what the research showed was that breaking up the soil well beyond the root ball is often very helpful in allowing fresh root to establish in looser and better aerated soil.

I believe that it is usually better to leave the top soil on top and subsoil below, which is the natural order of the forest- a parfait of textures that starts with leaves and other tree parts followed by rotted leaves, wood and bark, followed by a thin layer of black humus followed by a shallow, dark, highly organic layer. After this the soil becomes rapidly more mineral (unlike deeper prarie soils with their more homogeneous profile) so the trees have the majority of their fine roots in the upper several inches.

I think you should put the dark topsoil aside and then dig the holes placing that stuff back where it was when you finish.

I'm not sure that you are correct to call you subsoil clay-sand. Soils are a combination of different shaped particles and a clay soil is mostly fine particles but generally have some silt and sand- it's all about ratio.

I've noticed that people tend to call subsoils clay whether they are mostly clay or silt or sand. If you haven't gotten your hands in many soil types it's a good idea to find out what your soils texture really is through an easy test which you can probably find on the internet.

harvestman's post is very good information. No natural soil is pure sand or clay. Every soil is some combination of clay/sand and silt,often with rocks of various sizes. Many home tests are available allowing the gardener to find the proportions of each in his soil. Most of us prefer not to make additions of any of the components to change the soil texture, but think it is better to plant into native soil, and over time with the regular use of mulches, improve the soil from the top down as nature does. Al

everyone's opinions make great points. but sometimes we have a tendency to over do or over think the process. when i was much younger and was going to plant a tree, shrub or bush of some kind i would always dig the hole deeper and wider. then i added compost, peat moss to enrich the soil. and what i found out from my personal experience is digging the hole any deeper or wider then needed is only making you work harder for minimal gain. roots will find their way in what ever soil you have unless its solid rock. the main thing is to plant the tree at the proper height and to test the soil to see if you need to add anything. don't over fertilize and don't let the soil to dry out the first couple of years. that's my 2 cents about planting. to me that's the easy part, the hard part is finding the right trees and root stock. that's the part where i get lost.

luke

Luke, maybe you should have tried following researched methods instead of giving up on anything that might accelerate establishment. In most soils trees will grow more quickly if you loosen the soil outward about 3 times the diameter of the root ball. It's not over thinking to check out controlled studies and modifying your methods accordingly.

It's not that hard to loosen the soil further out in most soils and when it is hard that's when it's most important to do so.

Putting peat moss and compost in a hole, especially one that's deeper than a trees roots, has been shown to be the wrong way to go, so no wonder you found no advantage.

Soils differ; so do situations. While there are some good rules of thumb, they are ruleS, plural.

I have poor deep droughty sand at a planting site about 25 miles away. There is also widespread experience from a vast area of similar soil in the SEUS (not nearly all of SEUS, but a lot of it).

A larger or deeper hole and a moderate amount of amending the backfill soil with water-holding or more nutritive materials appears to have benefit and appears to have little or no or only rare negative effect, especially if the backfill soil is firmed.

In my own case the principal benefit is in holding some soil water for new plantings in between my occasional watering trips in blazing, often rainless weeks in summer. Nutrient leaching is also presumably reduced. The plants get off to a better start. In a few years there is probably little remaining physical effect (except for persistent river-valley silt or vermiculate amended into backfill soils for the finicky pawpaw).

My loose soil needs no loosening beyond the minimal planting hole; it would be a waste of effort.

Now if I were lucky enough to have a clayey soil, then a loose amended planting-hole backfill would be asling for trouble in rainy periods ("bathtub effect") and loosening beyond the immediate planting hole would have good effect.

I personally like putting in the better (in my case, only slightly better) A-horizon soil first (lowest) because my mulching and fertilizing will eventually produce another enriched zone in the poorer soil placed at top. If, perchance, it also encourages initial downward growth of roots in my deep dry sands, so much the better.

Harvestman: "a parfait of textures" thats downright poetic!!

Given the commentary I will add additional topsoil to the mix when I plant the bareroot trees next spring to replace what was lost when I dropped the sod into the hole.

(One of my challenges is pocket gophers which are a huge nuisance but have the one redeeming attribute that they create nice, big, loose piles of topsoil which can be easily scooped up for use as planting soil.)

I understand the negatives of the deep hole. I'm willing to accept those negatives in the interest creating a wide, bowl shaped hole of loosened soil for the new trees.

I'll probably plant a few trees without adding topsoil to the mix and see if I can tell a difference a couple of years down the road.

Everyone, thx for comment and input.

Guidelines are only broadly brushed pictures and the details can vary from site to site. As long as you understand the issues I'm sure you will adapt. In the past I often dug holes much deeper than the root ball in severely compacted soils and will still do it every time if there's a plow pan. As long as you don't let the trees sink below the graft union all will be just fine.