westelle:

All current research shows that digging a hole 2-3x as wide as the rootball (or can) and only slightly deeper and, most importantly, using no amendment is the best way to get a new plant established.

This is contrary to almost universal belief and teachings. And leads to a lot of controversy (as I'm sure will happen in this forum under this post).

The originator of the first research along these lines was Dr. Carl Whitcomb at Oklahoma State University. Planting hundreds of trees and shrubs in holes with varying amounts of amendment (% by volume), he discovered that plants grown in the "control" (native soil with zero amendment) did better in the long run than all the others. Further research at other universities found the same thing. Soil type wasn't a factor.

Additional research showed that trees (and other plants) placed in a hole that is dug only slightly deeper were less likely to settle and have their crowns buried by soil that rotted them.

But we still find that when you dig a hole much wider then the original rootball, you do better encourage the lateral roots -- those that grow first with a newly planted plant.

Some native plant purists believe that the hole should be dug only as big as the root ball. This works when the soil is not compacted as usually is in a garden situation.

I started in the nursery industry in 1970 and the "$50 hole for a $5 plant" practice was drilled into me, both at the nursery and in my first years of hort school. It took me a while to "see the light".

The reason why the amendment concept won't go away is because there is way too much money in it for an entire industry. And because the hort/landscape industry is a very conservative industry.

Joe

Digging the hole larger in diameter allows the breaking up of compacted soil. If the original soil is used to backfill without adding amendments I can agree. Digging the hole deeper than the rootball, ANY deeper I can not agree. Planting from a container the tree is often too deep in the container and the soil should be removed till the top of the roots is found and when the tree is planted the top of the roots should be even with the soil top. Planting a bare root tree the same depth of planting and restraint on the use of any fertilizer or amendments applies. Mulch should be used at planting for weed control and moisture conservation. Al

Thanks Al for reminding me about mulching.

I tell all my students and clients to buy the bag of "amendment" when the nurseryperson sells it to them, recommending they use it to "amend" the soil. I tell my students and clients to use that "amendment" as mulch -- on top of the soil after planting.

Not only is a mulch good for weed control and moisture conservation, it also maintains a uniform soil temp, it reduces erosion (especially important when you've built a berm), and, most importantly, as it breaks down, it releases nutrients and humic substances into the soil that help develop a better soil texture and activate better root growth.

Joe

Yikes! I can remember when it was a "Ten-dollar hole for a one-dollar plant". That's a lot of inflation.

Well, this was a 5'x5' 6-in-1 espaliered Apple tree in a 24 " box that was a gift from our son, so I imagine that it was worth a good bit more than even $100.

Joe: the workmen used a lot of what they called compost mixed into the fill. It looked like a lot of aged ground-up wood to me. Do you think I should remove all this mixed fill and add back in native soil? I won't need to remove much since the hole wasn't very much larger.

Al: I always do as you suggested and dig the hole larger just to loosen our hard soil.... which, of course, is like butter right now after all this lovely rain.

westelle:

I can't imagine any practical way of picking out the mixed-in compost.

Joe

Joe: LOL What a vision.

I wouldn't pick it out, just replace it with nearby soil.

westelle you did not say how big a hole they dug to plant your tree? You will probably be OK but I would be careful when watering this first year that you apply the water on top of the original root. A small trickle that will water the original roots before running down the interface between the old roots and the new looser added mix. The normal furrow used for watering a new tree might cause all the water to disappear down the interface. Your son sounds like one of mine that sends me gift certificates so often I get behind on using them! Al

The benifits of loosening the soil are evident on newly hydroseeded lawns. Wherever the ground was dug up, either sprinkler line trenches or around trees, the grass is green and vigorous. The rest of the lawn is yellowish and stunted because the frequent watering establishment schedule leaches nutrients out.

I quit planting big trees because of all the organic material in the potting mix they come in, too much for me to hose off the roots before planting. This summer I saw a nice big apple tree (15 gal.) for only $45, and against my better judgement planted it. Sure enough, as soon as it went in the ground it started dying, no doubt from root rot. The decaying organic material no longer had access to oxygen, and used up all of it underground, rotting the roots. Now I have to pull this huge rootball out of the ground, something I'll have to use block and tackle for. Aauugh!

When planting trees, hose off all the non-organic material from the roots (this will allow you to straighten crooked ones also) and bury it in just plain dirt. Like Joe said, put all that amendment the nursery sells you on top of the ground around the tree. If you already have organics mixed in with the backfill, the best you can hope for is the roots to outgrow this toxic hole and hope your tree came with a 1-year warranty. But some nurseries I know will void the warranty if any manure was mixed in the backfill.

Guys, I am SO confused now! I have terrible, terrible hard clay soil all over my garden. Are you telling me my new plantings would be better off without any organig material added at planting time? Even in a bad soil case?

I am planting a dwarf Royal Poincianna this weekend and I need to know what to do....

I think the message here, and from gardeners in-the-know everywhere, is that you should dig a hole only as deep but wider than the root ball of the tree you are going to plant. Put the plant in the hole so that it sits at the proper elevation relative to the ground surface after refilling the hole - most trees have the top of the root ball at or only slightly below the ground surface if properly planted. Refill the hole with the same soil you removed, water thoroughly, and mulch within at least a five foot radius around the tree trunk. Use an organic mulch like shredded bark, or even better rotted wood chips.

The general feeling is that adding organic matter to the soil used to refill the hole does not benefit the tree. First, it creates a place where water can collect and saturate the soil around the roots. Imagine a bucket (the hole) filled with sand (the amended soil) and that explains how the water could accumulate. If you pour water over a bucket of sand, a lot of the water will get into the sand, but be held in the bucket, creating an underground puddle in which your tree would be sitting. To make this worse, the organic matter in the soil will decompose, removing oxygen from the soil that cannot be easily replaced if the ground is saturated. Oxygen depletion, not simply saturation with water, is what smothers plant roots.

Yes, I usually dig a hole that as deep as but wider than the root ball... But, what I have been doing so far is to mix about 1/3 compost and 2/3 original soil to backfill the planting hole.
So what I hear from you is I should instead backfill with original soil ONLY and then mulch around? The garden soil just seems so hard and dry! ...

Wow, I'm glad I read this thread because I've been doing the wrong thing for years... Well not always because half the time I forget the amendments or I'm just too lazy.

Does this also apply to potting soil or just manure and compost?

What about material that's inert like pumice or perlite? I've been adding that to some holes to improve drainage in the soil around here, which is like Play-Doh.

The Nursery where I have been getting my trees recommends that I do dig a big deeper that the root ball and then put the same soil back in so the rootball is level with the ground level. We have alot of rock and shale and need to give the roots some room to get started. They said it is better NOT to get rid of all the rocks, as they help with drainage in our heavy clay soil. So far..so good. I also dig the width about 2x the size of the rootball, I found it is easier to effectively backfill with more room around the rootball. Of course I don't buy bigger that 5 G trees.. Had enough as it is sometimes just digging a hole that size in our soil.
Anyway, I have found that talking to "MY" nursery has been very helpful. They know the surrounding conditions.

I always thought rocks made drainage worse...water doesn't drain thru rocks!

....... but rocks do allow the water to move around them creating a new channel for the water to run away.

organic stuff mixed deep in soggy warm clay may go sour.
pretty much as ladyslipper writes above...
the natural layers in mulch will create best soil conditions. (however there are plants that are native to low-organic situations)

btw, i think no "rule" will cover all species (or planting sizes) in all soils. if you're planting in nonnative conditions (soil, season length, precip distribution, etc), you could consider how you may want to compensate for differences.
soil particles need to be of similar size for drainage benefit. relatively huge "particles" (like rocks in clay) are just dead zones (a pitb to dig thru, and possibly root obstacles).
you can look up "structural soil" where (i'm pretty sure that) the rock is the most common constituent, and the nutrient-holding (biologically helpful) stuff fills inbetween. "structural soil" is a "flip side" strategy: given a bunch of rock (which "drains" nicely), add growing media.