I live in Houston and I throw old container soil to fill holes my doggies dig in the yard

When I plant an acid loving plant I mix azalea or rose bag dirt and pear moss and throw that in a large planting hole. I have used fine bark mulch as my acid fill in soil and no Plant has died yet.

I’d use coffee and dried leaves in hole or as top dressing.

The popular horticultural convention is NOT to amend individual planting holes, regardless of the type of soil you are working with. There are numerous reasons for this with the primary concerns being soil interface/water penetration and the delay in proper establishment of new plants. What is dug out of the planting holes is what gets put back in.....unamended.

There are a couple of additional ways to address this. You can amend an entire planting area, as spreading any amendments over the widest possible area will reduce or eliminate any soil interface issues. Essentially you want the soil texture to be as totally uniform as possible over the widest area. But this requires the area to be completely bare/unplanted or anything in it dug and stored until the amending process has been completed.

Or you can use whatever amendments you prefer as a mulch or top dressing. Just not worked into the soil.

And you really want to avoid individual planting hole amendments when dealing with clay. The amended soil will hold water and the clay will prevent fast drainage so you wind up with a bucket or bathtub effect and rotted roots. With clay, dig a very wide and shallow planting hole and plant high, with a portion of the root ball above grade. Break up and mound up the dug out soil to just the top of the rootball and apply whatever amendments you ike as a mulch.

Putting the uncomposted wood chips in the soil and then trying to compensate by adding ferts doesn't work well. I know. I tried.

The thing about never amending the soil at all, before planting a tree, I take with a small grain of salt. How can you draw a conclusion like that for my previously uncultivated rangeland based on an experiment done at a field in a meticulously cultivated ag station somewhere?

That said, there's no reason to go to town with a new planting. A bag of spent mushroom growing medium in a very wide hole isn't going to hurt anything.

The comments on clay holding water are spot on. It will drown roots or cause girdling if you make a clay pot out of the hole. The incredibly small particle size of clay and its negative charges allow for a large water holding capacity. That soil interface is important. Natural soil interfaces are horizontal horizons that plants understand. Even my huge oaks have roots that spread out, not down. The best success I have is with compost or other nutrient sources on top. If you really want to do something good, inoculate the roots.

Even though there are disagreements on certain points, there are merits to all the comments thus far.

The first point that I think will help is to delve into your question a little more...

When you speak of amending 'holes', you're talking about holes for trees and shrubs... right?

And when you say... "Since starting gardening I mainly use store-bought bagged garden soil, mixed with the native clay soil..." - do you mean perennials, or vegetables perhaps?

Keep in mind that 'holes' for trees and shrubs are 'one and done' for each hole. In such instances, if you have bought a tree, bush, or shrub - and plan to plant it pretty much immediately - the best understanding of current thinking on the matter is to do as described... just dig out a hole and plant (there is more to it than just this simple phrasing, but in the context of amending... evidence shows it isn't necessary, and in certain circumstances, it increases the odds of creating problems.)

However... if, for future gardening - or simply soil health - you want to improve the soil in a given space, then amending the soil with readily broken down materials can be extremely beneficial.

Let's say you're wanting to plant a future perennial bed. If you turn the soil, amend heavily with leaves, coffee grounds, compost, etc... and let that incorporate for a few months, you will be feeding the soil web for long-term soil health. You can then plant your perennials, then just keeping it mulched will vastly improve a clay soil.

Same with planting trees or shrubs at a future time. The idea is to allow time for the additions to incorporate into, and improve the soil structure of a given area.

I don't recommend this technique with 'largish' pine bark, or wood chips. These products require lots of nitrogen and oxygen to break down. If you bury them and don't/can't turn the soil, you'll be creating issues. It's not the end of the world type issues, but issues non-the-less. These are much better suited to the soil surface as mulch. There they will receive oxygen, and even nitrogen from rain. They will host beneficial soil microbes, 'macrobes' (insects and such,) and fungi. They will allow the soil to 'breath', and they will slowly decompose into the soil web.

Veggie gardens are a bit of an exception. They can, and should be amended with organic matter a lot more often than perennial beds. This will help a clay soil. And, unless you are going completely 'no-till', they will be turned at least once, and often multiple times throughout the growing season. There is no shortage of oxygenated soil, and they often receive sufficient additions of nutrient supplementation. I still don't recommend turning pine bark or wood chips under the soil, but they can be used as mulch if you wish. However, most people save those large wood products for mulch in the perennial beds. I use them as path material in the veggie garden. In any case, even in clay, the percentage recommendations for organic matter is below 10% of total mass. The deeper you till, the more you can add. Once your clay begins to see improvement, then you can safely add about 1/2" of compost in both the spring and fall... or about an inch - to maybe 2 inches - per year.

@rgreen, a great post and I agree with almost everything you wrote, especially as relates to this specific case. This is the internet though so one small disagreement: I think that if you're going to bury wood products, the larger and chunkier the better (rather like hugelkultur).

For buried wood, I believe it's the surface area that drives how much nitrogen (and likely oxygen) is 'tied up' especially in the short term. Think of the difference between burying, say, branches or chunkier bits of wood compared to sawdust: the sawdust will have millions of times the surface area for organisms to colonize. The fungi that gets inside larger bits of wood works differently (and some supposedly decompose with little nitrogen). All that said, wood chips are going to be closer to sawdust in this respect and this doesn't change the main thrust of your advice.

kokopellifivea, perhaps you misunderstood my posting :-) I never said "don't amend".......I only stated that if you wish or need to amend, do so over the largest possible area, not individual planting holes.

"How can you draw a conclusion like that for my previously uncultivated rangeland based on an experiment done at a field in a meticulously cultivated ag station somewhere?"

Because it really does not matter with the type of soil or even its fertility. It is the interface and textural issues one is dealing with and those will remain present regardless of soil type. Radical changes in soil texture between heavily amended planting holes and the surrounding indigenous soil will limit proper root development and establishment, And the water/soil interface issue can definitely affect establishment or even survivability as water percolation through heavily amended soil/planting holes will be adversely affected, often with disastrous results. The only time amending planting holes would really work to your benefit was if your "uncultivated rangeland" had the same textural and structural elements as whatever it is you are adding.

btw, amendments applied as top dressing or mulch will still have the same positive effect on soil fertility and stimulating the microherd population.

I had great success with hugelkultur amending. That means amending with large logs. In fact, I had much better survival rate with holes with logs than without. The secret is in having a large chunk (I put about 40 lbs per fruit tree), so that there is a favorable surface/volume ratio and N does not get sequestered. The roots will get into the wood and the wood decays over years. I now have chunks of wood buried all over my garden too, some as large as 50 lb. I no longer fertilize.

Numbers of planting hole amendment experiments have been conducted over a long period of time in more than one location, using varying combinations of amendments and soils. With a consistent outcome resulting.

A leader in this area (analysis and improvement of the growing of landscape plants) has been Carl E Whitcomb, who first noticed that trees in unamended planting holes were growing faster than those in amended holes in the same experimental plots during the 1960s.

Click on Establishment of Container Grown Plants in the right hand column for commentary from Whitcomb (about watering, amending and fertilization of new plantings):

https://rootmaker.com/knowledge-center

Thanks for all the help. I'm probably deluding myself, but wanted to try something in my small yard. When I wrote "Is it beneficial in the long run..." I really meant 2 years and beyond...not so concerned about robbing nitrogen the 1st year or so. (Also being 60-something in age, "long term" is relative, haha.)

Briefly, my new holes are mostly for perennials, and some annuals. 1 or 2 shrubs, but not trees. I'm moving 5 potted roses into the ground soon. Also berries, tomatoes, various jasmines & other fragrant plants and bulbs. I will be dividing a 2 yr old clumping bamboo, and moving two sections to a new area.

Most of them will be about 8 inches above ground level. In the back yard, there's less and less lawn each year, as I add various raised beds (4. 8 or 9 sq ft), lasagna-type beds, and regular ground level holes surrounded by mulch.

Last year I grew a couple dozen Daikon radishes (~ 12 in long) with the idea of breaking up the clay locally. I planned to do it again in coming years. I may try soybeans or other legumes too.

After reading/hearing horror stories about the soil interface barrier and bathtub effect, I tried to make it a more gradual transition. E.g. once I got the desired hole size, I further stick a garden fork around the hard periphery many times to break it into loose chunks, widening the hole a bit further. Also, drilling many holes with a 3/4" augur bit (photo below) to give the roots "a foot in the door". I realize all this may have unintended results, but wanted to try something. Thanks again for all the replies. (should have spelled it "auger")

Sorry that's not really going to do anything. If existing soil is apparently not suitable for any particular kinds of plants that you wish to grow excavate and replace over a sufficiently large area. Or put different soil on top, plant in that without combining the two soils.

Flowering annuals and annual vegetables are different than long-term plants, that produce large root systems and will be in place for many years. Also the former have often been developed from wild species that pop up in recently disturbed sites where high percentages of organic material may be present in or on the soil. Unlike many perennial plants, including woody kinds - which may often be adapted to soils with comparatively low organic content.

With small, ephemeral plants doing best in organically rich soils amending of special beds made for these specifically is feasible, even desirable. But even for these problems can result if soil organic content is made too high.

armoured... yeah, thank you for making the distinction between larger-mass wood, and chips. I think glib hit the nail when pointing out surface area.

I personally have the superpower to find every cable tv cable and phone line in the area when I dig. I hope to move up to water lines one day and after that I hope to drop my auger on the main power line that runs angularly through my lawn.

JOKING!

Seriously though dropping vertical firewood in a variety of places underground is something I have done for a while now. I do not burn it and cannot chip it, but in my clay it acts nicely in the 2ncd and third years.

Excavating and replacing the existing soil is unnecessary and putting a different soil on top could interfere with the soil interface and create more problems.

The solution to soils that do not drain well, or drain too well, is to add a lot of organic matter to that soil over a large area. In clay soils never just amend the planting hole since that simply creates someplace for water to accumulate and prevents that water from moving out in a timely manner.

Always call before you dig! Even in parts of your yard where you think there are no utilities, you may not know where they go. TV cable companies are notorious for zipping lines in very shallow and leaving the old ones. Mine goes all the way across my back yard.

I put some rotten firewood chunks under a new raised bed (very shallow but it was for vegetables after all) and they did very well even the first year. I'm convinced it works.

It always gives me heartburn when I read about the evils of clay soil. For every disadvantage, there is a merit to clay soil. The key is to learn how to work with it. There have been excellent points made here about foreign and native soil interaction, the infamous “bowl” effect and organic material used as amendment and/or top dressing. However, the fundamental question is: how well does my clay (or whatever type) soil drain? One MUST determine this b4 getting on a rampage about bowl effect, etc. I was lucky that mentors encouraged me to answer this most basic of questions. Armed with that info. I could make decisions for or against mixing soils in holes, plant selection, use of raised beds, etc. My azaleas do not love clay soil but I amended the wide and shallow planting holes and after nearly 10 years, they’re doing well.

/diy-soil-drainage/

Do the above (or a version or of it) before continuing with your planting and soil improvement decision making.

@Dan H. When digging holes, I do like you and disturb the walls by punching holes. But going by that picture, your soil looked very, very dry. You can put all the magic dust in your soil, planting hole or not, and your plants will not do well. They need to drink! Good luck. You seem genuinely thoughtful and interested in learning, that’s counts towards success.

Wide and shallow - that's my new mantra. Root ball partly above grade. Raised beds. I was focused on helping root growth penetrate the clay. I'll see what I can do to improve drainage. I'm at the mercy of the variable seasonal rainfall.

Thanks BossyV, I've read of your exploits elsewhere. That photo of the dry looking hole was from late March 2016. I've done better since then. We had decent rain a few weeks earlier, followed by some 90 deg days. The grass still looks dormant. I've read 'don't work with wet clay', but mine drains so slowly it's rare when it's not at least partly wet (well, most summers it will dry out severely...I've contemplated dropping organic material down the big cracks that develop in our area).

The auger drill bit only works when the clay is somewhat wet, it pulls out nice thick curlicues. It won't penetrate hardly at all when it's dry. My soil plight was probably worsened during house construction, by heavy equipment causing more compaction. There also seems to be some crushed builders stone plowed under, in layers here and there. The first hundred weeds I removed from my new lawn with a weed puller (screwdriver shape), I usually struck a stone an inch or 2 beneath the weed.

But life goes on. Thanks everyone for all the information, not what I wanted to hear but it's sinking in, live & learn.

Dan, do the drainage test. Divide your back yard in quarters and test each section. As you probably already know, there’s enough variation in a single yard for plantings to respond differently. Testing for drainage AWA for soil content (NPK and trace minerals) will arm you w/knowledge to work w/your soil successfully (not that Ma Nature isn’t going to throw you a curve ball every now & then and throw concepts, theories and wisdom out the window, ha)

ETA: is providing supplemental water not within your budget? If so, you might need to focus on xeric plants. BTW xeric plants do need water but unlike hybrids they look decent to good even during severe droughts.

Alright BV. I will certainly look into the resources provided here. Sure I'll water to keep keep the grass going, and a soaker hose around the foundation. But not enough to prevent cracks further downhill (the back 0.040) so common to this locality. In wet months, the drainage from my ready-to-use prepped holes is miserably slow. Gradually I'm sure I'll trend toward xeric and lower maintenance plants. Especially if the rose, blackberry & bougainvillea thorns get the best of me, and the mockingbirds get all the berries and tomatoes!

I have a back 40 section like yours that gets no supplemental water. Were I to plant something there, I’d have to use a pickax and would only be able to get big chunks of clay. Of course, I do not Plant there. One does need to pick one’s battles, ha

ETA: I also have the big cracks that you mention and have wanted to fill them up, mostly b/c I’m afraid of breaking my ankle on one of them, I just pray for rain to shut them back and do nothing else, sigh

I use tent stake augers, because I am cheap and they are wide.. I cut the hook end off and load them into the drill.

Daikon will give you large permanent deep channels. and in the south you can plant them late. no drilling equipment needed.