Just because your soil is clay based does not necessarily mean it is poorly draining. If you have never done a home soil perc test, you might want to give it a try and see how it rates. If slower than desired, try planting high (root flare or top of container level 2-3" above grade) in a very wide but shallow planting hole.

GG, why did you mention container level 2-3" above grade? What if the flare is 3" below the container level?

Notice I said root flare OR top of container :-) Root flare should always be visible but no issues at all with it being above grade.

I read that wrong then - I took it as locate the rootflare or just use the top of the cotainer. Was thinking its simply locate rootflare and there is no or. What do you think?

I seldom find any issues with containerized nursery stock being planted too deeply. Typically, the root flare is always visible or just barely below the soil surface. I have found that it is B&B stock that often smothers the root flare under layers of soil.

Just to be clear, the root flare is still at soil level, you just raise the soil level in the area a few inches. You don't plant the root flare a couple inches above the soil right?

No. The rootball itself is positioned so that its top, including the exposed root flare, is above the existing soil grade by 2-3 inches. Then the excavated soil is mounded up to the level of the top of the rootball. OK to use amended soil if you need to to accomplish this mound and provide a gentle slope.

Thanks, that's (sort of) what I was trying to say. That makes it clear to me.

I’d be inclined to take the advice you’re getting, but I’d also satisfy my own gardening curiosity and experiment with soil amendment. I wouldn’t go crazy with it, but there’s no harm in setting up your own experiment. In a worst case scenario you lose the plant, but you may also be pleased with the results. If it fails to thrive you can move it. You don’t have to be a scientist to experiment.

I decided to amend a site for the planting of VIburnum carlesii. It wasn’t for drainage issues, but to improve fertility and moisture retention. So far, so good. I had the roof replaced a few weeks ago and their tarp thrown over the shrubs had an odd effect on both deciduous and evergreen plants where they came in contact. I think this is a temporary issue, and hopefully next season it will resume its healthy ways.

I routinely have to excavate both potted and b&b stock to expose the flare. Sometimes by as much as 5". It's appalling, frankly. These plants come from the creme de la creme of PNW nurseries (Iseli and Buccholz primarily). I teach workshops for Master Gardeners and for the ACS on planting conifers and I use my own containerized stock (waiting for planting) to demo. People are shocked at how much excavation is necessary. My soil is adobe clay so I plant most conifers on top of the existing grade in mounds of amended soil, composed of roughly 60% loam and 40% 1/4" lava pebbles (no fines). Eventually the roots find their way into the adobe but by then they have a decent-sized root system.

steve , I like gypsum so far...it seams to break up sticky clay pretty well , and add course sand

as you say used over area rather than only in hole

ron

Where does your 60% loam come from, given you have adobe clay soil?

University level experiments including use of control (untreated) plants dating back to the late 1960's have repeatedly shown that woody plant response is better when planting hole backfill is not amended. This includes tests undertaken on more than one soil type and using varying kinds and combinations of amendments.

That plants in random plantings have not died every time amending of individual planting holes was done does not establish that this is a successful or superior method.

The main issue with amending of planting hole backfill is how the difference in textures between the amended hole and the surrounded unmodified soil affects movement into and out of the hole. On a damp clay soil this effect can be enough for recently planted specimens to drown during wet conditions, due to the amended hole functioning in the manner of a sump.

Amending of an entire bed, where the interface between the amended area and the soil beyond is some distance from specimens planted therein is different because only the amended soil near the edge is being affected. However since organic amendments decompose and vanish over time - often after only a year in a hot climate - the value of using them on long term subjects (really anything that will be in place for more than a year) remains questionable.

I get it locally from a landscape supply place. I get the material with the least amount of organic material. The lava pebbles provide stability and drainage. I decided this based on lengthy conversations with my arborists.

"That plants in random plantings have not died every time amending of individual planting holes was done does not establish that this is a successful or superior method."

I don't recall anyone contributing to this thread stating it was a superior method. That's your interpretation. I'm merely advocating for gardeners to experiment. There's nothing wrong with this. Some people might take this as a personal affront, but I think it's just a healthy exercise in gardening. To each their own.

' Amending of an entire bed, where the interface between the amended area and the soil beyond is some distance from specimens planted therein is different because only the amended soil near the edge is being affected. However since organic amendments decompose and vanish over time - often after only a year in a hot climate - '

I personally like this idea. About amending a larger area on say a hard clay soil. Even though the amendments may not last more than a year, the initial improved drainage they supply, will give the new plant a chance at a better start. Once the amendments 'vanish' the plant should be somewhat more established and the roots more able to cope.

Yes Bill! My mounds have settled over time but the plants are well-established and have made their peace with the native soil.

Thanks for all the comments. I have another issue regarding planting on a steep hillside where I was amending the hole so that water will penetrate down into the root structure rather than just running down the hill. I try to create a little shelf for the plant to sit on and water to collect before it runs off. Can't amend a large area as then the hill would just wash away. Pretty sure I've created some bad situations where water is just pooling inside the pocket I've created and/or bad root penetration into the surrounding soil. This is the sticky clay with slate underneath. The only thing I've managed to kill here are some black-eyed susans and a sedum. The BES seemed to die from thirst (I didn't water very much) while I'm pretty sure the sedum drowned over the fall/winter. I have other sedums that survive and even some escapees that are rooting on the hill. Its probably harder to kill viburnums and forsythia and the Irises seem to love it.

My plan (for now) is to just use gypsum in the hole and only amend the top inch or two of soil with ~20% pine bark fines and cover with cypress mulch. Do you think Pinus strobus (weeping) or densiflora (variegated) would do well here considering the hill provides much drainage? The sun exposure seems good to me as the hill faces south east and may get a little overhead shade and very late afternoon shade in the summer and potentially even more winter shade except during the middle of the day. Plus it has good protection from the wind.

I didn't notice this in the previous posts and you may already do this but anytime I mound my loose, sandy soil or if slightly on an incline, I must use a layer of wood mulch, at least 2" deep. Otherwise, the first time it rains, everything washes away or levels out, depending on. The mulch helps hold the soil but I suppose if enough water runs down the hill, it won't help. That may take other measures to channel water away from the hillside, like some form of mesh/straw covering across the area.

GG,

your soi perc test link gives an error.

Yes I always mulch right away after I plant on the hill. Trying to keep the soil there there. It's pretty much all mulched now. Except where it's too steep. I actually put a "U" stake in the ground cover to hold it in place.