I don't see any issues with what you've done in the past. You can use whatever native soil that is granular enough (not big balls of clay) and mix it in with the amendments.

I've indeed noticed that the size of the hole you dig combined with what you backfill with greatly affects the growth rate of the plant. Once the roots hit a clay or rock wall or balls of clay, they don't go much further. ANd a small root ball = small plant. Hydrangea roots seldom go below 12" so digging a hole to max depth of 18" would help with soil drainage.

Current methods say "Do not amend for a hole" but if you do a large planting area then amending the soil is a good idea. I have Georgia red clay and I do not amend the planting holes (been at this house ten years) but at our last home the recommendation was to dig a hole many times the width and twice the depth - that was a lot of work and the results were no better than today's standards.

Here is one example of study done for example:

Hole size and amendment study in AZ

Thank you both. Usually the tags say, âÂÂdig a hole 3 times the size of the root ballâÂÂ, but normally IâÂÂm too lazy to do that. But I donâÂÂt normally plant shrubs in the first place, that can be expected (hoped) to increase greatly in size, only perennials. Since these hydrangeas were expensive, and I really do want them to be big, I thought I had better dig the big hole. But as you say, that is a lot of work: I would probably have to do it over the space of several days.

I read through that study you linked, hcmcdole. But it is about trees, and in a dry rocky climate. Do you think it still holds true in the Midwest with clay soil, and for hydrangeas?

The planting area is not large: basically I will be digging a hole for each plant at the edge of the lawn. When I amended the soil in my large raised bed about 8 years ago, I added loads of organics. Everything glows lushly in there. But the soil level seems to sink every year. I end up adding topsoil and compost on top, in and around existing perennials, every year. So (as the article states) the organic amendments do not last long, but decompose and the soil sinks. I thought maybe it was my choice of amendments (compost + peat moss, plus I think I added sand as well) that caused that, but maybe it would be true for any organic additions.

I am still not sure what to do. If I do amend, what would you recommend?

I know the study I linked to was about trees and in AZ but the studies are indicative of general plant health (in my opinion). I'm sure you could Google it even further for shrubs and hydrangeas in particular. If you are planting several shrubs in the same area you might till the entire area up and add your amendments at that time.

I've planted over 50 hydrangeas in the past 3 years and lost two tiny starter plants (should've babied them for a year or more), plus a couple dozen azaleas, hostas, weigelas, abelias, camellias, crepe myrtles, yews, Japanese maples, cherry trees, and so many more using native soil and a hole slightly wider than the plant. Eventually the "wall" will be met by the roots... Make sure your roots are not circling the pot though - that would be worse than a lot of other things when planting.

I see no issue with a little amendment but the only thing I have used in the past is Nature's Helper (a bark mixture to help break up the clay) but nowadays I don't even use that.

Here is a Limelight I planted 3 years ago (this is last summer's photo). It was a 2 gallon size when I got it in 2011. Nothing special except watering during droughts and the first year to make sure the roots would keep growing.

Before you plant please see my response to your post in the other forum (Shrubs?). It is very important NOT to amend individual planting holes but most especially in clay soil.

Thanks to you all. I planted them today, with wide holes, and using just the soil that came out of the hole. The soil for both was much better than I had expected. I have parts of the yard where it is really dense and hard, but neither of these were. With the second one I never even reached the clay layer.