What is the difference between replacing soil and amending soil?

Question

I came across this article and I find that it goes against everything that's said about soil amendment before planting. I've copied bits of it down below.

You are planting a new tree, and you want to do everything that you can to make it grow well. You dig a hole and examine your soil. It might be very sandy, or it might contain a lot of clay. You decide to add organic matter to ‘condition the soil’. You complete the planting process, and water well. What happens?

You have created a big hole in the ground. Around the outside of the hole you have your normal native soil. Inside the hole you now have a different kind of soil – it contains more organic matter and is your amended soil. You have created the same condition we talked about in the previous post, namely two types of soil in contact with each other. We know that water has difficulty moving between two types of soils. You have created one of two problems depending on the type of native soil you have:

1) you have created a hole that retains water. Excess water sits in the hole and does not move away, drowning the tree roots.

2) you water the area but water tends to stay in the native soil and does not enter the hole. Your tree roots are dry.

Neither is good for your tree. So just replace the soil. Don't amend it.

Answer 1

It probably does mean putting back into the hole the soil you just dug out,rather than replacing all the soil with other soil. But the most telling phrase is 'you dig a hole...'. If you're going to plant a tree into soil which is solid clay or generally poor,then proper preparation of the whole area is called for. That means you dig over a much wider area than the single hole you require to plant your tree and incorporate organic material across the whole area, leave it to settle for a week or so, then dig a hole and plant the tree straight into it, without adding anything else, other than possibly a mulch over the top.

I'm currently in the midst of preparing an area of soil 6 feet wide by 22 feet long, but all I want to plant in it initially is 2 (eventually) large shrubs and a single,small tree. The soil is heavy clay and full of rocks, hence the preparation of digging and amendment with organic material (in this case,composted manure). This has meant extracting 3 or 4 smaller plants I want to keep while I do the preparation, which will eventually be replanted in the same area. I could just have dug 3 separate holes, but whether you add organic material to the hole, or simply replace the soil you've removed when planting, you still end up with a 'sink' where rainwater will immediately collect, because the surrounding soil is undisturbed and heavy clay, and water will take the route of least resistance. Which then means your plants are sitting in a wet hole, as described in the extract you included in your question.

The lesson is, yes amend the soil,especially if its poor, but do it over a much larger area than just the single hole you need for a particular plant. If that is not possible because of the presence of large shrubs in the area, then digging a hole and planting straight into it and replacing the original soil (known as backfilling in the UK) is better, followed by a 2 to 3 inch layer of organic material as a mulch, preferably over the whole area if the soil is particularly heavy or light.

Answer 2

I was confused by the "replace the soil" phrase at first, but then realized that the author meant "...just put the soil that came from the hole back into the hole. Don't amend it." This is the exact same advice I learned in my degree program and which I and my coworkers have given plant purchasers for years. Where I live, clay soils are very common - if someone plants a shrub or tree and puts "good black dirt" (as it's known here) into the hole instead of the clay that came from it, they're very likely to create an underground flowerpot and drown the plant. And then they complain that we sold them a "lousy" plant and want their money back!

I have known some people who've amended the soil for their plants, but they've done so over a large area and only concentrated on surface amendments and organic mulch.