Soil Amendments – Don’t Amend Before Planting

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Robert Pavlis

Almost every book, and most web site tells you that you should amend your soil before planting a new plant. This seems to make a lot of sense. Few of us have perfect soil and we don’t want to put our new expensive plant into poor soil. If we amend it, the plant should grow better? That’s a common garden myth.

amending soil
Person Tree – don’t amend soil before planting

 Soil Amendments:

In this post I will talk about trees (including shrubs) since they can be affected more by this process than a perennial, but the principles apply to all types of plants.

In a previous post called Gravel at the Bottom of the Pot Helps Drainage I talked about the movement of water between two different types of soil. When different soils are next to each other, water tends to stay in one of them and not the other. Usually, water stays in the soil with the finer particles – say clay.

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?

Soil Science for Gardeners book by Robert Pavlis

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.

Girdling Roots

You have also created another problem that is even worse for your plants. You have created the perfect situation to encourage girdling roots.

Think about your plants roots. They start to grow and find themselves in some fairly good soil. Lots of air, nutrients and hopefully water. All goes well and the roots continue to get bigger. One day they reach the edge of the hole. Roots don’t have a brain and can’t think through the process, but plants are able to direct root growth to areas where they are finding the best growing environment. Roots start to grow into the native soil. Here they find less air if the soil is high in clay, or they find it very dry and nutrient deficient if the soil is sandy. Neither is good for roots. The plant then decides to put its energy into growing roots in the better soil. Since the hole is a round shape, the roots start growing round and round in the hole.

This is no different from the roots growing in a pot. You have all seen a potted plant with an overgrown root system. Roots go round and round.

For trees and shrubs this type of growth will result in roots choking the plant. The roots of trees and shrubs get thicker ass they get older and so they start choking each other. They can even choke the main trunk of a tree. Trees can die from this problem ro at the very least grow poorly.

Have a look at the damage that can be caused.

Don’t Amend Soil

The solution is both simple and inexpensive. Dig the hole, and replace the soil. Don’t amend it. Less work, less expense, and better for the environment.

Tree and shrub roots will have to travel great distances during their life time. Most of that will be done in your native soil. They might as well get used to it as soon as possible.

References:

1) Photo Source: Blackash and Pooketre.com

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

60 thoughts on “Soil Amendments – Don’t Amend Before Planting”

  1. I have extremely hard clay in niagara region also, want to plant lots (hundreds) of eastern white cedar trees, should I work in some compost, bark and manure with a rototiller? I have one for my tractor I could use

    Reply
  2. Wow, this is the first I’ve ever seen of this method, and I’m SO glad to find you & read this before I started my extensive shade garden. I have mostly clay soil. What is your opinion of root hume/fulvic acid concentrated soil treatment? I ordered 2 quarts of this, thinking I’d put it on the soil before I start planting, but the more I read about it, I’m finding that it’s supposed to be but around the plants after planting. Is this correct? Also, should I put a root boost in the hole as I’m planting, wait a couple of weeks, then water in the root Hume? Sorry ~ I’m learning, and any help would be appreciated!

    Reply
  3. Great post.I understand planting holes for perennials should not be amended. Please clarified for me regarding annuals and vegetable planting holes. Is there any benefit to adding compost, cold manure etc. to the plant hole? Thanks

    Reply
    • You should not amend the hole for the same reason. However, in the case of annuals and vegetables you want fast growth, so it is a balance between causing a potential problem and giving the plant some better soil to grow quickly. In bad soil you may be better off amending the hole.

      Better still is amend a larger area.

      Reply
  4. Hi,

    I have another question in regard to planting a honeycrisp apple tree. The descriptions state that it likes well draining sandy soil, it can handle some clay, but not much. I don’t want to amend per reading the above previously, but I am afraid that the tree won’t do well. What is your recommendation?

    Reply
  5. Hi Robert,
    I have recently gotten into planting shrubs. Fortunately all of the shrubs that I purchased like clay soil, which is what we have. It turns into a gooey mess that sticks together when wet and is almost as hard as a rock when dry. I watched some videos on you tube in regard to planting, which stated amending soil with compost when backfilling. I’m glad I read this before planting my new shrubs. However I did buy compost and with COVID won’t be able to return it. Can I mix it on top of the first couple of inches of the soil and then put the mulch on for the shrubs I planted last month? I don’t want to waste it (or the money). I had before seeing the videos on you tube uses about two scoops of potting soil mixed with the native soil when backfilling and put a quarter of an inch of potting soil on the bottom of the hole. The panicle hydrangeas I did this with last year are doing well. Thankfully I don’t believe I added enough to hurt the growth. I will be planting spirea, ninebark and another panicle hydrangeas. I was thinking of using the grass/sod (grass side down) that I dig to assist with creating a berm and also put some of the compost I bought. Do you think this is a good idea. I will also be putting down mulch.

    Reply
  6. Im planning on creating brand new flower beds. My soil is chunky clay. If I amended the entire bed and let them sit without plants for a few weeks, would that be ok?

    Reply
  7. A month or so ago I planted several bare root paper and river birch trees and seedlings in zone 6 and did not amend the soil for any of them. We have a lot of clay soil/. A couple of them are beginning to grow leaves (which is fantastic!) and a couple began to grow leaves and then the leaves died back. Any thoughts on what might be causing this?

    Reply
    • A plant tries to recover by growing both leaves and roots at the same time. If root growth can’t keep up, it gives up on the leaves.

      Reply
  8. After killing all my old fescue in my parkway with Roundup and living with weed blocker, gravels, and decomposed granite in this area for years, we’ve decided to scrape and replant succulents, ground cover, and some lower flowers… about 2 miles from the beach, major clay soil…so no amendment?

    Reply
  9. I unfortunately just discovered this article and discussion after planting a couple of trees where I mixed native soil with potting soil. Is there anything I can do to fix this? Should I dig them out and move them? I planted a Meyer Lemon and Turkey Fig tree this way. I’m so glad I discovered this before I planted the three trees I just bought! I live in Georgia where there’s dense clay soil so I assumed I was helping to loosen things up…….

    Reply

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