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.
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?
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:
Hi Robert what is the effect of putting compost in planting hole for vegetable (cabbage for example).. is it bad as well?
Amending a potting hole creates a watering issue. The soil in the hole tends to stay wetter or drier than the surrounding soil. It also limits root growth out from the hole. Just mulch with the compost.
I have a question on tree roots and hardiness and this seems the best spot to ask. Can a super hardy peach root make a tender peach (scion) a little hardier over the winter? I live in Zone 3, and I once budded a peach (not hardy here), on a Manchurian wild plum (super hardy). The peach hardened off earlier than the other peaches (dropped its leaves), and there was certainly some hardiness increase at that time. I am wondering if a super hardy root can increase the midwinter hardiness as well.
I don’t know – I will post the question on our Facebook Group: https://www.facebook.com/groups/GardenFundamentals/
I add worm castings every time I plant trees, and always have awesome results.
Since you do it every time you do not know if the worm castings are making a difference.
Thank you! You have saved me a lot of money and work!!!
What about adding mycorrhizae to the roots of my new tree (sugar maple)? Can I do that and not ammend the soil and get quicker growth?
You can do that – but it won’t help the tree grow. Most garden soil already contains mycorrhizae.
Hello, I just read your post, and this will be my first time planting an Maiden Grass ‘gracillimus’. In the planting directions it states to amend the soil plus top it off with fertilizer. Is this o.k for this type of plant?
No. Plant it in your native soil and don’t add fertilizer. Grasses do not need to be fertilized unless your soil tests shows a deficiency.
You might also be interested in this post. It talks about washing roots before planting trees, but everything in it also applies to perennials.
http://www.gardenfundamentals.com/washing-roots-planting-trees/
Thank you for confirming my suspicion that you should not supplement. The garden center tried to tell me otherwise today. What about fertilizing for acid lovers like dogwoods ? They also sold me a starter fertilizer and told me to use an acid fertilizer or sulfur here in sw Ohio.
Starter fertilizers are not needed, unless they are providing a nutrient your soil test shows you need. the idea that newly planted things need fertilizer is wrong.
Is a dogwood an acid lover? There are many types of dogwoods, and a number of them grow naturally here and our soil is pH 7.4. Cornus kousa likes neutral to acidic soil, but it also grows here at pH 7.4. Trying to change soil pH is difficult, and must be done continually – probably for ever. As the root zone gets larger you will need to add more and more acidifiers to cover the ground over the roots.
Your location tells me very little about your soil. My soil is alkaline clay, but I can drive 20 minutes to a friend that has sandy acidic soil. Find out what kind of soil you have. A garden center will not know this and therefore should not be recommending fertilizer.
I am going to start trying this method as well.
Thank you
But I garden in Florida! Our soil is terrible!
What does the tree root have to do once it gets outside of the amended hole? It needs to grow in your native soil. If it can’t survive there – it is the wrong tree to plant. You might as well find out sooner than later.
I whole-heartedly agree with this advice re soil amendment, and I would add one additional comment. There is even evidence to support the concept of washing the potting/nursery mix away from the roots of your tree before you plant it as well (see the Gardening Professors https://sharepoint.cahnrs.wsu.edu/blogs/urbanhort/default.aspx). Nutrient-enriched potting soil between the roots may induce the same problem, girdling roots and premature plant death. This applies to nursery trees supplied in “root balls” covered in hessian. Despite the warnings of dire consequences by the staff of my local big box nursery, I removed the hessian, washed the tree roots thoroughly and planted my trees (maples) in un-amended garden soil with ample follow-up watering as recommended by the good profs to help the trees establish. So far, no losses and readily observable (albeit modest) new growth of all trees (6) within the first year. I now wash the soil off the roots of everything I plant (trees, perennials, etc) before I plant them, and never amend the soil before planting. So far, no regrets.
Interesting point about washing off the soil. I am not yet convinced this is the best practice and plan to do more research on the topic.
I have two concerns. firstly, I tried it with a couple of trees and they both really suffered – one almost died. Their problem could certainly be due to other reasons, but I plant quite a few trees and don’t normally have a problem. Secondly, washing the soil off must do a lot of damage to the fine root hairs and fine roots. I am not sure how fast these grow back.
It does require more research and I will write about it in a future post.
So what’s the update on this?
I have been trying to wash soil off root balls before planting for a couple of years, and the trees have been doing quite well. I think the key is to keep them well watered. With fewer roots, watering is more important.
I have also been using thicker layers of wood chip mulch – about 8 inches as per Dr Linda Chalker-Scott’s recommendation and this is working well also.
I am not clear on this, how much do you replace? do you mix some native soil with it? I usually do not amend but I do add good soil into the hole and mix it in with some native soil to sort of train the roots to acclimate to its surrounding IDK
I either don’t understand your question or you missed the point of the post. If you are “adding good soil ” to the hole you are amending the soil. Don’t do that. Just replace the original soil.
Are you washing them down to bare root? I always thought that the root ball was the heart of the tree.
I now wash most of the soil off all trees and shrubs before planting. The soil in the pot is so different from my own that this makes sense. More importantly it allows me to see any root problems before I plant.
I know it goes against everything we learned or think we know about tree roots.
I think it comes down to this. Is it better to cause some growing issues in the short term or plant the tree incorrectly and have long term problems. Roots grow new roots quickly.
I just don’t quite understand what you mean with replacing the original soil? Isn’t that will create two different types of soil? What the difference with amending soil in the hole?
The soil you dig out of the hole goes back into the hole, with no amendments.