Planting in Clay Soil

by Doug
(in my garden)

Planting in clay soils is one of those oft-debated horticultural practices.

Essentially, research showed that trees and shrubs planted in heavy clay had two responses:

Response #1

If the soil was amended and made very rich within a planting hole - the woody plant would establish and grow very quickly but when the roots hit the clay soils on the edge of the planting hole, they would tend to turn back towards the good soil. Plants stalled out and became ‘root bound” within the planting hole. It would take a few years before the roots would venture out into the native clay. The plant during this stalling out phase was more vulnerable to flooding with heavy rain or drought conditions.

Response #2

If the soil was simply turned over - a shovel of compost or bone meal put into the hole, the woody plant was slower to establish itself but once it started growing, it grew consistently and wasn’t as stress prone as the more pampered plants.

The lesson learned within the hort trade then has been to not amend heavy clay soils when planting appropriate plants.

And that’s the other lesson - only use appropriate plants. Trying to force fit a plant into a soil for which it is not genetically adapted is a waste of money and good garden plants.

Your choice as gardeners then with perennials is to find plants that deal with clay or totally amend the garden so you can grow the plants you want. This means that growing something like lavender in a heavy clay soil is going to be tricky unless you modify the entire area that influences this plant’s growth. Or you can stick to plants that grow well in clay and not worry overly much about doing the heavy lifting of modification.

The decision points come into play on clay soils that are not totally “heavy” but have some measure of sand/silt. These are the soils that can be modified with organic matter to produce larger perennial gardens. Trees on these soils still have to be those that survive clay because of the permanent nature of these larger woody plants.

Comments for
Planting in Clay Soil

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Amendments, Patience, and Gratitude
by: Mark

I live in the central valley of California. The soils are clay soils. We have very wet winters and very hot, dry summers. I started my first flower borders last year AFTER a landscaper put in over a thousand dollars worth of roses, lavender, and coral bells by digging a hole in the soil, filling it with good soil, and then putting in the plants - just the way Doug says not to do it. The result: the roses made it with a LOT of TLC but the lavender and coral bells all died. :-(

After reading a lot on the subject, I am now working my across the borders amending the soil with chicken manure, compost, and some granular gypsum.

The soil here has a very high sodium content, so gypsum actually works in this area, but it sure isn't an instant fix. In fact, nothing seems to be an instant fix. The bags and bags of compost seem to just disappear into the soil with seemingly little difference to the soil structure. Despite my love of instant gratification, I am in this for the long haul and will adjust my expectations by working hard continuing to amend the soil, being patient, and not planting any perennials other than roses and those plants that can thrive in clay soils until I have the soil composition to support them.

I wish I had found this site BEFORE I lost so many plants...but I'm really glad I did find it and I am very grateful to Dave and the community of commenters! Thanks!

clay-adapted plants?
by: mm in st.louis

How in the world do you know if the plants you want to buy are "clay-adapted"? My nursery people (just hirelings, bless them) certainly don't know!

Planting with drainage pipe
by: sharon

I want to plant new arborvitae in my water drench clay soil. I was told to dig a center trench about a spade width in the soil about a foot below the bottom line of the root ball hole. In the trench, put in a perforated flexible drainage 6"x10' pipe and bring the open ends of the pipe a few inches above the leveled ground beyond the perimeter of the arborvitae's mature tree drip line. Fill the inside of the drainage pipe with 1" to 2" river rocks then surround the pipe in the trench with a few inches of medium size gravel. Then plant the evergreen on top of it. This is supposed to help aerate the roots and allow drainage water to evaporate. My only problem is... which way are the holes in the flexible drainage pipe suppose to face...on the top or on the bottom? There is only one straight line of holes.

My experiene with clay soil
by: Sarosh Sepai

Thanks Doug for your inputs on clay soil. i have a large garden with plants all over the place?After a few years of perennial growth i am now seeing roots turning outwards, causing the shrubs and a couple of trees to destabilize and die out. I will seek clay loving plants from now on.

Question: Would you advise that I dig out these shrubs/plants make a bigger hole with compost, etc and replant them. One example is "rose of sharon" - I have lost two 5 feet tall shrubs in a year?

Planting depth
by: June

Remember, especially if you have clay soil, a little to high in the hole is much better than a little to low.

Roses in Clay
by: June

Just a (not so) brief comment; when I plant roses in clay soil I use a 3ft x 3ft hole, and replace at least 66% of the native clay with good garden soil. Living near Chicago I plant grafted roses 4in deep and I am especially careful to provide good drainage in the top 6in of soil. I use a good rose fertilizer early in the spring and lots of compost for mulch. I also mulch with compost (as in lots of) in the late fall. I think it gives the rose something to use for growing roots during the winter and an extra early start. My biggest worry is a really hard freeze in the spring. I remove the mulch very carefully in the spring, don't use water as it will water log the planting hole. For other plants, if you have to plant a plant the insists on good drainage, the planting hole must be as deep and wide as the mature plant would be tall and wide. In other words, no trees that don't like water. And why would you anyway, there are so many that like these conditions just fine?

Don't be discuraged!
by: CK from Ca.

I'm originally form Illinois and when we were kids my mom didn't have time to amend the clay soil.
There is an abundance of trees, bushes, perennials and annuals that will grow just fine in turned over clay. Look around at what your neighbors are growing, and most things sold at your local nursery or hardware store will grow in your local conditions.
If your really concerned, make small investments in your plants and see how they do.
My mother now 70 years old has a beautiful garden with a large variety of plants! I think she loves her roses the best!

Lavender as the Barometer for Clay Soil!
by: Margi

Well, Doug, this generally tells me more about what kind of clay soil I have than all the other stuff you've written (which I haven't done yet because I'm still waiting for Spring to arrive here in the Chicago area!!). I can grow lavender fairly well in numerous locations in my yard... Will you be posting a list clay-soil tolerant plants? Thanks, as always.

Doug adds that those are already posted. :-)

clay
by: Helen Millhouse

I am thinking the reason for a lot of plants not to survive in clay is that it holds the water making some plants drown in the mositure. We are in Pa and have plenty of clay but I have worked with sand and compost and just plain dirt. Not all the plants I plant survive but I keep trying. And maybe that is not the clays fault. Now I am going to look for ones that don't like a lot of water.

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Doug Green