How to plant a tree in heavy clay soil

I get a very high survival rate with the CSFS bare root seedlings, but it takes some attention.  These are the steps I use for planting perennials in heavy clay soil.

  • Dig a square saucer shaped hole, that has long sloping sides and corners. Round holes, especially in heavy clay can encourage root bind. If you stick in a shovel and the sides look ‘glazed’ or smooth you are at risk of creating a solid clay pot that the plant will have difficulty escaping.  The saucer shape forces the roots toward the surface for more oxygen and nutrients while the square or jagged corners can help the roots stop circling and push out of the hole. (A fence post auger is the absolute worst for heavy clay. I have seen entire auger-planted orchards die 8 years later from root bind.  If you use a post auger, go back after and re-dig the hole by hand.)
  • Possibly even worse than a round hole is a hole that is filled with compost and fertilizers. Plant’s roots tend to avoid texture and nutrient ‘differentials’ and will stay where things are easy.  A heavily amended hole with compost or other fertilizers,  can create a ‘lazy’ tree that doesn’t try and get out of the hole. It will eventually root bind. You can use a very small amount of compost to inoculate the soil with bacteria and a multi-strain mycorrhizal inoculate can also help. Dipping the roots in a light kelp solution helps them recover from transplant shock and re-grow root hairs.
  • When you dig the holes, before you plant, fill them with water to check the drainage, if the drainage is very slow, pay close attention to how you water through the season as it will be very easy to over-water and drown them. They will need regular water every 3-5 days, but not over watering. I usually give them 1-2 gallons of water every 3 days.
  • Make sure the back-fill soil is very fine, no clods, rocks, twigs etc. When you plant, focus on getting the roots back into the three dimensional shape they were in when they were uprooted. I screen the soil to a very fine texture and if it is pure clay, I sometimes add a small bit of sand or coconut coir. Don’t bend the roots to fit the hole, it is better to make the hole bigger or prune the roots.
  • Check the root to top ratio. If the roots look severely pruned then you will need to prune the top to match the roots. You can even over-prune the tops slightly to give the roots more weight.
  • Don’t expose the bare roots to sun for more than 30 seconds. The microscopic root hairs are probably already damaged and sun will quickly kill whatever of them remain.
  • Make sure your planting depth is correct, not too deep or above ‘grade’.
  • After planting, feel free to amend at the soil surface with compost and mulch. Perennials are mostly adapted to top-down feeding, so creating fertility at the soil surface will encourage natural development.

2 thoughts on “How to plant a tree in heavy clay soil”

  1. Thanks, Aaron. This article was very interesting and “made sense” to me. I live in Northern Utah in Cache County where the soil is very clay. I’m ‘putting in a yard’ but am not an experienced gardener so have been researching ideas for planting trees in clay soil. Of course, my trees are not bare roots but generally come in a pot or a burlap bag. I’ve also been going for larger trees which complicates things. I just tried this method with several ornamental pear trees and I really liked how it “felt.” Like I said above, it just made sense to me.

    I do have a question: I’ve got a 10 foot Alaskan Red Cedar I planted recently in the same heavy clay soil. By and large, it looks like it’s doing okay but there is a bit of yellowing here and there. It doesn’t appear to be getting worse but it’s kind of hard to tell with the heavy foliage on a weeping cultivar. The guy who planted it didn’t do any real amendments to the soil. He just dug a hole, removed the top of the burlap, and covered up the root ball. The soil does tend to drain pretty well but can you give me any advice other than just “lots of water and leave it alone”? Thanks!

    • Hi John,
      Thanks. Glad it is helpful.

      I have a red cedar I’m trying out as well and it is also showing some yellowing at the ends of the branches. Possibly the soil is too alkaline, some nutrients are locked up or particular symbiotic bacteria or fungi aren’t present in the soil. I would add a lot of compost and worm castings at the surface, 2-6 inches deep, and out in a circle with a diameter as wide as the tree is tall and then mulch over the top of that with wood chips. You would also try lowering the pH slightly with citric acid. It sounds like your soil is draining well enough, but overwatering in heavy clay can also cause waterlogging and deprive trees of oxygen.


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