Heavy clay tree planting

Asked September 3, 2018, 8:34 PM EDT

I purchased a Russian Hawthorn (#15 container, 1 1/4" dia.) on Sunday afternoon for a particular spot. Upon digging the saucer-shaped hole for it, I discovered the heaviest clay in my yard to date. I understand that a Russian Hawthorn is tolerant of clay but I decided to stop and ask what to do. Is it ok to still plant given the heavy clay? If so, should I amend the backfill with something? I'm following The Science of Planting Trees (GardenNotes #633) and live in Castle Rock at 6,500 feet. I might be able to find another spot in the yard but the soil on my lot is horrible.

Douglas County Colorado

1 Response

Page 7 of garden notes 633 discusses both wet soils and clay soils. Where you have clay soils you will indeed have compact soil and wet soil. I would not hesitate to amend the soil so that this clay can be broken down but definitely extend the planting area out for the roots to spread into amended soil. See the garden notes for illustrations

Modification for Wet Soils
On wet soils, raise planting depth so that one-third of the root ball is above grade. Cover root ball "knees" with soil, gradually tapering down to grade. Do not use mulch to cover knees, as roots will readily grow in moist mulch but will be killed when the mulch dries out. [Figure 12] Figure 12. On wet soils, place root ball 1/3 above grade, covering knees with soil tapering down to grade. Modification for Compacted Soils On extremely compacted soils, rototilling a ring around the backfill area to a width of four, five, or more times the root ball diameter may be helpful. This should be done after planting is completed so the soil is not compacted by foot traffic during the planting process. [Figure 13] Generally, at least two structural roots should be found in the top 1-3 inches of soil, 3-4 inches out from the trunk. On species prone to trunk circling roots (such as crabapples, green ash, hackberry, littleleaf linden, poplar, and red maple), the top structural root should be within the top one inch of the root ball. Top of root ball rises 1-2 inches above grade. No backfill soil covers top of root ball. Backfill soil covers root ball "knees" and tapers down to original soil Tree sits on undisturbed soil. Saucer-shaped planting hole, three times root ball diameter. 633-8 Figure 13. Rototilling a ring around the planting hole may help roots spread into compacted soil.

Amending soil is covered on pg 14.
In summary plant the tree where you want it using the guidelines in Garden notes to address your heavy clay soil. If you plant anything in that spot it will need amending our good old clay Colorado Soil.