“Does this tree like clay soil?”
A question we sometimes loathe. A more appropriate question is, “How well does this tolerate clay soil?” We have a lot of clay soil here in Iowa, and sometimes that clay is covered by a nice foot or more of lush topsoil. Ah, what privilege! For others, (those of you in newer construction areas), all but a few inches of topsoil have been graded away through construction processes, meaning mucky, heavy clay is lurking one shovel scoop away. There are ways to work around clay.
With vegetable gardens or flower beds, you can improve soil structure and texture by adding organic materials like compost, mulch, leaves…etc. Just keep adding these year-to-year, and in time, you will see an improvement.
“Should I add some gravel, or sand when planting a tree to improve drainage?” NO. A tree’s roots spread very far and wide, so it is nearly impossible to amend the entire area where it will grow. Adding lighter materials, such as, peat moss, sand, or fancy ‘tree planting soil’ (sold at other retailers) to the planting hole, is not recommended either. The University of Minnesota has done extensive research on the topic, and have concluded that adding gravel to the soil will only make the problem worse because it creates a perched water table. Imagine digging a hole with hard clay and adding gravel at the bottom. It will pull more water out from the nearby soil, which will collect into the hole making it even wetter than before. Plus, over time, the clay particles will filter into the gaps in the rock allowing even more moisture to sit.
When considering light soil additives, your tree roots might be happy for a while in the light soil, but will not want to spread and break into the clay. Your best option is to dig a wide hole, score the sides of the hole with a shovel and backfill with the existing soil, taking care to break up/loosen the soil as you fill in the hole.
More tips for planting in clay:
- Clay soil does not drain well and is often water-logged, so avoid overwatering. Before watering, dig down a few inches into the soil to gauge moisture levels.
- Plant on the high side- It’s never good to plant trees and shrubs too deep, especially in clay soils. Raise the rootballs 1-3 inches above grade when planting in heavy soils. This is particularly true of evergreens, which don’t like soggy soils. If an evergreen has to go in a clay area be sure to plant them on the high side.
- Clay soils are often alkaline (high pH). PH levels determine the availability of nutrients that a plant can absorb. Certain species can develop nutrient deficiencies, like iron chlorosis, which is often seen on Pin Oaks and River Birch, but can be present in many other species. Here is a link to learn more about chlorosis. There are many reasons why leaves turn yellow, so we suggest that if you suspect you have a problem, to have your soil tested first before treating your tree. Iowa State University performs soil tests.
Bentley Ridge Trees & Shrubs with good tolerance for clay soil
Bentley Ridge Perennials with good tolerance for clay soil
Bentley Ridge Trees & shrubs with medium tolerance for clay soil
Horticulturist, Bentley Ridge Tree Farm