On the flip side, when it comes to planting trees and shrubs, your best bet is to plant the right species for the soil that you have, instead of trying to change the soil. The vast majority of Bentley Ridge’s plants can take a fair amount of clay, but some are better than others. See the list of recommended plants that have the best tolerance at the end of the blog.
“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:
Horticulturist, Bentley Ridge Tree Farm