Article: Digging into Clay Soil


Clay Soils

What to consider when planting trees in slow draining clay soils. Poor drainage often leads to higher soil pH's. If you have compaction and poor drainage, salts and other materials may accumulate, rather than leach out through your soil over time. Also, when you have less drainage, you have less bacterial activity and less root growth. When all this happens, soil pH gradually increases and fruit trees languish. There are few fruit trees which do fine in clay soil such as pears, persimmons, and sometimes plums. In contrast, sweet cherries and apricots will often struggle in heavy soil.

Clay is often full of nutrients, but these elements are bound up due to the percentage of Magnesium in the clay. The high Magnesium will tie up critical nutrients for your trees and plants. Typically it will prevent the uptake of potassium and phosphorous. Two critical components. The good news is gypsum or lime (depending on soil pH) will alleviate the problem. Lime and/or Gypsum are primarily composed of calcium. Calcium is one the most critical element for soil structure, it's critical in building sturdy trees with thick cell walls, hence, increasing resistance to disease.  It’s relatively cheap and useful. A few cupfuls broadcast around the trees every spring will make a big difference in your trees vitality.

Digging a bit deeper. Elements having an electrical charge are called ions. Positively-charged ions are cations; negatively-charged ones are anions. The most common soil cations calcium, magnesium, potassium, ammonium, hydrogen, and sodium. Cations held on the clay and organic matter particles in soils can be replaced by other cations; thus, they are exchangeable. For instance, potassium can be replaced by cations such as calcium or hydrogen, and vice versa. Soil cations become increasingly soluble and available to plants as the exchangeable % increases. The goal is to maintain adequate amounts of nutrients for plant uptake while minimizing nutrient leaching loss. Optimum base saturation percentages recommended for a healthy growing condition should be 3-7% Potassium, 10-15% Magnesium, 65-75% Calcium. You will notice the calcium percentage is low and magnesium is high in clay soils. So the percentage stated above is the goal for a healthy soil. This can often be accomplished with a healthy application of calcium often found in the form of lime (if soil pH is below 7) or gypsum (if soil pH is above 7)