What Kind of Soil Kills Plants?

Compacted Soils

• Compacted soils are those that have been pounded down due to construction or heavy foot traffic. Clay soils are more likely to become compacted than sand. Compacted soils kill plants in two ways: Plants' roots can't spread in the soil to get nutrients and oxygen, and water doesn't drain well, suffocating plants. Fixing compacted soils is difficult and usually involves replacing the soil or building raised beds.

Toxic Plants

• Certain plants have allelopathic qualities, meaning they produce substances that are toxic to other plants. Black walnut trees are the most notable, although pecan, butternut and English walnut also may produce toxic substances. Black walnut trees produce juglone in leaves and stems, although the most concentrated amounts are found in the roots, where they are released and spread through the soil. The roots may spread 30 feet or more underground, potentially contaminating soil over a wide area. Some plants are more sensitive to juglone than others.

Clay Soils

• Heavy clay soils hold nutrients and water well, but they do not drain, essentially suffocating plants by depriving them of oxygen. Some plants tolerate clay soils better than others. To improve clay soils, till manure, compost and peat moss into the soil in the fall or spring and use organic mulches that decompose slowly. Do not till the soil while it's wet, because that results in hard, compacted soil. Select plant varieties such as lilacs, barberries, hydrangeas, honey locusts and crab apples that tolerate clay soils.

Saline Soils

• Salty soils limit plants' ability to absorb water, resulting in reduced growth, plant burn and poor seed germination and fruit yield. Saline soils are caused by poor drainage, de-icing salts, dry conditions or excessive fertilizers. Leach soils with water to reduce salt content, and avoid manures or de-icing salts.