Check garden mum roots for stress

Many parts of the country are experiencing warmer than normal temperatures. Some areas are also receiving very little rain.

Univ. of Mass. floriculture extension specialists Tina Smith and Paul Lopes and Univ. of Conn. extension horticulture and greenhouse IPM specialist Leanne Pundt advise growers of garden mums to monitor the root health of their plants. Select sample plants, remove them from their pots and examine the roots carefully. Symptoms of poor root health are blackened or rotted roots or lack of roots.

Pythium aphanidermatum is the species of Pythium that most commonly causes root rot losses to mums in recent years. The pathogen thrives in hot, summer weather.

Avoid allowing water to sit around containers, deep planting mum cuttings or overwatering. Provide even moisture and avoid high electrical conductivity values. Any root stress may open the plant up to Pythium attack.

Soil tests of chrysanthemum crops should be done regularly. Plants fertilized with controlled-release fertilizer may have high soluble salts and ammonium levels due to the recent hot temperatures. Very hot weather over an extended period of time can cause controlled-release fertilizer to release early, burn roots and weaken the plants.

Soil temperature is a primary factor affecting release of fertilizer from the controlled-release prills. If there are few roots, the growing medium remains saturated for a longer period of time. Once plants are stressed, root diseases take hold and cause a secondary problem.

Another problem that can occur is overwatering during hot periods. The controlled-release fertilizer releases but leaches out, leaving plants nutrient deficient with hardened growth.

The preceding article was originally published in Greenhouse Management magazine.