July/August 2000

Gardeners Information Service

Rotting Begonias

My tuberous begonias have been blooming non-stop in hanging baskets for at least 10 years. Now the stems have started to rot and break off. The soil doesn't seem too wet. What am I doing wrong? -M.W., Wausau, Wisconsin

Your plants could be infected with a fungus that causes stem rot, a common problem with tuberous begonias that is usually associated with over-watering or planting the tubers too deep. The tubers should be covered with only half an inch of light potting soil, and the soil should be allowed to dry out a bit between waterings. Keeping the plant in a location where it receives good air circulation is helpful, and good plant hygiene is essential. Remove spent flowers before they fall into the foliage, where they can encourage fungal growth.

However, 10 years may be about as much as you can expect out of your tuberous begonias; the plants may simply be displaying the stress of old age. In this case, new tubers are the answer. Although tuberous begonias can be overwintered in their pots, it may be better to remove the tubers in autumn and put them in a sunny, airy location to "ripen."  When the stems and leaves have dried, clean the tubers, dust them with a fungicide, and store them in dry sand or peat moss at about 45 degrees Fahrenheit until it's time to plant them again next spring. 

Controlling Earwigs

Earwigs seem to be eating everything in my garden. Are there any synthetic or natural controls? -H.E., Arlington, Virginia

Earwigs are omnivorous-they eat plants, other insects, and decaying organic matter-but the damage they cause to garden plants is usually negligible. In fact, they are predators and often help control populations of far more destructive plant feeders such as aphids, nematodes, and mites. Night-feeding earwigs are sometimes blamed for injury that other pests have caused, because they like to hide in damaged plant tissues during the day. There's no reason to control earwigs unless you are sure they are responsible for unacceptable plant damage. In that case, you can keep them in check with insecticidal soap, which is available in most garden centers and hardware stores.

Non-flowering Hydrangea

My big-leaf hydrangeas aren't producing flowers. Any suggestions on how I can encourage them to bloom? -S.M., Raytown, Missouri

The most common reasons for a lack of flowering in hydrangeas are that flower buds are removed by pruning or they are killed by cold. Big-leaf hydrangeas (Hydrangea macrophylla) produce most of their flowers on the previous season's growth. In areas with mild winters, pruning should be done immediately after flowering.

In cooler regions such as yours, low winter temperatures or late spring frosts can kill flower buds. Old flowers left on the plant over winter can provide a measure of insulation from cold, but obviously that's not going to help your situation. Try setting up a screen of burlap around the hydrangea this winter to give it some protection. One other possibility for a lack of flowers is over-fertilization, which can cause the plant to grow foliage at the expense of blooms. If you think this may be the problem, cut back on fertilization and try switching to a fertilizer with a higher ratio of potassium and phosphorus in relation to nitrogen.     

William May, Gardeners Information Service, and Marianne Polito, Gardeners Information Service Manager