Aster Macrophyllus Care

Water and Fertilizer

• Bigleaf aster benefits from watering during warm weather, whenever rainfall is less than 1 inch per week. Water to a depth of about 6 inches, then water again when the top of the soil feels slightly dry. Check the plant often, as both bone dry or sopping wet soil may impact flowering and cause the plant to drop leaves. Water at the base of the plant and keep the leaves as dry as possible because wet foliage places the plant at risk of mildew and other disease. Bigleaf aster requires no fertilizer.

Mulch

• An annual springtime application of mulch protects the roots and keeps the soil moist, preventing the need for frequent watering. Use a natural mulch such as bark chips, chopped leaves or pine needles. A 2- to 4-inch layer is beneficial; however, limit mulch to 3 inches or less if you notice slugs, because a thick layer of mulch creates a warm, moist, slug-friendly habitat. If you have a compost pile, enrich the soil with a thin layer of compost under the mulch.

Maintenance

• Bigleaf aster requires minimal maintenance to keep the plant healthy and looking its best. Pinching the tips of new plants once or twice in the spring forces the aster to branch out, creating a fuller, bushier plant. To encourage bigger blooms, thin a mature plant to six to eight shoots in the spring. Dividing the plant every two to three years revitalizes the plant and prevents the center from dying out. Remove blooms as soon as they wilt. Cut the plants to the ground in early winter or before new growth appears in early spring. Be sure to stake the plant if it becomes top-heavy.

Potential Problems

• Although bigleaf aster is relatively disease resistant, you can minimize the risk of mildew, rust and other diseases by proper watering and by providing ample space for air circulation around plants. Insecticidal soap spray is a safe and effective treatment for sap-sucking pests such as mites and aphids. Spray the plant thoroughly, coating both sides of the leaves, with a mixture of 2 teaspoons of commercial insecticidal soap in 1 quart of water. Increase the mixture to 2 1/2 tablespoons of soap for a severe infestation. Keeping the area around the plant clean and free of leaves and other plant debris helps discourage slugs. If you notice slugs or snails chewing holes in the leaves, apply a commercial slug bait. A light application -- 1 teaspoon per 1 square yard of planting space -- is sufficient.