Geraniums (Pelargonium spp.) are reliable plants that add bright color to the garden from late spring until the first frost in autumn. Although geraniums are often grown as annuals, they're perennial in U.S. Department of Agriculture plant hardiness zones 9 and 10. While geraniums are sturdy, disease-resistant plants, they are sometimes affected by rot, which is easy to recognize by stunted and yellowing growth and a brown or black, soggy, waterlogged appearance at the soil line. A badly rotted plant displays decayed, shriveled, water-soaked roots. Prevention is critical because once a plant is affected by rot, death soon follows.
Plant a potted geranium in a container or hanging basket with a drainage hole in the bottom. Without drainage, the plant will develop rot quickly.
Place a geranium where the plant is exposed to at least eight hours of sunlight per day. Geraniums aren't as healthy and don't flower well in shady conditions. Ivy geranium, which prefers mild temperatures and afternoon shade, is an exception.
Allow 12 to 18 inches between each plant. Don't crowd geraniums because overcrowding limits air circulation and increases the chance of developing rot.
Avoid excessive feeding because too much fertilizer makes geraniums weak, floppy and more prone to disease. Feed the plants at planting time and again in midsummer, using a general-purpose, 10-10-10 or 5-10-5 garden fertilizer at a rate of 3 tablespoons of dry fertilizer for each plant. Alternatively, use a water-soluble fertilizer every three weeks. Mix the fertilizer at a rate of 2 teaspoons in 1 gallon of water.
Water potted geraniums until water drips through the drainage hole; then, let the soil dry slightly before watering again. Similarly, water bedding plants to a depth of 6 inches, and let the top of the soil dry before the next watering. Never water if the soil feels moist and cool, but don't allow the soil to become so dry that the plant wilts. Periods of wilting following by heavy watering result in poor growth and possible rot.
Keep water off the foliage as much as possible because wet leaves place geraniums in danger of rot. Use a garden hose to water at the base of the plant instead.
Remove faded flowers and dry leaves throughout the season to keep geraniums neat and disease-free. Additionally, removing spent flowers stimulates the plant to produce more blooms.