With their deep green foliage and large clusters of showy blossoms, potted geraniums add splashes of color whoever they are placed. Plants exist in a wide range of bloom colors from white to orange, red and violet. Two geranium species dominate commercial sales: the common geranium (Pelargonium x hortorum) with rounded, velvety leaves, and the ivy geranium (Pelargonium peltatum), which produces glossy, pointed leaves. Common geraniums grow upright in pots while ivy geraniums cascade from hanging baskets or planters.
Plant in Full Sun
Grow geraniums in fertile, well-drained potting soil that has plenty of organic matter. They are grown as annuals in U.S. Department of Agriculture hardiness zones 3 through 9 and can be grown as perennials in USDA zones above 9. Make sure the drainage holes in the containers are not blocked. Keep plants in an area where they get full sun in the morning and light shade in the afternoon. Geraniums generally grow to about 15 inches tall. Once the plant starts blooming, pinch off faded flowers to encourage the plant to keep producing blooms.
Fertilize with a slow-release 20-20-20 granular fertilizer once in the spring. Alternatively, apply a liquid 20-20-20 fertilizer in the spring, midsummer and late summer. Avoid overfertilizing. Water the plants when the potting soil feels slightly dry to the touch. Avoid getting water on the leaves; apply water directly to the soil instead. Be careful not to overwater geraniums.
Hot Weather Problems
Geraniums do best at temperatures below 70 degrees Fahrenheit. Geraniums that are being grown outdoors stop blooming during intense heat waves, a condition called "heat check." They normally will resume blooming once temperatures go back down. Plant breeders offer heat-tolerant geranium varieties in an effort to combat this issue. Geraniums are very resistant to insect pests and diseases, so pesticides, fungicides and similar products normally are not needed.
Where geraniums are grown as annuals, pruning is simply a matter of trimming dead and brown leaves and trimming away unhealthy stems that don't feel firm when gently squeezed. Before pruning, always sterilize pruning tools by dipping them in disinfectant. If you will be keeping geraniums through the winter, prune them in late fall or just before you bring them indoors. Prune the plant back by one-third to one-half, concentrating on snipping off woody or leggy stems.
Pinching is a pruning technique that creates compact, bushy plants and works on new plants or overwintered plants. Pinch geraniums in spring once the plant's growth starts taking off. Pinch 1/4 inch to 1/2 inch off the end of each stem with your fingertips or snips. The plant will grow two new branches off the end of each stem.