Potted geraniums (Pelargonium species) are excellent indoor plants and can be grown indoors throughout the year. They are typically available from March through June, and will flower continuously if provided with enough light in the home. Many new types are available, including vining and hanging basket cultivars. They can be purchased in various stages of growth and in many different types of containers.
- Zonal geraniums or Common Geraniums (Pelargonium x hortorum) usually have distinct leaf markings. They include selections with tri-colored leaves, silver leaves, leaves with white markings and fancy-leafed geraniums. Flower colors are usually pink, red or white.
- Ivy-leafed Geraniums (Pelargonium peltatum) are trailing in habit and have leaves that resemble ivy leaves. They are commonly used in hanging baskets and window boxes.
- Martha Washington Geraniums (Pelargonium x domesticum) are available from many florists during the winter months as flowering pot plants. They are not heat-tolerant and will not perform as well outdoors as the common geranium.
Soil Mix & Container: Plant geraniums in window boxes, tubs, hanging baskets or other large pot containers. Each container must have good drainage. The potting medium should be well-drained and high in organic matter. A good mixture might contain equal parts of garden loam, peat moss and coarse sand or perlite. Professionally prepared commercial soil mixes may also be satisfactory. You may have to try several before you find one that gives good results for your particular growing conditions.
Watering: Inspect your plant each day to make sure it has enough moisture. Geraniums respond favorably to having the soil dry out somewhat between each watering. Apply enough water so that some drains from the bottom of the container each time you water. Water only as needed, checking the soil for dryness to a depth of 4 to 6 inches.
Fertilizing: Soluble or slow-release fertilizers are best for container-grown plants. Fertilize semi-monthly from March through October. If plants are being grown where light intensity is low or indoors during the winter months, reduce the amount of fertilizer accordingly. Apply fertilizer according to directions on the label, and make sure that the soil is moist before applying.
Light & Temperature: Bright light is essential to keep geraniums in flower throughout the year. South- and west-facing windowsills are the best locations for geraniums, especially during the winter months. If strong, natural light is not available in the home, artificial light is acceptable. Satisfactory results can be obtained if the plants are placed 12 inches beneath a 40-watt, daylight, cool fluorescent bulb for 16 hours each day. Temperatures during the day of 65 to 70 ºF and around 55 ºF at night are ideal. Avoid placing geraniums in cold, hot or drafty areas.
Geraniums are not winter-hardy and must be brought inside before frost if you wish to keep them. Gardeners wishing to overwinter their geraniums can try several techniques. Before the first frost, dig large geraniums from the garden and plant in pots large enough to hold their root system. Discard any plants with evidence of insects or diseases. Cut back the top of the plant to 6 inches in height, and place in a sunny window. You can also take cuttings in the fall, and keep the small potted plants on a windowsill during the winter months. Transplant to the landscape or keep in pots once the danger of frost has passed.
Overwatering and high humidity may cause oedema, resulting in small, corky cell production on the leaves. Reduce watering and increase light levels to control this problem. Botrytis blossom blight can develop in cool, damp conditions. This disease causes premature fading and drying of flowers. Remove old flowers as soon as they start to fade, and provide good air circulation. Common insect pests include mealybugs, caterpillars, mites, whiteflies and aphids.
Information on how to grow geraniums outdoors is available in HGIC 1164, Geranium.