Garden geraniums (Pelargonium × hortorum) are one of the most dependable bedding and container plants around, grown for their rounded, often horseshoe-zoned leaves and tight clusters of red, pink, white, or salmon flowers that keep coming from spring until frost. What garden centers sell as "geranium" is technically a Pelargonium, a South African native in the Geraniaceae family; true Geranium species, usually sold as cranesbill or hardy geranium, are a related but distinct perennial genus, and the two names get confused constantly even though the plants behave quite differently in the garden. In Kentucky's zone 6b, Pelargonium has no winter hardiness outdoors and is grown as a tender annual, though it's easy enough to carry plants over indoors if you'd rather not buy new ones every spring. It asks for little beyond full sun, routine deadheading, and soil or potting mix that drains well. Few bedding plants give back as much color for as little fuss.
Sowing and planting
Most gardeners start geraniums from nursery transplants rather than seed, since named zonal and ivy varieties are typically propagated from cuttings and don't come true from seed. Seed-grown types exist and are widely sold, but they need an early indoor start, 12 to 14 weeks before your last frost date, under bright light and warm conditions to bloom on schedule by planting-out time; most home gardeners find it simpler to buy started plants in spring instead. Whichever route you take, wait until nighttime temperatures stay reliably above 50°F (10°C) before setting plants outside; in zone 6b that generally means mid-to-late May, after the last frost has safely passed. Geraniums planted into cold, wet soil too early sulk and are more prone to stem and root rot than plants set out once the ground has warmed. Space plants about 12 inches (30 cm) apart in a bed with full sun and well-drained soil, or set them at similar spacing in mixed containers, and water thoroughly after planting to settle the roots in.
Growing on
Water geraniums deeply once the top inch or so of soil has dried out, then let the soil dry down again before watering a second time; consistently soggy soil, especially in containers with poor drainage, causes root and stem rot faster than almost anything else affects this plant. Feed lightly with a balanced fertilizer every few weeks through the growing season, easing off in late summer so growth doesn't stay too soft and tender heading into fall. Pinch young plants back by an inch or two early in the season to encourage branching; this produces a fuller, bushier plant rather than a handful of leggy stems with flowers only at the tips. Deadhead spent flower clusters regularly, snapping or cutting the entire flower stalk off down at its base once the blooms fade. This single habit matters more than almost anything else you can do for a geranium: a plant deadheaded consistently will flower far more heavily over the season than one left to set seed on its own, since seed formation signals the plant to slow down and stop producing new buds.
Harvesting
Geranium flower clusters hold up reasonably well in a vase for a few days, so there's no harm in cutting a few stems for a short indoor arrangement, though the blooms are more often enjoyed in place in the bed or pot than brought inside. The real ongoing work is deadheading rather than cutting: removing spent flower heads as soon as they fade redirects the plant's energy into new buds instead of seed production, and this is what keeps a geranium blooming steadily through a long Kentucky summer instead of tapering off by midseason. Before the first hard frost arrives, decide whether you want to carry plants through winter rather than buy new ones next spring. You can pot up whole plants and move them to a bright, cool windowsill indoors, where they'll grow slowly over winter and can go back outside once the last frost has passed; or take four-to-six-inch cuttings in late summer, root them in fresh potting mix, and overwinter the young rooted cuttings indoors instead of trying to keep the larger parent plant alive and tidy all winter.
Problems and pests
Flowers turning brown and mushy in humid weather
Botrytis blight (gray mold) attacks geranium flowers, and sometimes leaves, during stretches of humid or rainy weather, leaving blooms slimy and gray-brown almost overnight. Remove affected flowers and any fallen petals promptly, and space plants to allow good airflow between them; watering overhead late in the day keeps foliage wet longer and makes the problem worse.
Water-soaked spots on leaves followed by collapsing stems
Bacterial leaf spot and stem rot, caused by a Xanthomonas bacterium, show up as small, dark, water-soaked spots on leaves that enlarge and can eventually wilt and collapse entire stems. There's no cure once it's established in a plant; remove and discard infected plants rather than composting them, and avoid overhead watering, which splashes the bacteria from leaf to leaf.
Buds chewed out before they can open
Geranium budworm, the caterpillar of a small moth, bores into developing flower buds and eats them from the inside, leaving ragged holes and buds that never open. Check plants in the evening when the caterpillars are active and easier to spot, hand-pick any you find, and remove damaged buds to reduce the next generation.
Small insects clustered on new growth
Aphids cluster on tender new shoots and flower buds, stunting growth and leaving a sticky residue on nearby leaves. A strong spray of water knocks most of them off the plant, and insecticidal soap handles persistent infestations without harming the beneficial insects that help keep them in check.
Small corky or water-soaked bumps on the undersides of leaves
Edema is a physiological problem rather than a disease or pest, caused when a plant's roots take up more water than its leaves can use, most often during cool, cloudy, humid stretches. Cut back on watering and improve air circulation around the plant; the damaged leaf tissue itself won't heal, but new growth that follows should come in unaffected.
Varieties worth growing
- Maverick series – A compact, uniform zonal type bred for bedding displays, available in a wide range of flower colors.
- Americana series – Large, dense flower clusters on a vigorous, weather-tolerant plant, a standard choice for mass plantings.
- Pinto series – A reliable seed-grown zonal type that blooms earlier from seed than many older varieties, good for gardeners starting their own plants.
- Summer Showers – A trailing ivy geranium well suited to hanging baskets and window boxes, with smaller, glossier leaves than the upright zonal types.
- Calliope series – An interspecific geranium bred for heat tolerance and continuous bloom, holding up especially well through Kentucky's hot, humid summers.
- Martha Washington (regal) types – Grown more for large, ruffled, bicolor blooms than for season-long bedding performance; they prefer cooler conditions and often struggle once Kentucky summer heat sets in.