The vibrant bedding plants commonly called geraniums are members of the genus Pelargonium, tender perennials native to South Africa. They are grown as annuals in temperate regions because they cannot survive freezing temperatures. Successfully overwintering them indoors is a practical way to preserve favored varieties and ensure they thrive again the following spring. This process requires precise timing and specific preparation to transition the plants indoors.
Identifying the Critical Timing
The timing for moving geraniums indoors depends on local climate conditions, as they are highly sensitive to frost. Waiting until the first hard freeze is often too late. Move the plants inside well before temperatures drop consistently below 40–50°F (4–10°C) at night.
Monitoring the long-range forecast is the most reliable method. A single night near freezing can significantly damage the foliage and root structure. Bringing the plants inside a few weeks before the anticipated first frost allows them to adjust smoothly to the reduced indoor light and humidity.
Preparation for Indoor Transition
Moving garden plants directly indoors risks introducing pests and diseases. Before the transition, thoroughly clean and prune the geraniums to prevent contamination. Pruning involves removing one-third to one-half of the foliage and stems.
This reduction minimizes shock, reduces the surface area where pests can hide, and makes the plant a manageable size. Meticulously inspect the plant for pests like aphids, whiteflies, or spider mites, paying special attention to the undersides of the leaves and stem junctions. For protection, spray the entire plant with an insecticidal soap or Neem oil solution before moving indoors.
Clean the outside of the container, removing soil, debris, or insect egg masses clinging to the pot. Once inside, place the geraniums in a temporary quarantine area away from other houseplants for one to two weeks. This isolation allows monitoring for overlooked pests that may emerge under warmer, drier indoor conditions.
Choosing an Overwintering Strategy
Gardeners use two primary strategies for preserving geraniums over the winter, depending on available space and desired outcome. The first is maintaining the plant in active growth, treating it as a houseplant. This requires placing the plant in a location with abundant light, such as a south-facing window, or supplementing with artificial grow lights for 12 to 16 hours daily.
The ideal temperature for active growth is 60–65°F (15–18°C). Water plants only when the top inch of soil feels dry. This cooler temperature prevents the plant from becoming leggy and weak, common when light levels are insufficient. Active growth plants require occasional light pruning, called “pinching,” to maintain a compact shape and encourage branching.
The second method involves storing the plant in a dormant or semi-dormant state, ideal when space or light is limited. Geraniums are stored bare-root or in their pots in a cool, dark, dry location, such as an unheated basement or garage, where temperatures remain between 45 and 50°F (7–10°C). For the bare-root method, dig up the plants, shake soil off the roots, and place them in a paper bag or hang them upside down.
Dormant plants need little moisture; watering should be nearly eliminated to prevent fungal issues and discourage premature growth. Bare-root plants can be checked monthly; if roots appear shriveled, a light misting or brief soak in lukewarm water will rehydrate them. Potted, dormant plants should receive a tablespoon or two of water every four to six weeks to sustain life without encouraging active growth.
Spring Reawakening and Acclimation
The final phase begins in late winter or early spring, approximately six to eight weeks before the average last frost date. Dormant plants must be brought out of storage, and bare-root specimens should be potted into fresh, well-draining soil. This is the time for heavy pruning, cutting back all stems to firm, green tissue, often removing up to two-thirds of the plant material.
Once pruned and potted, place the geraniums in a bright, warm location and water them thoroughly to signal the end of dormancy. New growth will emerge within a few weeks. Once new foliage appears, introduce a weak solution of balanced liquid fertilizer. The focus is building the plant’s strength for the move back outside.
Before permanently relocating the geraniums to the garden, they must undergo “hardening off,” which slowly acclimates them to the outdoor elements. Over 7 to 10 days, gradually expose the plants to increasing amounts of direct sunlight, wind, and cooler temperatures. Start with a few hours in a sheltered, shady spot, and incrementally increase exposure daily to prevent sun scald and environmental shock.