The common garden flower known as the geranium is actually a member of the Pelargonium genus, typically grown as an annual in most temperate climates. Determining the optimal time for planting these vibrant flowers depends entirely on the starting point: seeds, cuttings, or established transplants. The entire planting process is dictated by the plant’s extreme sensitivity to cold weather and frost.
Starting Geraniums Indoors
Gardeners who wish to grow geraniums from seed must begin early, typically 10 to 12 weeks before the average date of the last expected frost. Some cultivars may require up to 16 weeks of indoor growth to reach a robust size suitable for transplanting outside. Seeds should be sown in a sterile starting mix and maintained at a consistent soil temperature between 70 and 75 degrees Fahrenheit for successful germination.
Propagation via cuttings offers a faster path to an established plant, as the rooting process usually takes about six to eight weeks. Once the cuttings develop a strong root system, they can be potted into containers and grown under bright light until outdoor conditions are favorable. Starting plants indoors ensures they are mature enough to bloom immediately once the summer heat arrives, bypassing the slow initial growth period that occurs if sown directly into cold spring soil.
Outdoor Planting Timing
The final placement of geraniums into garden beds or permanent containers must be delayed until all danger of a late spring frost has completely passed. These plants are exceptionally tender, and even a brief exposure to freezing temperatures can cause significant, often fatal, damage. The critical timing milestone is the average last frost date for the specific climate.
Beyond the date of the last frost, consistently warm nighttime temperatures are required for geranium health and growth. Geraniums thrive when the air temperature remains above 50 degrees Fahrenheit, and ideally, above 55 degrees Fahrenheit during the overnight hours. When temperatures dip below this threshold, the plant’s growth rate slows dramatically, and prolonged exposure can lead to stress or reddish discoloration on the leaves.
Before any indoor-started or newly purchased greenhouse plants are permanently set out, they must undergo a process known as “hardening off.” This acclimation process takes 7 to 10 days and is necessary to prevent shock from the abrupt change in environment. The process involves progressively exposing the plants to outdoor conditions, starting with an hour or two in a shaded, sheltered location. Each day, the duration outside is increased, gradually introducing the plants to more direct sunlight and wind before their final planting.
Planting for Year-Round Container Care
Many gardeners choose to grow geraniums in containers, which allows for seasonal movement and extended plant life. For established plants that have been overwintered indoors, the timing for their return to the outdoor environment is the same as for new transplants. They should be moved back outside only after the threat of frost is gone and the nighttime temperatures are reliably staying above 50 degrees Fahrenheit.
Even these established plants require the hardening-off procedure to prevent sun scald and wind damage to the new, soft spring growth. Similarly, the timing for bringing container-grown geraniums inside in the fall is important for their survival. Plants should be moved to a protected location, such as a garage or basement, well before the first expected hard frost. Bringing them inside when the consistent nighttime temperature begins to fall below 55 degrees Fahrenheit helps ensure the plant remains healthy and avoids cold-induced stress before its winter rest.