The common garden flower known as the geranium is botanically a Pelargonium, a tender perennial grown as an annual in most climates. Starting these plants from seed offers a distinct advantage over purchasing mature plants, primarily through cost savings for mass plantings. Seed-starting also provides access to a much wider array of unique flower colors and varieties not typically available as young plants in garden centers. The process from sowing the seed to seeing the first flower typically takes 12 to 16 weeks.
Preparing for Seed Starting
Successful indoor starting begins with precise timing, typically 10 to 12 weeks before the final expected frost date in your region. This window ensures the seedlings are mature enough for the garden once outdoor temperatures are reliably warm. Select small containers or multi-cell trays that have drainage holes to prevent waterlogging and reduce the risk of fungal disease.
Fill your chosen containers with a sterile, soilless seed-starting mix, which provides a clean and fine texture for delicate root development. Proper preparation of the seeds encourages swift germination. The hard outer shell of Pelargonium seeds can be slightly scuffed (scarification) or soaked in warm water for up to 24 hours to help water penetrate the seed coat.
Sowing and Initial Germination
After preparing your seeds and moistening the starting mix, sow the seeds by placing them on the soil surface. Cover them lightly with approximately one-eighth of an inch of the seed mix or fine vermiculite. This shallow covering helps anchor the seed while allowing light to penetrate the surface.
Watering should be done carefully, preferably by setting the container in a tray of water for a few minutes to allow the soil to absorb moisture from the bottom up. This bottom-watering technique prevents the small seeds from being dislodged or washed away.
The ideal environment for germination requires a consistently warm temperature, between 70 and 75 degrees Fahrenheit. Achieving this temperature often necessitates the use of a specialized heat mat placed beneath the container. To maintain high humidity and consistent moisture, cover the entire tray with a clear plastic dome or plastic wrap. Seeds will begin to sprout within 3 to 21 days, and the covering must be removed immediately once the first shoots appear.
Caring for Young Seedlings
Once the seedlings have emerged, remove the humidity dome and move the plants to a cooler environment to encourage sturdy growth. The ideal temperature range is 70 to 75 degrees Fahrenheit during the day and 60 to 65 degrees Fahrenheit at night. This temperature differential helps prevent the seedlings from becoming long and spindly.
Supplemental light is required to prevent stretching, as a sunny window alone is often insufficient during winter months. Position a grow light source, such as a fluorescent or LED fixture, approximately four to six inches above the tops of the plants. Keep these lights running for 12 to 16 hours daily to mimic optimal growing conditions.
Begin a light fertilization schedule only after the seedlings develop their first set of true leaves. Use a diluted liquid fertilizer, mixed at about one-quarter of the recommended strength, applied once per week. When the seedlings have developed four to six true leaves, they are ready for “pricking out”—transplanting them into individual, slightly larger pots.
Handle the delicate seedlings gently by their leaves rather than their fragile stems during this process. The final step before moving them outside is called hardening off, a 7-to-10-day process of gradual acclimation. Start by placing the plants outdoors in a shaded, protected area for just a couple of hours, slowly increasing their exposure to direct sunlight, wind, and cooler overnight temperatures each day.
Transplanting and Ongoing Maintenance
The hardened-off Pelargoniums should only be transplanted into their final outdoor location after all danger of frost has passed. Choose a planting site that receives at least six hours of direct sunlight daily for the best flower production. The final soil should be well-drained and fertile, whether planting in the ground or in patio containers.
When planting multiple geraniums together, ensure adequate air circulation by spacing them approximately eight inches apart in a container or up to 18 inches in a garden bed. Watering needs should be met by thoroughly soaking the soil only when the surface feels dry to the touch. Allowing the soil to dry slightly between waterings is important, as these plants do not tolerate consistently soggy conditions.
Ongoing maintenance involves regular deadheading to encourage continuous blooming throughout the season. Although many modern seed varieties are self-cleaning, removing spent flower heads by snapping the entire stalk at the stem promotes a tidier appearance and directs energy toward new buds. Continue to feed the plants every two to three weeks during the active growth period using a balanced liquid fertilizer.