Geraniums (Pelargonium) have been a popular bedding plant for many years. Most gardeners purchase plants from garden centers and greenhouses. However, geraniums can also be grown from seeds. Seed-grown hybrid geraniums possess excellent vigor, heat tolerance, disease resistance, and are free-blooming.
Geranium seeds should be sown in early to mid-February to produce flowering plants for spring. Flowering occurs approximately 13 to 15 weeks after sowing.
Suggested seed-grown geraniums for Iowa include varieties (cultivars) in the Elite, Orbit, Maverick, and Multibloom Series. A series is a group of closely related cultivars with uniform characteristics, such as height, spread, and flowering habit. Generally, the only characteristic that varies within a series is flower color.
Excellent seed-starting media are commercially prepared soilless mixes, such as Jiffy Mix. Containers used for starting seeds should be clean and have drainage holes in the bottom. Previously used containers should be washed in soapy water and then disinfected by dipping in a solution containing one part chlorine bleach and nine parts water.
Sowing Seed and Germination
Fill the container with the germination medium to within 1 inch of the top. (If the germination medium is dry, moisten it before filling the container.) Lightly firm the medium. Sow the seeds in rows 2 to 3 inches apart and cover with an additional 1/8 inch of material. After sowing, water the medium by placing the container in a pan of warm water or by applying a fine spray to its surface. Cover the container with clear plastic food wrap or a clear plastic dome to insure uniform moisture levels during germination. Set the container in a warm (75°F) location. With favorable temperature and moisture levels, the geranium seeds should begin to germinate in 7 to 10 days.
Remove the plastic covering as soon as germination occurs. Place the seedlings in a sunny window or under lights. Plants grown in a window often become tall and spindly because of inadequate light. For best results, grow seedlings under fluorescent or LED lights. A standard high-output, full-spectrum plug-in shop fixture works well. Light fixtures should be no more than 4 to 6 inches above the seedlings and left on for 12 to 16 hours per day.
Using a well-drained commercial potting mix, transplant the seedlings into individual containers when their first true set of leaves appears. Place the transplanted seedlings under lights or in a sunny window. Ideal growing temperatures for geranium seedlings are temperatures of 70 to 75°F during the day and 60 to 65°F at night. Water the seedlings when the surface of the potting soil becomes dry to the touch. If using a commercial potting mix containing a slow-release fertilizer, fertilization probably won't be necessary. An application of a dilute fertilizer solution once every 2 weeks should be sufficient for those potting mixes that don't contain a slow-release fertilizer.
Hardening and Planting Outdoors
Harden or acclimate the plants outdoors for 7 to 10 days before planting into the garden. Initially, place the geraniums in a shady, protected location. Then gradually expose the plants to longer periods of sunlight. Plant the geraniums outdoors when the danger of frost has passed. In central Iowa, it's usually safe to plant geraniums outdoors in mid-May.