Geraniums have been a popular bedding plant for many years. Plants are commonly grown from cuttings. However, geraniums also can be grown from seed. Seed-grown hybrid geraniums possess excellent vigor, heat tolerance, and disease resistance and they are free-blooming.
Geraniums are relatively easy to grow from seed; however, they are slow growing. Geranium seed 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 in the Orbit, Maverick, Multibloom, and Ringo 2000 series. A series is a group of closely related varieties with uniform characteristics, such as height, spread and flowering habit. Generally, the only characteristic that varies within a series is flower color.
Soilless mixes, such as Jiffy Mix and Redi-earth, are excellent germination media. During germination, damping-off of geranium seedlings can be a serious problem and is caused by various types of fungi that attack the seedlings and destroy them. To discourage fungal infection, containers used for starting seed should be clean and have adequate drainage. 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.
Fill the container with the germination medium to within 1/2 to 1 inch of the top. Firm the medium lightly, water thoroughly, and allow it to drain for 1 or 2 hours. Sow the seed in rows 2 to 3 inches apart and cover with about 1/8 inch of medium. After sowing, thoroughly water the medium by partially submersing the container in water. When the surface becomes wet, remove the container from the water and allow it to drain. The medium also can be moistened with a rubber bulb sprinkler. The sprinkler produces a gentle spray that won't wash the seed or potting mix. To ensure a uniform moisture level during the germination period, cover the container with a clear plastic dome or clear plastic food wrap.
Set the container in bright light, but out of direct sunlight. Excessive heat buildup may occur if the covered container is set in direct sunlight. The temperature of the medium during germination should be 70 to 75 F. With favorable temperature and moisture levels, the seed 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 fluorescent lights. Fluorescent lights should be no more than 6 to 8 inches above the seedlings and left on for 12 to 16 hours per day. Using a well-drained potting mix, transplant the seedlings into individual containers when their first true set of leaves is present. Handle the small seedlings by their leaves because the small, thin stems break easily. Insert seedlings to the base of the seed leaves (cotyledons) when transplanting.
For best results, grow seedlings under fluorescent lights. (A standard fluorescent shop fixture with one 40-Watt cool white and one 40-Watt warm white tube works fine.) Plants grown in a window often become tall and spindly because of inadequate light. Ideal growing temperatures for geraniums are 70 to 75 F during the day and 60 to 65 F at night. Thoroughly water geraniums when the soil surface is dry to the touch. Fertilize weekly with a one-quarter strength soluble houseplant fertilizer.
Harden or acclimate the plants outdoors for 7 to 10 days before planting in the garden. Initially, place the plants in a shady, protected location, and 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 around May 10.
This article originally appeared in the February 7, 2003 issue, p. 9.