Geraniums have been a popular bedding plant for many years. Plants traditionally are grown from cuttings. In recent years, however, seed-grown hybrid geraniums have become popular.
The popularity of seed-grown geraniums has increased because they often outperform the older geranium varieties propagated from cuttings. The new seed-grown hybrid geraniums possess excellent vigor, heat tolerance, disease resistance, and are free-blooming.
Geraniums are easy to grow from seed. However, they are rather slow growing. Sow seed in mid- to late January to produce flowering plants for spring. Flowering occurs approximately 12 to 16 weeks after sowing. Suggested seed-grown geraniums for Iowa include varieties in the Orbit and Sprinter 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.
A commercially prepared medium, such as Jiffy Mix, is a good germination medium. Gardeners can prepare their own medium by mixing equal parts sphagnum peat and vermiculite. 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 damping-off, containers used for starting seed should be clean and have adequate drainage. Previously used containers should be washed in soapy water, 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 several 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. To insure a uniform moisture level during the germination period, cover the container with clear plastic.
Set the container in bright light, but out of direct sunlight. Extremely high temperatures may develop if the covered container is set in direct sunlight. These high temperatures may adversely affect seed germination. The temperature of the medium during germination should be 75 degrees. With favorable temperature and moisture levels, the seed may start to germinate in five to seven days. However, some seed may not come up for three to four weeks. Remove the plastic covering as soon as germination occurs.
Transplant seedlings into individual containers when the first true set of leaves appears. Handle the small seedlings by their leaves since the small, thin stems break easily. Insert seedlings to the base of the seed leaves, called cotyledons, when transplanting. An excellent growing medium for geraniums consists of one part soil, two parts peat, and two parts perlite. The soil mix should be pasteurized before use. To pasteurize a soil mix, lightly moisten the material, place in a shallow baking pan, and bake in the oven at 180 degrees for 30 minutes. Cool the soil mixture before using. For best results, grow seedlings under fluorescent lights. The lights should be no more than 4 to 6 inches above the growing plants. Leave the lights on 12 to 16 hours per day. If supplemental lighting is unavailable, place the plants in a sunny south window. Geraniums become tall and spindly when grown without sufficient light. Pinch out the shoot tips of spindly plants to encourage branching.
Ideal growing temperatures for geraniums are 70 to 75 degrees during the day and 60 to 65 degrees at night. Thoroughly water geraniums when the soil surface is dry to the touch. Fertilize weekly with a one-quarter strength houseplant fertilizer. Harden or condition the plants outdoors for seven to ten days before planting into the garden. Plant geraniums outdoors when the danger of frost has passed. Geraniums can be planted outdoors in early May in southern Iowa, mid-May in central and northern portions of the state.
This article originally appeared in the January 13, 1995 issue, p. 4.