Pinch out the shoot tips of spindly plants to encourage branching. Ideal growing temperatures for geraniums are 70 to 75 degrees F during the day and 60 to 65 degrees F at night. Thoroughly water geraniums when the soil surface is dry to the touch. Fertilize every two weeks with a diluted fertilizer solution. Harden or acclimate the plants outdoors for 7 to 10 days before planting into the garden.
Plant geraniums outdoors when the danger of frost has passed.
Generally, mid-May is a safe planting time for geraniums in central Iowa. When starting plants from seed this winter, don't forget geraniums. While most gardeners purchase their geraniums from garden centers in the spring, growing them from seed is easy and fun.