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.