How to Grow Geranium from Seed
Choosing the Pots
Damping off is a common problem when starting plants from seed. Damping off is the collapse and death of seedlings due to fungal infection. To avoid disease, it's always best to purchase new pots for seed germination. The pots should be clean and have adequate drainage.
If you are going to reuse pots that previously contained seedlings, wash them in hot, soapy water and allow to air dry. In a large bucket, combine a solution of one part bleach to nine parts water. Soak the freshly washed pots in the solution for a few minutes. Allow to fully dry before use in planting.
Choosing the Planting Soil
Any commercial growing medium is good for geranium seed germination. You can make your own by mixing equal parts vermiculite and Sphagnum peat moss.
Starting the Seeds
Because geraniums have exceptionally hard seed coats that can inhibit germination, some gardeners prefer to scarify the seed coat prior to planting, which means to scratch the seed coat to cause tiny breaks.
Sow seeds in rows ¼" apart with 2" between rows. Lightly cover with 1/8" of medium. Water by partially dipping the pot in water until the surface is moist. Cover with plastic wrap and place in a sunny location with indirect sunlight.
Geraniums germinate most prolifically in soil that is about 75°F. Open the plastic covering sporadically to ensure that the temperature inside does not become too hot. Moisten as necessary as soil dries out.
Seedlings should begin to sprout within 7-14 days. As soon as seedlings appear, remove the plastic wrap. Place the seedlings in a sunny window. They are ready to transplant when the first set of true leaves appear.
Transplant the seedlings to individual pots with a soil intended for indoor containers. A good mix would contain potting soil, peat, and perlite. Move to the sunlight and water as needed.
It is best to harden off plants to acclimate them to the conditions out of doors prior to actually planting them. For geraniums, bring them out of doors, in their pots for seven consecutive days. Plant outdoors when the last frost has passed.