Geraniums enjoy the status of being one of the most common flowering houseplants. These plants thrive both indoors and out. These flowers make nice additions to flowerbeds, window boxes and patio planters. Hothouse environments provide an excellent atmosphere for starting geraniums from seed. Early establishment in a greenhouse supplies strong specimens for transplanting.
Clear out an area in your hothouse in January to prepare for geranium planting. Check your selected location's temperature with a thermometer. Since temperatures often vary within a hothouse, select an area that remains near 75 degrees Fahrenheit. Avoid starting geranium seeds in higher temperatures that negatively affect germination. Provide adequate space for your seed flat near a source of bright light. Avoid direct sunlight for germination of geranium seeds.
Purchase a commercial growing medium for starting seeds, or make your own medium by mixing equal amounts of vermiculite and sphagnum peat. Place the soil in a seed flat with adequate holes for drainage. Keep the soil about an inch below the rim of the flat. Tamp down the soil and water thoroughly. Allow the soil to absorb the water for a few hours.
Sow your geranium seeds in the damp soil by placing the seeds in rows about 2 to 3 inches apart. Cover the seeds with a fine layer of planting medium. Submerse the bottom of your seed flat in water to allow moisture to absorb through the drainage holes, into the seed flat. Once the surface of the flat shows signs of dampness, remove from the water. Cover the top of the seed flat with clear plastic and watch seeds germinate.
Transplant your seedlings into small pots after a few leaves appear on the small plants. Set the small seedlings into the soil to a level just below the bottom leaves. Plant the seedlings this deep to encourage healthy root development.
Set the transplanted seedlings under fluorescent lights in an area of your hothouse that maintains a heat level between 60 and 75 degrees. Water your geraniums whenever the surface of the soil feels dry to the touch. Transplant outdoors after all chance of frost has passed.