How to Grow Geraniums in Greenhouses

Geranium is a botanical genus containing 422 different species of annual, biennial and perennial flowering plants that are prized for their deep green foliage and vibrant blossom clusters. Native to South Africa, geraniums can be grown outdoors successfully in United States Department of Agriculture (USDA) plant hardiness zones 4 through 9. Geraniums also make excellent greenhouse plants. With proper care, greenhouse geraniums can grow from a simple cutting to a blooming plant in approximately eight weeks.

Difficulty:

Moderately Easy

Instructions

Things You’ll Need

• Sterile potting soil
• Sphagnum peat moss
• Well-rotted compost
• Perlite
• 6-inch deep planting tray
• Gardening knife
• 15-15-15 fertilizer

1. Combine equal parts sterile potting soil, sphagnum peat moss, well-rotted compost and perlite to create a loose, well-draining growing medium for your geraniums that is rich with organic materials. Pour the growing medium into a planting container that is at least 6 inches deep.
2. Harvest geranium cuttings from a mature, healthy plant; the best time to do this is in the morning. Use a sharpened and sterilized gardening knife to take several 3-inch cuttings from the plant. Make sure that each geranium cutting has at least two maturing leaves.
3. Stick the geranium cuttings into the growing medium a 1/2 inch deep. Space the cuttings at least 2 inches apart to allow air to circulate freely around the plants.
4. Keep the temperature of the greenhouse between 75 and 80 degrees Fahrenheit during the day to encourage healthy root, foliage and flower production. Lower the temperature of the greenhouse to between 60 and 62 at night to stimulate rapid root production, according to the Alabama Cooperative Extension System.
5. Water the geranium cuttings generously after planting to thoroughly moisten their growing medium. Check the moisture of the growing medium every two to three days and water as often as is required to maintain soil that is evenly moist, but never soggy or waterlogged.
6. Wait until the geranium cuttings form roots before fertilizing them for the first time. Once the cuttings have rooted, fertilize your geraniums weekly with a water-soluble 15-15-15 fertilizer. Dilute the fertilizer application to half-strength and apply according to the directions on the product label.

Tips & Warnings

• Mist your geraniums each day with room temperature water from a spray bottle to provide them with much-needed humidity. Do this in the early morning to reduce the risk of foliar diseases.

• Geraniums are often troubled by pests such as aphids, spider mites, whiteflies, fungus gnats and caterpillars. If the health of your geraniums begins to suffer due to insect pests, treat the plants with a garden insecticide product to correct the problem.