Geraniums come in a range of colors, including pink, white, red and orange, and make for excellent bedding and potted plants, according to the University of Florida. These vigorously growing flower plants require regular fertilization to sustain their growth and blossom production. Fertilizer requirements vary, depending on the time of year and whether you’re growing the geraniums indoors or outdoors.
Fertilizer applied before geraniums are planted in their new outdoor flowerbeds helps ensure that a high level of nutrients is immediately available. Clemson University recommends using a 10-20-10 fertilizer, or one with a similar ratio of nutrients, at a rate of 1 lb. for every 100 square feet. Mix the fertilizer into the top 4 to 6 inches of bedding soil 14 days before you plan to plant your geraniums.
After the initial fertilizer application, regular follow-up doses of fertilizer help maintain the soil’s fertility to keep the geraniums growing and blooming all season long. For follow-up fertilization, North Carolina State University suggests spreading a basic 8-8-8 or 10-10-10 fertilizer at a rate of 2 lbs. for every 100 square feet. Apply the fertilizer every four to six weeks, suggests the university.
Unlike outdoor geraniums, indoor geraniums don’t need as much fertilization. The University of Minnesota states that most potting soil mixes contain enough nutrients to start the flowering plants. After 60 to 90 days, apply the first fertilizer dose. The university suggests using a water-soluble 20-20-20 fertilizer product by mixing 1 tsp. in a gallon of water and using the enriched water to thoroughly soak the potting substrate.
Apply the second fertilizer dose for the indoor flower plants in the fall, as the seasons shift and the geraniums start to naturally reduce their rate of growth and blossoming. The University of Florida recommends trimming back the plants–cut back the branches by no more than 30 percent of their original length–and immediately applying a basic water-soluble fertilizer. This reinvigorates the geranium plant and boosts its growth and flower production.