Geraniums, part of the Pelargonium family, are popular indoors and out. With several hundred varieties within the species. each geranium is different, showing hundreds of color variations, petal sizes and shapes. Geraniums require fertilizer to sustain their beautiful flowers, so learn how to best fertilize your variety.
Apply 2 pounds of 10-10-10 or 4 pounds of 5-10-15 fertilizer per 1,000 square feet for outdoor geranium gardens. Apply in the spring, and apply a second, half dose, in late July.
Apply water to the dry fertilizer in outdoor gardens to sink it into the soil. An alternative to the dry fertilizer in outdoor geranium gardens is to use 2 level tsp. of water-soluble 20-20-20 fertilizer in one gallon of water and apply every 3 weeks. Do not use both dry and water-soluble in the same garden.
Apply fertilizer to indoor geraniums sparingly. Indoor soil mixes of 1 part soil, 1 part sand and 1 part peat will not require fertilization until after 3 months. Use 1 tsp. of 20-20-20 water-soluble fertilizer mixed into 1 gallon of water after the three-month period and apply again every two months. Fertilize during growing periods only.