Potting Mix
Potting soil must provide drainage so the soil doesn't retain too much moisture. Packaged soil that contains perlite or vermiculite usually provides enough drainage. You can make your own mixture by combining 3 parts loam soil, 1 part peat moss and 1 part coarse sand or perlite. The perlite provides soil aeration and improved drainage, while the peat moss retains just enough moisture so the soil doesn't dry too quickly. Loam is rich in organic matter, which provides structure and some nutrients for the geranium roots.
Fertilizer
Packaged potting mixtures may contain some fertilizer, which is noted on the label, so they won't need fertilizer for the first four to six weeks after planting. Homemade mixes usually require regular fertilizer applications from the time of planting until the end of the growing season. Fertilize geraniums every seven to 14 days with a soluble 15-30-15 fertilizer. Watering the plant with a mixture of 1 teaspoon fertilizer combined with 1 gallon of water replenishes the nutrients in the soil. Check the dilution rates on the label as they vary among brands.
Planting
A geranium pot must contain at least one bottom drainage hole, otherwise moisture becomes trapped in even the best potting mix. Most geraniums grow well in an 8- to 10-inch-diameter pot, although some dwarf varieties may do well in slightly smaller containers. Moisten the potting mix thoroughly before planting the geranium and allow the excess water to drain from the soil for about 30 minutes after watering. When planting the geranium in the pot, set it at the same depth it was growing at in its nursery container.
Basic Care
Whether grown indoors or outside, potted geraniums require similar care. The plants need at least six hours of daily sun to ensure compact growth and plentiful flowers. Temperatures between 65 and 70 degrees Fahrenheit result in healthy plants, although geraniums can tolerate warmer weather. The plants need water when the top 1 inch of soil begins to dry. Indoor plants may only need to be watered once or twice a week, while the soil in outdoor pots dries more quickly and may need daily watering.