Geraniums are showy flowering plants that come in a wide variety of colors, including pink, blue, white and lavender. They have single or double flowers (two layers of petals instead of one) and variegated or scented leaves. Geraniums love sunlight and will grow in most soil types, but cannot tolerate freezing temperatures. To carry geraniums over the winter in Illinois, dig them up before the fall frost and keep them indoors until spring planting.
Choose a planting site that will offer eight or more hours of sunlight every day, as suggested by the Department of Horticultural Science at the University of Minnesota Extension.
Cultivate the soil in the planting area. Use a garden fork or shovel to turn the soil to a depth of between 8 and 10 inches.
Spread out a 1-inch layer of compost, peat moss or perlite over the planting area. Then, with a shovel or garden fork work that organic matter into the soil thoroughly. It is important to use one of these soil amendments for the heavy clay soils common in northern Illinois. This organic matter improves drainage and prevents geraniums from dying of a soggy root system.
Dig planting holes for the geraniums that are approximately the same width and depth as the planting pots. Each planting hole should be between 12 and 14 inches apart. Do not plant geraniums until the night air reaches 50 degrees F. and the soil temperature reaches approximately 60 F., approximately May 20th in Illinois.
Place a geranium into one of the planting holes. Then, fill the hole full of soil. Water each of the geraniums with a starter solution plant food that is high in phosphorus, such as 3-10-1, to promote vigorous root growth. Follow the instructions as specified on the product's label.
Fertilize each of the geraniums every three weeks. Mix into 1 gallon of water 2 tsps. of 20-20-20 water soluble fertilizer. Water the geraniums when the soil feels dry to the touch 1 inch below the surface of the soil.
Remove all faded or dead geranium blossoms to encourage new blossoms. Clip the faded or dead blossoms off at the base of their stems.
Remove the geraniums for over-wintering before the first fall frost to keep them alive until spring. Fall frost times vary, but they are approximately October 7 in northern Illinois and October 21 in southern Illinois. Dig up the entire root system and gently shake off any excess soil. Cut the germaniums back to about one-half their height.
Fill up 6-inch wide pots to about one-half full with potting mix. Set each geranium into the pot and scoop in potting mix to fill. Set the pots near a light-filled window. Keep the temperature within a range of 65 to 70 F. during the day, and between 55 to 60 F. at night. When the soil in any of the pots feels dry, provide each geranium with approximately 1 1/2 to 2 cups of water. Plant the geraniums in your garden the following spring.