Geraniums are perfectly suited for window boxes. Available in a range of bright colors in both double and single blooms and either upright and trailing varieties, geraniums will add style and pizazz to your outdoor living environment. Geraniums are sturdy plants that will survive even with occasional neglect, as long as they are planted where they will be exposed to plenty of bright sunshine.
Use window boxes that are at least 8 to 12 inches across, which will allow adequate space for the geranium's roots. Be sure the window boxes have drainage holes in the bottom.
Place the window boxes under a window where the plants will be exposed to full sunlight for at least six to eight hours each day. Attach the window boxes to a strong support. The window boxes will be much heavier when the potting soil is wet.
Fill the window boxes with an all-purpose commercial potting soil. Avoid garden soil, which will be too heavy and will become compacted when wet. Be sure the window boxes have drainage holes in the bottom.
Arrange the geraniums on top of the potting soil, allowing at least 8 inches between each plant. Once the geraniums are arranged the way you like, use a trowel to dig a hole for each plant. Plant the geraniums and tamp the soil down lightly. Water the geraniums immediately.
Feed the geraniums once a month, using a water-soluble fertilizer for blooming plants. The fertilizer should be applied according to the directions on the package, except the solution should be diluted to half-strength.
Check the potting soil daily. Window boxes will dry out quickly and may need to be watered once daily during the summer.
Deadhead, or pinch off, spent geranium blooms to encourage the plants to continue blooming as long as possible. If the plants begin to appear long and leggy, pinch off the top of the plant to promote bushy, full growth. Pinch the stem just above a pair of leaves.