Annual geraniums (Pelargonium spp.) are favorite bedding plants. Often planted in window boxes, they are reliable bloomers and beautify the home throughout the growing season. Geraniums, which require full sun, offer a good opportunity to look at the basics of photosynthesis. Annual geraniums are also called common, bedding, garden or zonal geraniums.
Photosynthesis is the process used by plants to convert carbon dioxide and water into chemical energy (sugar), using sunlight as energy. Photosynthesis occurs almost entirely in plant leaves, using chlorophyll in leaf cells. Chlorophyll is the chemical that makes plants green. After photosynthetic conversion, the plant uses sugar as the energy to drive all plant processes.
Plants cannot live without successful photosynthesis. In the garden, if anything interferes with the process, such as too much shade, malnutrition or disease, the plant will decline, eventually dying if the condition persists.
Geraniums should be planted in full sun. Give them moist, well-drained soil. Improvement of poor or compacted soils with organic matter improves drainage and water retention. It also naturally improves nutrition.
Soil pH should be slightly acidic, about 6.5. Given their rapid growth and abundant flowering, geraniums require regular feedings with a balanced fertilizer formulated for bedding plants. Balanced fertilizers have roughly equal amounts of nitrogen (N), phosphorus (P) and potassium (K). N-P-K ratios should be about 10-10-10 or 8-8-8.
Too much shade impedes photosynthesis. Give geraniums at least four-to-six hours of sunlight daily and follow space recommendations so plants don't shade each other. If soil pH is too acidic, below about 5.5, geraniums turn yellow because they can't fully absorb soil nutrients. This condition, chlorosis, inhibits photosynthesis because of chlorophyll deprivation. Moderate soil pH with lime to encourage better nutrient uptake.