The main soil nutrients plants require for healthy development are nitrogen, phosphorus and potassium. These three basic nutrients are supplied by either organic or inorganic fertilizers. Organic fertilizers, such as manure and compost, supply nutrients in less concentrated amounts than commercial inorganic fertilizers. Organic fertilizers improve soil structure, supply beneficial microbes and trace nutrients, and also reduce some of the problems associated with chemical fertilizers.
Over-fertilization may lead to lake and groundwater pollution. Over a large area, many homeowners and businesses using fertilizers contribute to runoff that can cause excessive nutrient levels in lakes and streams, producing algae and water weed growth. Following fertilizer label instructions closely and careful cleanup of spilled fertilizer from surfaces such as driveways and roadways reduces the amount of chemicals that wash into storm drains. Organic composts improve the soil texture, increasing its ability to hold onto water and nutrients, which reduces the need for chemical fertilizers.
Excessive fertilizer use can lead to "burn," with symptoms such as spots, streaks or a uniformly brown appearance of affected plants. Fertilizer applied to wet grasses may lead to burn if not immediately rinsed off, according to West Virginia University Extension. Some plants are burned by too much fertilizer, whether from manure or chemical sources. Wildflowers, seedling vegetables and rock garden plants are particularly susceptible to fertilizer burn. Cultivated ornamental and fruiting plants and turf grasses are typically heavy feeders. Supplying fertilizer to the garden soil is recommended over spraying fertilizer on the leaves.
Soil pH (the measure of acidity and alkalinity) determines how well plants take up and use available nutrients. If the soil pH is too high (alkaline soil), nutrients become insoluble and unavailable, which causes chlorosis, or loss of green pigment. Chlorotic plants grow slowly and have yellow foliage between the leaf veins. Obtain a soil test analysis from your local county extension if necessary to determine your soil's pH level.