To apply a fertilizer, you must have a soil that will accept nutrients. If your soil will not accept fertilizer, you may have to amend, or alter, it so that it will. Your soil should not be too wet or too dry. Different plants need different kinds of fertilizer applied in a different manner. Research your plant or crop, and learn the pH of your soil; whether it is acidic or alkaline affects what nutrients it will accept.
Soil Too Dry
Nutrients must be in some form of solution for plants to use them. When the soil is too dry, it is difficult for the plant to accept the fertilizer. If the soil is extremely dry, do not fertilize.
Soil Too Wet
Soil that is too wet also has negative consequences. Plant roots, which take in the nutrients, need air. If the soil is too wet, the roots are smothered, unable to "breathe." Your plants need to be in soil that can drain properly. If your soil is clay, add organic matter to help it drain.
Fertilizer "burn" refers to the dehydration and browning of the roots or crown of the plant. The nitrogen found in most fertilizers sucks water from the plant tissues. Excess nitrogen beyond what a plant needs can cause fertilizer burn. The symptoms can appear within days or weeks.
If applied in sufficient amounts, plants can be burned by the nitrogen in ammonium nitrate, sewage sludge, compost and numerous other fertilizers. To wash out excess nitrogen, water your plants after you fertilize them.
Problems with Soil pH
Soils are described by their acidity or alkalinity. The pH of a soil affects its ability to accept nutrients, which is what fertilizers are. A pH soil rating of seven is neutral. Anything below seven is acid; anything above seven is alkaline. If soil pH is under six, the nitrogen, phosphorus, and potassium that a plants need is less available. If the pH is above 7.5, phosphorus, iron, and manganese are less available. Some plants like acid soil. Others need alkaline soil.
To be able to properly choose plants, you must know the pH of your soil. You can usually find out how to have it tested by contacting the agricultural extension service in your state. To make your soil more acidic, add sulfur or cottonseed oil. To make it more alkaline, add lime. The best advice is to choose plants that like a higher pH.
When the soil pH is too high, iron and other nutrients are changed into insoluble mineral salts that plants can't use. A lack of iron causes chlorosis, a loss of the green pigment of foliage, causing slow growth and yellow leaves. The pH can be lowered by adding cottonseed meal or sulfur.
Bacteria in commercial fertilizers, composts and manures eventually turn the nitrogen to nitrates that can leach into groundwater, streams and rivers. Phosphorus binds to topsoil particles, washing with them into surface water. Phosphorus stimulates the growth of algae in slow-moving streams, removing oxygen that fish need to survive.
Plants have evolved to take up nutrients through their roots, not through the fruit or leaves. Fertilizers have recently appeared on the market purporting to take in nutrients through the leaves. To some extent, these fertilizers can take in potassium, calcium and zinc, but fertilizer applied to the roots remains the nutrient of choice.