The Effects of Fertilizers


People who love their plants often use fertilizers to help their plants grow strong and produce the maximum number of leaves, flowers, vegetables or fruit. Many brands of fertilizer are sold at garden supply stores for home gardeners, while large-scale farmers often use special fertilizers on their crops that promote plant growth and help to prevent diseases.

Types of Fertilizers

Two types of fertilizers exist: synthetic (chemical) and organic (natural). Chemical fertilizers often have a faster, more dramatic effect than organic fertilizers and are available at many types of stores. Organic fertilizers are also sold in liquid and granular form, but it's easy to make homemade compost that will nourish your plants without synthetic ingredients. Both types of fertilizer help plants to grow big, strong and healthy.

How Plants Get Nutrients

The way that plants receive their nutrients is different from the way humans get them. Although we call fertilizers "plant food," fertilizers only represent one of the methods plants use to get the vitamins, minerals and other nutrients they need to grow. If you look at plants that grow in the wild, they succeed in living long, healthy lives without the help of humans and the fertilizers they use on cultivated plants. Plants take advantage of sunlight by using a process called photosynthesis to manufacture carbohydrates to supply them with food. Fertilizers provide an artificial boost by giving plants extra nutrients that can make them grow faster or taller than their wild relatives.

What Fertilizer Contains

The three main ingredients of fertilizers are nitrogen, phosphorus and potassium. These elements are indicated on fertilizer packages by three numbers known as the N-P-K ratio. N stands for nitrogen, P stands for phosphorus and K stands for potassium. All three are essential plant nutrients and are contained in different ratios depending upon the fertilizer product and the specific use for which it is designed. A typical, balanced fertilizer contains an equal proportion of nitrogen, phosphorus and potassium. Often, other plant nutrients, such as minerals like iron or magnesium, are also contained in commercial fertilizers. If you make organic compost with lots of fresh, green plant materials, such as lawn trimmings, it will be high in nitrogen.

Effect of Nitrogen on Plant Growth

Nitrogen is one of the main nutrients included in fertilizers, whether they are synthetic or organic in nature. Plants use nitrogen to form green, leafy growth, so it is good to use a high nitrogen fertilizer when plants are in their active growth phase. For example, citrus trees respond well to nitrogen when you give it to them in spring and summer. However, if you give a plant too much nitrogen later in the year, it can send out tender new foliage that might be in danger of frost damage when fall brings the first frost. Many animal manures are high in nitrogen, so you must use caution when using fresh manure because it can burn tender plants. If you want to stimulate fruit or flower production, choose a low nitrogen or "bloom booster" fertilizer. Although it's a good idea to give plants, such as tomatoes, plenty of nitrogen when they are first growing, if you want to increase your harvest later in the summer, stop fertilizing with nitrogen when flowers start to form.

Effects of Too Much Fertilizer

Plants that receive more fertilizer than they need also need additional water, according to Washington State University. An excess of nitrogen that is contained in most fertilizers causes tender new vegetative growth that can attract insect pests, such as aphids. Plant diseases, such as powdery mildew, can easily find a good growing ground on succulent new growth that results when a plant receives an excessive amount of nitrogen. When large quantities of nitrogen and phosphorus are used on crops in large-scale farming, it can easily run off into ground water and bodies of water in the area, such as rivers and lakes. This can cause water pollution that results in algae growth, according to Washington State University.

Keywords: plant food, fertilizer nutrients, chemical organic fertilizer

About this Author

Barbara Fahs lives on Hawaii island, where she has created Hi'iaka's Healing Herb Garden. Fahs wrote "Super Simple Guide to Creating Hawaiian Gardens," and has been a professional writer since 1984. She contributes to Big Island Weekly, Ke Ola magazine, GardenGuides and eHow. She earned her B.A. at UCSB and her M.A. from San Jose State University.