How Does Plant Fertilizer Work?

Chemicals In Fertilizer

Plants require three main nutrients in order to remain in good health: nitrogen, phosphorous and potassium. Each element provides a certain component that satisfies a specific need for healthy plant growth. Fertilization ensures that enough of each element is present in the soil for the roots to feed on. Even soil already rich in one of these elements may not naturally replenish it quickly enough for a growing and feeding plant. Commercial fertilizers combine these three chemicals in specific amounts depending on the needs of the plant variety. Fertilizers provide other elements including calcium, magnesium, iron and zinc, but these are not as important to most plants as the primary three.

Nitrogen

Nitrogen encourages lush foliage growth. Leafy plants including grasses, trees and lettuces need more nitrogen than flower- and vegetable-producing plants as they produce more foliage. Apply nitrogen early in the development of most plants, usually in spring, to encourage healthy foliage growth. A second high-nitrogen fertilization in midsummer replaces the nitrogen in the soil the plants have consumed so they will continue leaf production through autumn when the leaves usually drop, die off or go dormant for winter.

Phosphorous

Vegetables, fruit and flowering plants benefit the greatest from phosphorous-rich fertilizers. Phosphorous feeds encourage seed production. Flower production is how the seeds are formed, either as an ornamental flower or a flower that will later develop seeds within an edible fruit or vegetable. Add phosphorous fertilizers right as buds begin to form on the plants in spring and again in the summer for plants that bloom all season long.

Potassium

Potassium aids disease resistance in plants as well as encouraging vigor. It is especially beneficial for fruiting trees and bushes as fruit production places a stress on the plants, making them more prone to disease and potassium starvation. Supplement plants with a potassium-rich feed at the onset of fruiting or when buds begin or in late spring for nonfruiting plants.

Types of Fertilizer

Fertilizers come in several varieties including liquid, granules and slow-release. Liquid fertilizer quickly permeates the soil where the roots absorb it. Liquid fertilizers must be applied more often than other types but benefit container plants as other types of fertilizer leach out of the containers before the plants have a chance to absorb them. Slow-release fertilizers usually come in granule form. These release slowly over time so the plant reaps the benefits of the feed for several weeks or months.

Reading Fertilizer Labels

Fertilizers come in varieties formulated for vegetables, roses and other plant varieties. Most important is the three numbers listed on the bag, such as 10-10-10. The first number is the percentage of nitrogen in the mix, the second is phosphorous and the third is the potassium amount. Leafy plants require the first number to be higher than the other two, while flowers do best if the second number is the greater of the three.