Understanding fertilizers

Sorting through fertilizers presents a bit of a challenge. It's easy to be overwhelmed by the product choices that await you at any garden or home improvement centre. Yet, as these tips will show, choosing and using fertilizers need not be complicated.

Understanding fertilizers

The basics

Depending on the type of garden you have, you will probably need only a few products to meet the nutritional needs of all of your plants.

Every box or bag of fertilizer lists three numbers on the label, which represent how much of the three primary plant nutrients — in order: nitrogen, phosphorus, potassium — are contained in the bag, box or bottle.

  • Nitrogen contributes primarily to the development of healthy green leaves and stems.
  • Phosphorus contributes to the growth of roots, flowers and fruit.
  • Potassium also aids in flower and fruit production, but in addition, it promotes plant health and resistance to disease and environmental stress.

When one or more numbers in a fertilizer analysis are higher than the others, it indicates that there is more of one nutrient, as in 14-4-4, which is a formulation that is high in nitrogen. If you relate this to the description of nitrogen, above, you can see that this formulation would be a good one to use on a green lawn or to fertilize leafy, green garden plants. High numbers, such as 20-20-20, simply show that a fertilizer product is very concentrated and will require dilution before being applied, whereas low numbers, such as 4-4-4, indicate lesser amounts of the same nutrients and less dilution is needed.

You do not have to be a mathematician to figure out how much of any fertilizer to use; simply follow the application rates given on the package label. Because they are so concentrated, manufactured fertilizers usually have high numbers, so you will use a relatively small amount of them with each application.

Organic fertilizers, made from manure, alfalfa meal, feather meal or many other natural ingredients, have comparatively low numbers, so more is required to accomplish the same fertilization as the manufactured ones. Not surprisingly, potent manufactured fertilizers usually cost more per pound than their bulkier organic counterparts. And manufactured fertilizers, unless they are slow-release formulas, usually work faster than organic ones, which release their nutrients slowly over several months. In most cases, it is advantageous to apply fertilizers that release nutrients slowly enough for plants to absorb them, to reduce runoff and waste.

Timed-release fertilizer

  • They cost a little more than regular granular fertilizers, but dry fertilizers in which some of the granules are coated to slow down the release of nutrients to plants are an excellent value.
  • When used according to label directions, they can fertilize plants for up to nine months with a single application.

These basic guidelines will help you choose the right fertilizer for your lawn.

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