Feeding plants doesn’t need to be treated as an exact science. The soil they are growing in supplies most of their nutrients. The gardener’s job is to keep the reservoir of nutrients replenished. In general, clay soils hold the most nutrients and sandy soils the least. Container soils need frequent replenishment.
Soils that get lots of summer rain are often acid and low in nutrients. You are likely to need to add complete fertilizers. Soils that get little rainfall, or that get their rain during the winter, are often alkaline and rich in mineral nutrients. In these soils, nitrogen may be the only nutrient you need to add on a regular basis, but complete fertilizers do no harm.
Soil tests for plant nutrients are excellent tools for farmers, but of less value for home gardeners. It’s helpful to have the soil tested once to learn the phosphorus and potassium levels, but after that, it’s simpler to add fertilizer than to test on a regular basis. The cost of a little too much fertilizer doesn’t make the difference to a home gardener that it does to a farmer, and moderate amounts of extra nutrients do no harm to plants.
Because nitrogen is the fertilizer most frequently needed, a simple way to fertilize is to add complete fertilizer when the plants need nitrogen and ignore the other nutrients. They will be taken care of with the complete fertilizer.
Trees and shrubs need less fertilizer than flowers or vegetables. One feeding in the spring, about the time plants are leafing out, is usually sufficient for them. Because their roots spread so far, they are getting benefit from other feedings you make through the year, also.
Broadcast a complete fertilizer over the whole garden, or at least the tree and shrub areas at a rate of about 1 pound of actual nitrogen per 1,000 square feet. That’s 10 pounds of 10–10–5 or 20 pounds of 5–10–5 per 1,000 square feet.
Different plants require different levels of fertilizing. Since home gardeners usually grow a variety of plants, they need to know the relative fertilizer needs of the plant. Generally speaking, the following plant groups have high, medium, or low needs for the primary nutrients of nitrogen, phosphorus, and potassium.
|Lawns||Medium to high|
|Perennial flowers||Medium to low|
|Deciduous trees and shrubs||Medium to low|
|Herbs||Low to medium|
|Evergreen trees and shrubs||Low|