The regular use of fertilizers in landscape plants including turf, trees and shrubs is an important maintenance practice. Soils are often deficient in nutrients required for optimal plant growth and these need to be supplemented in the form of fertilizers. Fertilizers are primarily sold in the liquid and dry forms and the shelf life of both differs. Shelf life indicates the maximum time for which fertilizers may be stored without losing strength.
Dry fertilizers come in granular form and are most commonly used for fertilizing large shrubs, trees and lawns. These fertilizers do not lose strength when they are stored for long periods of time. As cited by the Scotts Miracle-Gro Company, fertilizers in the dry form have an indefinite shelf life.
Liquid fertilizers come in a liquid form and are either applied to the soil for root absorption or are sprayed on the plants for foliar absorption. Unlike dry fertilizers, liquid fertilizers do not retain their strength when stored for more than a certain period of time. The maximum period of time for which liquid fertilizers are expected to stay good is from eight to 10 years, cites the Outside Pride company.
Fertilizers often contain herbicides or pesticides targeted to control weed and pests. These products are referred to as weed-and-feed and help the user attain two goals in a single application. Fertilizers that contain chemicals have a shorter shelf life and lose their strength after a certain period of time. The Washington State University Extension website lists two to four years as the maximum time at which chemicals retain potency. Hence dry or liquid fertilizers containing chemicals are only viable for two to four years.
The requirement for fertilizer is most frequently indicated by the growth condition of plants. Plants that are growing in nutrient-deficient soil start to display physical symptoms such as chlorosis or light green to yellow leaf color. There is premature leaf drop with earlier fall colors in deciduous plants. The branch and twig growth of plants is stunted and reduced and the plant loses vigor overall.