When and How Often to Apply Plant Food: Tips, Timing, More In the Mailbag from Dan Gill | Home & Garden


QUESTION: I’m trying to decide when to fertilize the many types of plants in my landscape. I don’t know when to start fertilizing or when to stop. What is the best fertilizer to use and how often should it be applied? – Sam Du Pont

REPLY: You’re not alone. I get these questions all the time. First of all, keep in mind that nothing will die in your landscape if you don’t fertilize. Fertilization is not done to keep the plants alive, but to make sure they grow at their best. You don’t need a rigid schedule that needs to be followed precisely. It’s not that hard.

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Generally speaking, the best time to fertilize landscape plants is around the time they begin to actively grow. The worst time to fertilize plants is at the end of their growing season. Trees, for example, begin to wake up and grow in early spring and are usually fertilized once in February or March. Most shrubs are actively growing in spring and early summer, so we tend to fertilize them once around March or April. Lawns are allowed to green before being fertilized in late March or early April and are fertilized again in mid-summer.

Flower beds and vegetable gardens are usually fertilized just before planting. Particularly important is the fertilization of flowers and vegetables. We want maximum performance from these plants, and fertilizers help to achieve that.

Not everything starts to grow in the spring. Louisiana irises, for example, are at the end of their growing season in the spring and are dormant during the summer. They start to grow in October, and now is the time to fertilize them. Trees and shrubs, on the other hand, go dormant in the fall and should not be fertilized.

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You don’t need separate fertilizers for all of this, and there is no better fertilizer. For landscape fertilization, choose a general purpose granular fertilizer that has an analysis with a higher first number, the lower number in the middle, and a third number in between, such as 15-5-10. The exact numbers are not critical.

You also wonder how often to fertilize, and it depends on what you use. The fertilizer label will tell you the rate (amount) of fertilizer to apply and how often it should be used. Soluble fertilizers, for example, are applied every two weeks during the growing season. Granular fertilizers are typically applied about every six to eight weeks. Slow-release fertilizers work for months, so a single application is usually all that is needed for a growing season.

Dan Gill is a horticulturalist at LSU AgCente.r Have a gardening question? Email Dan Gill at dgill@agcenter.lsu.edu


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