LSU AgCenter's Weekly Message

Fertilizing Landscape Beds

Sometimes landscape beds are installed and, perhaps, mulch is refreshed and pruning is performed from time to time, but little attention is given to replacing nutrients that have leached out of the soil with rain or irrigation water or that have been removed in pruning waste. Over time, plants become less vigorous.

Late winter and early spring, as the aboveground parts of plants start growing again, are good times to fertilize many plants. This includes shrubs, small trees, and herbaceous perennials in landscape beds.

Taking a soil test and getting the results is preferable for knowing what amounts of different nutrients are needed and if soil pH needs to be adjusted. However, if there is no reason to believe that soil nutrient levels might be excessive, an application of a “complete” fertilizer – one containing nitrogen, phosphorus, and potassium – can be made at a moderate rate without one.

Fertilizing at a rate of 1 pound of actual nitrogen per 1000 square feet, or 0.1 pound per 100 square feet, is a rule of thumb when maintaining landscape ornamentals. If you’re using a slow-release fertilizer, you might consider increasing the nitrogen rate to 0.2 pound per 100 square feet. (Slow-release fertilizers are coated in such a way that nutrients are released over time and, for landscape beds, are preferred to ones like 13-13-13 or 8-8-8 that are readily soluble.)

For example, you could use 0.7 to 1.4 pounds of a slow-release 15-9-12 (15% nitrogen) product, 0.8 to 1.6 pounds of a slow-release 12-6-6 product (12% nitrogen), 0.8 pound 13-13-13 (13% nitrogen), or 1.3 pound 8-8-8 (8% nitrogen), per 100 square feet of bed area. These are just a few of many possible fertilizers that could be used.

Mixed fertilizers generally have a density of about 1 pound per pint, or per 2 cups, so 0.5 pound of fertilizer would be about 1 cup of fertilizer.

While landscape beds can be fertilized in late winter or early spring, wait until April to apply any nitrogen-containing fertilizer to warm-season turfgrasses. Fertilizing turfgrass too early can promote winter weed growth and predispose grass to the fungal disease large patch.

Let me know if you have questions.

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Dr. Mary Helen Ferguson is an Extension Agent with the LSU AgCenter, with horticulture responsibilities in Washington and Tangipahoa Parishes. Contact Mary Helen at mhferguson@agcenter.lsu.edu or 985-277-1850 (Hammond) or 985-839-7855 (Franklinton).