Gardening Articles: Landscaping :: Trees, Shrubs, & Vines
Controlled-Release Fertilizers (page 3 of 3)
by Warren Davenport
Comparing Fertilizer Costs
The best way to compare costs of fertilizers is to calculate the cost per pound of its nitrogen. Multiply the weight of the material by the percentage of nitrogen (as a decimal), then divide that number into the price. For example, the nitrogen in a $3.97, 1-1/4-pound package of 14-14-14 costs $22.69 per pound: $3.97 divided by (1.25 x .14).
How to Use
The key benefits of slow- and controlled-release fertilizers are their ease of use, reduced number of applications, and more specific and accurate directions on the product label. However, if you have never used them before, you might have general questions. Here are guidelines for some common situations.
Houseplants. Actual nutrient needs depend upon the particular plant and how fast it's growing. Especially in fall through spring, when growth slows and water needs decrease, use at half the recommended rate. However, if growth is fast, as in a sunroom or under artificial lights, or if new leaves are pale yellow, increase the rate.
Outdoor container plants. Fertilize most outdoor container plants at the recommended rate. Start just before spring growth starts, and choose a fertilizer according to how long your plants will remain in the pots (which may be the same as the length of your season). In most areas, make one application of an eight- to nine-month formulation, or two of a three- to four-month one.
Lawns. Most quality brands of lawn fertilizer contain a significant proportion of controlled- release nitrogen. The most commonly used sources are SCU, methylene urea, or polymer-coated urea.
Lawn-fertilizing schedules abound. Generally it is best to fertilize lawns just prior to periods of active growth. That means spring and fall for cool-season, northern grasses; spring and summer for warm-season southern grasses.
Most northern lawns need about 2 to 3 pounds of "actual" nitrogen for every 1,000 square feet each season to remain healthy; southern lawns of Bermuda grass need twice that. Calculate the needed amount of fertilizer by dividing the pounds of actual nitrogen you want to apply by the percent (as a decimal) of the nitrogen in your fertilizer. For example, 11 pounds of an 18 percent nitrogen fertilizer equals 2 pounds of actual nitrogen.
Check with your local cooperative extension agent for specifics, and follow label recommendations.
Landscape plants. If your plants are closely grouped and the roots overlap, scatter 10 to 15 pounds of a three- to four-month 14-14-14 controlled-release fertilizer over 1,000 square feet. The best time is late winter or early spring. Repeat again in late fall. If applied only once a year, spread 17 to 22 pounds of 18-6-12 over the same area.
Flowers. For indoor flowers, follow the directions for houseplants. For annuals or perennials, apply as directed for landscape plants. Apply at planting time or shortly after. Incorporate the fertilizer into the top 2 to 3 inches of soil, or scatter it evenly over the soil surface. Don't pile it on or near the plant's base.
Vegetables. Fast-maturing cool-weather vegetables such as radishes and lettuce are best fertilized with a fast-release fertilizer, because the soils are too cool to allow nutrient release from most slow-release, controlled-release, or organic fertilizers. For warm-season crops such as tomatoes and corn, use a three- to four-month 14-14-14 controlled-release fertilizer at planting time. Incorporate at a rate of about 10 pounds over 500 square feet of soil.
Warren Davenport is president of PAT2H Consulting Services, a horticultural research company in Rydal, Georgia.
Photography by John Goodman