Succulent red fruits, deep green foliage and delicate white flowers make strawberries (Fragaria spp.) both useful and ornamental. Strawberries thrive in U.S. Department of Agriculture plant hardiness zones 3 through 9. Access to the proper nutrients in the soil helps ensure your strawberries produce well and look their best. Timing fertilizer applications correctly and using the right fertilizer types result in the healthiest plants.
The best guide for fertilizer needs and amounts is a soil test. Although home soil testing kits are available, these may not provide a sufficient nutrient analysis for determining the fertilizer needs in the strawberry beds. When possible, take a soil sample to a testing laboratory to determine fertilizer needs. It's best to test the soil at least six months before planting the strawberries, then again at one- to two-year intervals. If a soil test isn't performed, it's still possible to fertilize the strawberries by following general fertilizer guidelines.
Fertilization and soil improvement begins before you plant the strawberries. Compost or well-aged manure adds nutrients and improves the soil and quality of the site. You can add compost up to six months before planting, or in fall for spring-planted strawberries. A 2- to 3-inch layer worked into the soil to a 6-inch depth works well. Immediately before planting, apply fertilizer following the soil test recommendations or work in a general application of 1 pound of 6-24-24 fertilizer into every 50 square feet of garden. Mix the fertilizer into the top 6 inches of soil.
Annual fertilizers are usually applied in late summer or fall, after you've harvested the berries but before you prune back the plants each year. In lieu of a soil test, a balanced general-purpose fertilizer, such as a 10-10-10 or 12-12-12, usually suffices. Apply about 1 pound of the fertilizer per 50 foot row the first year, and up to 2 pounds of the fertilizer each following year. Avoid placing the fertilizer directly on the plants. Instead, spread it down the row about 6 inches from the base of the strawberries and water thoroughly after application so the fertilizer can soak into the soil.
Although strawberries can grow without sidedressing, a midseason fertilizer application can result in healthier plants and better fruiting. Nitrogen fertilizers are the most beneficial, and result in deep green healthy foliage, but you can also use a general-purpose 12-12-12 fertilizer. Apply the sidedressing about four weeks after the plants resume active growth in spring or early summer, then sidedress again about four weeks later. Use 3/4 pounds of ammonium nitrate fertilizer per 50 foot row, or substitute 1 pound of 12-12-12 fertilizer. Alternatively, follow soil test recommendations.