Commercial fertilizers and manures are applied to supplement a soil's natural fertility. The rate of material to apply varies according to past fertilizer use, crop grown, soil type, and other factors. The following are general fertilizer recommendations for established tree and small fruits in the home garden.
June-bearing Strawberries -- Established plantings of June-bearing strawberries should not be fertilized in spring. Spring fertilization stimulates foliar growth, increases disease problems, and produces softer fruit. Lush, vegetative growth may make picking difficult. Also, soft fruit are more likely to be attacked by fruit rots. As a result, spring fertilization may actually reduce the fruit yield. June-bearing strawberries should be fertilized during the renovation process immediately after the last harvest of the season. Apply approximately 5 pounds of a 10-10-10 or similar analysis fertilizer (such as 12-12-12) per 100 feet of row.
Everbearing and Day-neutral Strawberries -- Apply 5 pounds of a 10-10-10 fertilizer per 100 square feet to everbearing and day-neutral strawberries in early spring and again in early August.
Raspberries -- Established raspberries should be fertilized in spring before new growth begins. Apply 4 to 5 pounds of a 10-10-10 or similar analysis fertilizer for each 100 feet of row. Uniformly broadcast the fertilizer in a 2-foot band. If the raspberries are mulched with sawdust or wood chips, apply 5 to 6 pounds of 10-10-10 per 100 feet of row. Do not fertilize raspberries in late spring or summer. Late spring or summer fertilization encourages succulent, late season growth which is susceptible to winter damage.
Manure may be used as an alternative to commercial fertilizers. Apply 50 to 100 pounds of well-rotted barnyard manure (cow, hog, or horse) per 100 feet of row.
Currants and Gooseberries -- Apply about 1 cup of a complete fertilizer, such as 10-10-10, in a circular band around each plant in early spring. Manure is another option. Apply 1/2 to 1 bushel of well-rotted manure uniformly around each plant in late fall or early spring.
Grapes -- It is generally not necessary for home gardeners to fertilize grapes in Iowa. Fertilize grapevines only when plants exhibit weak growth or poor leaf color. Use a complete fertilizer, such as 10-10-10. Broadcast 1/2 pound around each plant. Too much nitrogen may promote excessive vegetative growth and delay vine and fruit maturity. The best time to fertilize is early spring. Do not fertilize grapevines in late spring or summer.
Blueberries -- Once established, apply 1/2 to 1 pound of ammonium sulfate per 100 square feet of garden area. Apply the material in broad bands around plants in early spring before budbreak. Do not fertilize after the bloom period. Ammonium sulfate supplies nitrogen to the plants and also helps to maintain soil acidity.
Fruit Trees -- It is generally not necessary to fertilize fruit trees. Check tree growth to determine whether fruit trees need fertilization. Nonbearing fruit trees should grow approximately 15 to 30 inches per year. Bearing trees should produce 8 to 15 inches of new growth. (The actual amount of new growth will vary due to differences in varietal vigor.) Fruit trees making less than desirable growth may need fertilization. Apply a balanced fertilizer, such as a 10-10-10, in early spring before bud break. The recommended rate is 1/10 pound of actual nitrogen per year of tree age. (Tree age is the number of years since the tree was planted in the home garden.)
For example, a 5-year-old tree should receive 5/10 or 1/2 pound of nitrogen. Uniformly broadcast 5 pounds of the 10-10-10 fertilizer (10 percent of 5 is 1/2 pound of N) in a circular band beginning about 2 to 3 feet from the trunk and extending out slightly beyond the dripline of the tree. One pound of actual nitrogen is the maximum for fruit trees 10 years of age and older.
If the lawn in the vicinity of the fruit trees is fertilized on a regular basis, there should be no need to fertilize the trees. The fruit tree roots will absorb nutrients from the lawn fertilizer. Additional fertilizer may be excessive.
When fertilizing fruit trees, the timing of the application and amounts are crucial. Early spring is the best time to fertilize fruit trees. Avoid fertilizing in late spring or summer as this may stimulate late summer growth that is more susceptible to winter injury. Too much fertilizer produces excessive vegetative growth and inhibits fruiting.