AMES, Iowa – Planting small fruits in gardens is a popular part of spring. But some need more support than others. When is it right to fertilize small fruits? Or should it be done at all?
Iowa State University Extension and Outreach horticulturists can help answer questions about how to best handle small fruits in spring. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or firstname.lastname@example.org.
Established plantings of June-bearing strawberries should not be fertilized in spring. Spring fertilization stimulates foliar growth, produces softer berries and increases disease problems. Lush, vegetative growth may make picking difficult. Also, soft berries are more likely to be attacked by fruit rots. As a result, a spring fertilizer application may reduce the fruit yield.
Fertilizer should be applied to June-bearing strawberries during the renovation process immediately after the last harvest of the season. Apply approximately 5 pounds of 10-10-10 or a similar analysis fertilizer per 100 feet of row.
Everbearing and day-neutral strawberries can be fertilized in early spring and again in early August. Apply 5 pounds of 10-10-10 or a similar analysis fertilizer per 100 feet of row.
Fertilize established raspberries in early spring before new growth begins. Apply 4 to 5 pounds of 10-10-10 or a similar analysis fertilizer per 100-foot row. Uniformly broadcast the fertilizer in a 2-foot band. If the raspberries are mulched with sawdust or wood chips, apply a slightly heavier rate (5 to 6 pounds of 10-10-10 per 100-foot row) of fertilizer. Conduct a soil test every four or five years to determine if nutrient levels are adequate.
Do not fertilize raspberries in late spring or summer. Late spring or summer fertilization encourages succulent, late season growth. Late season growth is susceptible to winter damage.
Fertilization is generally not necessary for grapes in Iowa. Iowa's fertile soils contain adequate supplies of essential plant nutrients. Excessive fertilization is harmful. Too much nitrogen may promote rampant vegetative growth and delay vine and fruit maturity. Fertilize grapevines only when plants exhibit weak growth or poor leaf color.
When poor growth dictates fertilization, apply a complete, low analysis fertilizer, such as 10-10-10, in early spring. Do not fertilize grapevines in late spring or summer. Late spring or summer fertilization encourages succulent, late season growth, which is more susceptible to winter damage.
Established blueberry plants benefit from an annual application of an acid-producing fertilizer, such as ammonium sulfate. In early spring, apply ½ to 1 pound of ammonium sulfate per 100 square feet of garden area. Ammonium sulfate supplies nitrogen to the plants and also helps to maintain soil acidity.
Established gooseberries and currants can be fertilized in spring. Apply 8 ounces of 10-10-10 or a similar analysis fertilizer in a band around each plant.