What Time of the Year to Fertilize Grapevines?

Foliar Fertilizer Sprays

• Some fertilizers are available as foliar sprays, which growers apply to the leaves of grapevines rather than the soil. Zinc foliar sprays work best when applied between three weeks prior to bloom and up to the period of blooming, according to the University of California Davis. Magnesium foliar sprays are useful throughout the season if the grapevine's health indicates a deficiency of this nutrient. Foliar sprays of magnesium work well when applied with soil-based magnesium.

Nitrogen Fertilizers

• Nitrogen is an essential nutrient for grapevines. A deficiency of nitrogen in the soil leads to weak growth, while excess nitrogen or nitrogen applied at the end of the growing season leads to unnecessary growth and growth that is more likely to be damaged. According to the University of Kentucky, nitrogen works best when applied around the time of fruit set on the grapevines. This supplies the grapevines with nutrients for continued maturation of grapes.

Potassium

• Potassium deficiency is associated with discolored, weak leaves and poor overall growth. Soils with a high clay content are more likely to lack potassium. Foliar sprays of potassium supply the grapevine with a temporary boost, but soil treatments are more effective and long-lasting. Apply a potassium fertilizer or potash to the soil when the grapevine starts showing signs of deficiency, such as browning of the leaves. Symptoms of deficiency appear on younger grapevine leaves first.

General Fertilizer Guidelines

• Many fertilizers contain nitrogen, phosphorus and potassium, as well as micronutrients like iron, zinc and magnesium. General plant food fertilizers work well as boosters for grapevines in the early spring. Apply fertilizers a week after grapevines are initially planted, and in the early spring before the grapevine produces new growth each year after. According to the Ohio State University, grapevines are unable to produce a full harvest until they are 4 or 5 years old.