As we approach bloom, now is the time to think about fertilization in your vineyard. Nitrogen, in particular, should be available by bloom to support strong canopy growth and fruit set. The best way to guide fertilization is by reviewing last year’s petiole nutrient analysis, but there are additional indicators that can help determine whether adjustments are needed this season.

Use Multiple Indicators to Guide Fertilization

In addition to petiole analysis, early-season shoot growth is a useful visual cue. For most wine grape cultivars, normal shoot length ranges from 3 to 7 feet. Well-balanced vines typically produce shoots of 3 to 6 feet, which support 12–15 mature leaves per cluster.

If shoots are noticeably shorter or show signs of nutrient deficiency—such as pale foliage, weak growth, or uneven development—it may signal a need to adjust your nitrogen management program.

Nitrogen Fertilization Recommendations for Bearing Vineyards

Based on mid-summer petiole N concentrations (July–August), follow these nitrogen fertilizer guidelines:

Petiole N (%)	N Fertilizer to Apply (lb N/acre)
> 1.5	0
1.3 – 1.5	20
0.9 – 1.3	30
< 0.9	40–50

• Each ton of grapes removes approximately 3.6 lb of nitrogen per acre. For example, a 4-ton/acre crop removes about 14.5 lb N/acre.
• Nitrogen should be applied in early spring, so it is available by bloom.

Choosing the Right Nitrogen Source

When selecting a nitrogen fertilizer, it’s important to understand how different forms behave in the soil:

• Nitrates (e.g., Calcium Nitrate, Potassium Nitrate):
  Fast-acting and immediately available to vines, but prone to leaching—especially in sandy soils or with heavy rain.
• Urea (CO(NH₂)₂):
  Common and affordable, but volatile under warm conditions if surface-applied without incorporation.
• Ammonium forms (e.g., Ammonium Nitrate):
  Slowly available—must convert to nitrate (NO₃⁻) in the soil before uptake. This conversion requires soil temperatures above 50°F, but ammonium is less prone to leaching than nitrate.
• Manure-based nitrogen (NH₄⁺):
  Best applied after harvest in the fall, once vine growth has ceased, to avoid stimulating late-season growth.

By integrating petiole analysis with shoot observations and choosing the appropriate fertilizer type, you can support balanced vine growth and fruit quality throughout the season.

This article was posted in Grapes and tagged Amaya Atucha, Fertilizing Wine Grapes, Grapes, Petiole Nitrogen, Shoot Growth, wine grapes.