April 19, 2018

Petiole Analysis as a Guide to Grape Vineyard Fertilization

Carl Rosen, Professor, Department of Soil, Water and Climate

Revised 8/28/2008

Principles of Tissue Analysis: The basis behind tissue analysis is that optimum ranges exist for the level of each nutrient in plant tissue and maximum quality/yields occur when nutrients are maintained within these ranges. If the level of a nutrient falls outside of its optimum range, corrective measures should be taken.

Many factors affect the nutrient composition of plant tissue. Soil moisture, soil texture/structure, native soil fertility, and fertilizer practices have direct effects on nutrient uptake. Crop load, variety, rootstock, disease and insect incidence, weather conditions, and cultural practices such as weed control and pruning can also alter tissue nutrient composition. Whenever possible, consideration of these factors should be taken into account when interpreting tissue analysis results. Fertilizer application is often necessary to provide optimum levels and balance of nutrients for plant growth, but fertilizer cannot make up for poor insect and disease control or correct problems like severe damage due to winter injury.

Petioles (stem portion of the leaf, see Fig. 1) are the tissue recommended for determining the nutritional status of grapevines. In most other fruit crops, the entire leaf is used, but research has shown that petiole tissue is best for grapes. When used properly, petiole analysis provides the most reliable method to determine fertilizer needs for established vineyards. Soil tests should be used prior to planting to determine organic matter and pH levels, lime requirements, as well as phosphorus, potassium, magnesium and micronutrient needs. In established vineyards, however, soil tests are primarily used as a supplement to tissue analysis information. The table below provides the nutrient sufficiency levels established for grape petioles from established vines.

Recommended Procedures for Sampling and Handling Grape Petioles: Obtaining a representative sample is important to avoid misleading results and erroneous interpretations. Even the best-equipped laboratory cannot make up for a poorly collected or improperly handled sample. Optimum nutrient ranges are based on petioles sampled at a specific maturity level and collected at a specific period during the growing season. The following guidelines should be used for proper sampling and handling procedures:

  1. For grapes, there are two times of the season recommended for testing – full bloom (mid to late June) and early veraison (mid July to mid August). While both sampling periods have established sufficiency levels, the mid-July to mid August timing is generally thought to provide a more accurate assessment of grapevine nutrient status.
  2. At least 25 to 50 vines should be selected for sample collection. Vines not typical of the vineyard should be avoided.
  3. Vines should be of the same age, variety, and rootstock, growing on a relatively uniform soil of the same fertility. If these conditions are not met, divide the vineyard into uniform blocks and sample separately.
  4. For full bloom time sampling, take the petioles from leaves opposite the bottom flower cluster (Fig. 2). For samples collected in mid July to mid August, take petioles from the most recently developed matured leaf (Fig 3).
  5. Collect a total of 75 to 100 petioles (more may be required from cultivars with short petioles) from 2 or 3 leaves on the vine. Do not pick more than 1 leaf from any one shoot. Discard the blade and keep the petiole. Leaves showing insect, disease, or mechanical damage should not be selected for sampling.
  6. If you are trying to diagnose specific symptoms, send in two samples – one set of 75-100 petioles from vines showing the symptoms and another set from vines not showing symptoms. This can be done at any time of the growing season.
  7. If petioles are dusty or dirty, they can be rinsed in distilled or deionized water. Do not let petioles soak in water, because nutrients will leach out. Dried petioles should not be washed.
  8. Place petioles in a clean paper bag and dry at room temperature or send immediately to a laboratory. Do not use plastic bags unless samples have been previously dried.

The University of Minnesota Research Analytical Laboratory  offers tissue testing services for a fee. 

A number of other laboratories also offer tissue testing services. More information about other laboratories located in the Upper Midwest can be found in the following Minnesota Department of Agriculture.

Figure 1. Grape leaf showing blade and petiole. Keep the petiole for analysis and discard the blade.

grape leaf and petiole

Figure 2. Select petioles from leaves opposite basal cluster at full bloom.

leaf and cluster

Figure 3. Select petioles from the most recently developed mature leaf in mid July to mid August.

select petioles

Nutrient sufficiency levels in grape petioles sampled at full bloom (mid to late June) and at early veraison (mid July to mid August)


Full Bloom

(mid to late June)

Early Veraison

(mid July to mid August)

Nitrogen (%)
No data (>0.10)
No data (>0.10)

Note: If pesticides containing copper, zinc, or manganese were sprayed on the vines, then concentrations of these elements may be much higher in the tissue. This is usually not a cause for concern, because most of the sprayed elements are on the tissue surface.

Soil Test Interpretations for Grape Vineyards

Soil testing for grapes is strongly recommended for before the vineyard is established. Once established it is very difficult alter pH and levels of many nutrients because incorporation more than a couple of inches is not possible. For initial sampling, two depths, 0-10” and 10-20” are recommended; however, interpretations and recommendations are based primarily on the surface 0-10” sample. Samples can be collected any time of the year, although spring and fall are usually the most convenient. Each field to be sampled should be divided into uniform areas. Each area should have the same soil texture and color, cropping history, and fertilizer, manure and lime treatments. One sample should not represent more than 20 acres on uniform land and 5 acres on rolling land. Samples are most easily collected using a soil sampling tube, soil auger, or garden spade. Usually 15 to 20 subsamples (one core per subsample) should be collected from randomly selected areas in the field. The subsamples should be thoroughly mixed in a plastic pail and about 1 pint placed in a sample bag or box. Visit the U of M Research Analytical Lab for submission forms.

Information about other soil testing labs can be obtained from the Minnesota Department of Agriculture.

Organic matter (combustion):

less than 3.1%- low

3.1 to 4.5% – medium

4.6 to 19% – high

more than 19% – peat or muck

pH (1:1, soil:water):

less than 7 – acid

7 – neutral

greater than 7 – alkaline

6 to 7 – optimum except for acid loving plants

Phosphorus (Bray P1) – on soils with pH 7.4 or less:

0 to 5 ppm – low

6 to 10 ppm – medium

11 to 15 ppm – medium-high

16 to 25 ppm – high

more than 25 ppm very high

Phosphorus (Olsen P) – on soils with pH > 7.4:

0 to 3 ppm – low

4 to 7 ppm – medium

8 to 11 ppm – medium-high

12 to 18 ppm – high

more than 18 ppm – very high

Potassium (ammonium acetate extractable):

0 to 50 ppm – low

51 to 100 ppm – medium

101 to 150 ppm – high

more than 150 ppm – very high

Magnesium (ammonium acetate extractable):

0 to 50 ppm – low

51 to 100 ppm – medium

more than 100 ppm – high


Calcium (ammonium acetate extractable):

0 to 300 ppm – low

301 to 600 ppm – medium

more than 600 ppm – high

Boron (hot water extractable):

0 to 0.5 ppm – low

0.6 to 1.0 ppm – medium

more than 1 ppm – high

Zinc (DTPA extractable):

0 to 0.5 ppm – low

0.6 to 1.0 ppm – medium

more than 1 ppm – high

Manganese (DTPA extractable):

 0 to 1 ppm – low

1.1 to 5.0 ppm – medium

more than 6 ppm – high

Copper (DTPA extractable):

0 to 0.1 ppm – low

0.1 to 0.2 ppm – medium

more than 0.2 ppm – high