Managing and understanding grapevine nutrition can be a daunting task. Mineral nutrients are important to the entire vine as they play vital roles in plant biochemistry. An effective vineyard fertility program is developed from site-based information, including records of fertilizer and irrigation inputs, plant growth assessments, yield data, and plant tissue and soil test results.

Soil testing alone is not useful in predicting vine nutrient status due to a variety of issues, such as:

  • Differences in nutrient uptake or requirements of different varieties, clones, and rootstocks;
  • Differing irrigation and soil management practices; and
  • The plasticity of vine roots to explore soils in different environments.

In addition, grapevines can store significant quantities of some nutrients to overcome short-term deficits of soil supply, and this ability increases with vine age. For example, more than 50% of the canopy nitrogen (N) and phosphorus (P) came from stored reserves in the roots and trunks of nonirrigated mature ‘Pinot noir’ vines studied in Oregon.

Soil analysis is useful in monitoring changes over multiple years, including pH and soil organic matter that can impact nutrient supply in the soil. Soil analysis is most useful in determining potential vineyard planting sites. However, once a vineyard is planted, yearly soil tests are not necessary.

Plant tissue testing is a better measure of vine nutritional health. Many wine grape growers collect petiole samples from their vineyards every year or two and send them to a testing lab for analysis. The lab results often end up in a desk drawer unless something appears alarming. Nutrient testing can be more useful if consistent, representative samples are collected each year. It is also important to understand and correctly interpret tissue analysis data.

What do grapevine tissue test results tell you?

The data you receive in a plant tissue analysis report is the nutrient concentration; it is the amount of each nutrient per amount of petiole or leaf blade mass. Many assume that nutrient concentrations equal nutrient uptake. However, this is not always true. The only way to be sure about nutrient uptake is to monitor the content of nutrients that equates to the concentration of the nutrient in the whole vine multiplied by total vine mass that accounts for growth differences. Rapid growth of healthy vines can dilute the concentration of nutrients in leaves and petioles.

Tissue tests results are more meaningful if you also have some measure of plant growth near the time of sample collection. This can be as simple as a rough estimate of how close shoots are to the top wire at bloom or how full the canopy is at véraison. Results from tissue analysis are most useful when combined with other information from your site, such as:

  • Previous and current season’s growth (in other words, growth observations and pruning weights)
  • Weather conditions
  • Recent inputs to the vines (fertilizers, amendments, irrigation, or vineyard floor management practices)
  • Past experience with the particular vineyard or block.

Interpreting tissue analysis results is not easy because plant mineral nutrition and the impact on vine physiology is complex. If an element appears to be deficient, be sure to look at vine growth. Look carefully for signs of deficiency symptoms. If deficiency symptoms appear, detailed sampling and tissue analysis should be considered.

Do not rely on visual symptoms alone, as symptoms can look similar to other nutrient imbalances or other non-nutritionally related problems (water stress, virus, and trunk disease, for example). Be sure to collect separate samples from asymptomatic areas and symptomatic areas within the vineyard to test and compare whether there is a nutrient deficiency.

Tissue test results indicate the nutrient status of vines, and they can be effective in identifying extremes, whether at levels of deficiency or toxicity. When samples are systematically collected over a period of years, tissue test results can be a valuable tool to manage the nutritional status of your vines and indicate approaching problems.

Issues to consider when implementing a tissue analysis program

Be as consistent as possible

Be as consistent as possible with respect to vine phenology (growth stage) when collecting tissue samples for nutrient analysis. Bloom and véraison are the key time points to collect leaf blade or petiole samples and it is critical to collect samples at the same growth stage each year. Nutrient concentrations in leaves and petioles can change rapidly during the growing season. For example, research indicates that N and P decrease rapidly from bloom to véraison.

Monitor the same areas within specific vineyards or blocks

To do this, designate and flag specific rows within a block that are revisited yearly. This can vastly improve the consistency of tissue analysis and interpretation. Such sampling may be more important in hillside vineyards where there can be great variability in soils across the slope.

If you would like to monitor large blocks with a single sample, then collect petiole or leaf blades in a systematic way across the area and be consistent each year. For example, collect one petiole or leaf blade from a typical vine located every five posts from every 20th row, avoiding rows close to the border of the block (avoid end rows and end vines as they are often more vigorous).

Where to collect samples

Collect and submit separate samples from problem areas where vines are weak or otherwise lag behind, such as low-lying areas or areas of thin soils where vines may develop more slowly over the season due to cooler temperatures or being exposed to varying levels of water and nutrient stress. Be sure to keep samples separate by rootstock or cultivar to allow for the best nutrient analysis and interpretation.

Determine when to collect samples

Sampling is recommended at bloom, véraison, or both. While nutrient analyses will provide a full report for macro- and micronutrients, tissues at certain time points are better at providing information on specific nutrients. Petiole samples taken at bloom typically give a good indication of vine micronutrient status. However, véraison sampling is more indicative of macronutrient status (N, P, K, and Mg). In general, véraison or ripening samples are better to diagnose macronutrient problems because these elements are mobile within the plant or are at very high levels at bloom.

Many people believe collecting samples at bloom will help to identify problems early and correct them in the current year. However, this is unlikely as nutrient analysis takes time, and results need to be interpreted correctly to warrant fertilizer applications. A whole vine nutrient uptake study conducted in Oregon showed peak N and P uptake occurs at bloom and declines thereafter. Therefore, it is less likely that one can affect the macronutrients in the current season; however, micronutrient deficiencies may be amended in the current season with foliar nutrient applications.

It should be noted that foliar applications of macronutrients can be useful to help alleviate severe deficiencies, or in the case with N boost fruit N levels. However, be cautious when using foliar nutrient sprays and investigate what sources are proven to be effective when applied to the canopy.

Which tissue to sample—leaf blade or petiole?

Generally, petiole samples give an indication of K, Cl and Na deficiencies/toxicities. Leaf blade samples give a much better indication of N status than petiole samples, which is also true for Mg, Zn, B, Ca, Cu, and Mn deficiencies or toxicities. Petiole samples are easier to handle and collect in large quantities that provide a good average for the block sampled. The leaf blade is the working organ of the plant and relates better to the physiology of vines. Analyzing both leaf blades and petioles (as separate samples) can be useful to diagnose certain issues and specific deficiencies or toxicities, although it doubles the cost of nutrient analyses.

Collection of tissue samples

Bloom (50–70% cap fall)

For petiole analysis, collect 60–100 petioles from leaves at the same node as a cluster. Cut off the leaf blades, put in paper bags, and get the samples to the lab as soon as possible. Do not place tissues in plastic bags or leave sitting for very long. For leaf blades, collect 20–40, remove the petiole, place in paper bags and submit to the lab immediately. You must submit immediately after collection because leaf blades can form mold much faster than petioles.

Véraison (50% of berries colored/softened)

Collect 60–100 petioles or 20–40 leaf blades in pairs—one opposite cluster and one from a recently expanded leaf from each vine sampled. Treat as outlined above.

Caution: When handling tissues, always be sure to place in paper bags (not plastic) to prevent tissues from remaining moist and developing mold. Ship or deliver immediately to the testing lab to ensure freshness of the samples. If you must wait more than one day to submit samples, be sure to allow samples to air dry (keep in a large paper bag and keep open) before submitting or place in an oven to dry at 50–65°C (125-150°F).

Interpretation of tissue nutrient test results

The following table is based on nutrition research for wine grapes in Oregon with comparison to other regions. Deficient levels for nitrogen (N), phosphorus (P), and potassium (K) are well characterized for Pinot noir. Veraison samples are more reliable than bloom samples for diagnosing most nutrients. Levels from leaf blades at veraison are more reliable than petioles for diagnosing N, P, K and Mg issues.

Tissue Type Petiole Leaf Blade
Nutrient Time of sampling Units Deficient Excessive Deficient Safe/Healthy Excessive
N bloom % 0.60-0.70 2.20 >2.40 4.25
veraison % 0.35-0.40 1.80 >2.00 2.50
P bloom % 0.15 0.17 >0.20
veraison % 0.05 0.10 >0.12
K bloom % 0.75-1.50 3.25 0.70 >0.80 1.5
veraison % 0.5-0.60 0.60 >0.70 1.25
Ca bloom/veraison % 0.9-1.0 0.9-1.0 >1.00
Mg bloom/veraison % 0.20-0.50 0.10-0.20 >0.25
Mn bloom/veraison ppm 20 20 >20
Zn bloom/veraison ppm 20-25 15-20 >20
B bloom/veraison ppm 20-25 125 15-20 >20 250
Cu bloom/veraison ppm 3-5 25-50 3-5 >5

Nutrient considerations

Nitrogen (N)

N can be a limiting nutrient in some vineyards, particularly those on lighter soils with low organic matter. Nitrogen status must be interpreted with respect to vine vegetative vigor and assessment of the visual characteristics of the vine. Even if N appears to be deficient based on tissue analysis, it is not advisable to give N to vines that are already vigorous (showing significant shoot growth and high canopy density). Adding some N fertilizer, using N-fixing cover crops and tilling the soil should only be considered if vines have low vigor and low N levels upon analysis. Excessive nitrogen at bloom has been associated with inflorescence necrosis.

Phosphorus (P)

In most cases, low soil P availability does not always result in low vine P status due to mycorrhizal fungi. However, because P has been shown to be important for flower and fruit formation and differentiation in some cultivars, keep a close watch on P levels. Recent work with Pinot noir has shown that inadequate P did not alter flowering parameters but rather reduced canopy growth and yield. Low P status in Pinot noir was best diagnosed by examining leaf blade P at véraison in that study. Other research has shown that measuring both leaf blade and petiole P at véraison can be diagnostic for understanding P limitation in grapevines because P will generally occur at the same or higher concentration in petioles compared to leaf blades when P is adequate.

Potassium (K)

Low K levels can result from drought, over-cropping vines the previous season, or both. Amendments of vineyard K levels must be approached with care because grape clusters are a strong sink for K. If your vineyard is cropped at very low yields, it is easy to over apply K fertilizer, which may lead to increased pH in berries and musts. High K in musts can also be associated with vigorous, shaded canopies and can be corrected by better canopy management.

Magnesium (Mg)

Mg deficiencies have been somewhat common in western Oregon, particularly in young vines. Many of the red-hills soils considered prime land for vineyards in western Oregon actually have higher Mg levels deeper in the soil profile where older vines eventually access it. Defining better Mg leaf and petiole guidelines for routine bloom and véraison samples will require more research in the region. However, recent cases where severe Mg deficiency symptoms have occurred in both red and white cultivars were diagnosed by leaf blade Mg levels below 0.09% dry weight, while petioles were not able to diagnose the issue (Mg ranged from 0.13% to 0.43% dry weight in petioles).

Boron (B)

Vines in some growing regions have low B due to low levels in the soil. In these cases, growers can apply foliar B sprays to the canopy in spring prior to bloom or post-harvest. It is recommended to maintain these sprays at low doses to prevent toxicity as well as ensuring adequate B.

Zinc (Zn)

Low Zn can be associated with high P and Mg levels in the soil. Foliar Zn sprays may be warranted in spring if deficiency is severe. However, it is important to apply in low doses to avoid toxicity.

Iron (Fe)

Fe is difficult to diagnose based on tissue tests. The form of Fe in the leaf is most important. Tissue tests are typically performed for total Fe and are poor indicators of Fe status. Leaf size is often reduced when Fe is limiting and low Fe can be diagnosed by a combination of interveinal leaf chlorosis (bleaching) and high soil pH. Oregon soils west of the Cascade Range have ample Fe, while soils on the arid east side have low Fe.

For more information

The following OSU Extension publications provide more information on individual nutrient deficiency symptoms and more general information for soil sampling and soil management. See the list of published scientific articles for more detailed information on research conducted in Oregon, some of which is cited in the article above.

OSU Extension resources

Literature cited & research from Oregon

Was this page helpful?

Related Content from OSU Extension

Have a question? Ask Extension!

Ask Extension is a way for you to get answers from the Oregon State University Extension Service. We have experts in family and health, community development, food and agriculture, coastal issues, forestry, programs for young people, and gardening.