Do you need to fertilize this year?

Wednesday, July 26, 2023

Many growers are wondering, now that they see canopy growth, in some cases with what appears to be full canopies with some potential crop to be harvested, whether they should be adding extra fertilizer especially if they did not fertilize in the spring. I am writing from my perspective on vine physiology and growth rather than as a supplier of inputs.

The tendency is to add fertilizer thinking the crop needs it to mature. This can be a false assumption as there are very few blocks that have a crop of 75% of normal or greater.  It is better to look at how the vines are currently growing before adding extra nutrients at this time of year.

Most vineyards I have visited that will be having a crop this year appear to have a full canopy but upon closer inspection the number of primary buds that survived were close to original estimates with the bulk of the canopy comprised of secondary and tertiary buds. A number of vineyards may actually need some hedging to keep the vines in check – this tells me they are not hurting for nutrients so adding anything more would only add fuel to vegetative growth and likely delay crop maturity and reduce winter hardiness and acclimation this fall.

There is need to look at crop balance relative to vegetative growth and where there is no crop to avoid excessive vegetative growth late in the season. For blocks with limited growth or growth around the head or from suckers adding extra nutrients is only likely to stimulate the development of bull wood or excessively thick canes which as above mature poorly and have reduced winter hardiness and are slow to acclimate in the fall.

If you have prior information from soil and or tissue tests in the past couple of years would be my starting point to assess vineyard nutrition.  The soil is like the food at the buffet, it lets me know what is available to the plant and how much there is, but it does not tell me what the plant is actually taking up.  Tissue tests can tell me what the vine is “eating” but you must remember they are only a snap shot and the results can be skewed by the time of year taken, the cultivar, the rootstock (if used), climatic conditions at time of sampling (hot, dry, wet , cool) and what stage of growth the vine is at/or nearing ( bloom is very stressful and again can result in apparent deficiencies if tested at that time but if tested a few weeks later results are in the normal range). 

Just adding extra or unnecessary micronutrients or even macro nutrients to a “no harm” philosophy can also cause problems. Many nutrients, if excessive, can result in other necessary nutrients being blocked out (magnesium, potassium and calcium come to mind) which can lead to bigger problems.  I prefer to look at it as the vineyard is a circle of life. We want to reach the point where we only need to add what has been taken away from the site (that is harvested fruit). 

Most growers mulch pruned wood and most leaves that have absorbed nutrients fall and rot in the vineyard returning to the soil. Yes, some extra nutrients are needed during the early phases of vine establishment to grow new roots, expand the trunk, and allow for vine size increase but once a vine is several years old the assimilation of elements is not as much as one might think.  As the roots of the vine expand horizontally and vertically, they are accessing soil reserves that have been untapped.

A little known fact is in general terms, soil covering one acre, 6 inches deep (15 cm) weighs approximately 2 million pounds (900,000 kg). Add to this that the bulk of feeder roots in a vineyard are about 18 inches (50 cm) out on each side of the vine and to a depth of 12 to 15 inches (30 to 40 cm), with anchor roots and depth roots going deeper and wider but are not key nutrient absorbing roots.

If you think of your fertilization practices where some years you might apply 200 lbs. per acre (100 kg per ha) of 34% N (68 pounds of active N per acre or 34 kg of active N per ha). If evenly spread, you are not adding a lot of material, but you can elicit a huge vegetative response if there is no crop present to help take it up.

Below is a quick chart of nutrient removal per ton of grapes harvested.  





























7 g

15 g

30 g

2.5 g


This is not a lot of crop removal of nutrients.  You can take those numbers and double them to allow for vine uptake for canes, leaves, shoots trunk and root growth and vine development means not a lot is required by the vines especially if no crop is present. My instinct is that for most of the vineyards in Nova Scotia for 2023 there is more than ample available nutrients for the vines to properly grow, mature and acclimate and the additions of extra fertilizers is not really needed!

So, before I would apply any nutrients this year, I would want to see visible symptoms of deficiencies and If I did, I would only then treat with foliar applications to keep the vine in balance and NOT promote excessive growth or compromise my vine maturity and winter hardiness gong into winter 2023/24.  If you are looking for pictures of symptoms of some deficiencies check out the Perennia Q&A session on July 27, 2023, and/or access the information from the session online. If you have more questions, feel free to contact me via with specific questions or we can arrange to talk on the phone before my next visit to Nova Scotia the week of August 14!  

To learn more on this topic or to see pictures of symptoms of deficiencies please join us this Thursday for a Q&A July 27, 12pm - 1pm

Register here in advance for the upcoming Q&A with Dr. Kevin Ker.  After registering, you will receive a confirmation email containing information about joining the meeting.  If you can't make it but would like to submit questions, email us and we will post the recording after for your viewing pleasure.

Please click the link below for the Q&A recording July 27, 2023. "Do I need to fertilize this year?" with Dr. Kevin Ker.

July 2023 Viticulture Q&A - YouTube