Fertilize your grape vine

Published: 13th August 2008
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In general, the grape vine needs less fertilization than an annual plant, but there is also a misconception that a grape vine needs poor soil, to do well. To be able to produce top quality grapes and to have a strong enough growth, the grape vine needs certain nutrients that are essential. Without enough of these nutrients, at a specific time, the grape vine will not perform and will not have optimum production, as it should.

Small amounts of nitrogen (N), phosphorus (P) and potassium (K) is needed for the wellbeing of the grape vine. The roots of the grape vine spreads well under normal conditions and the assimilation of these elements are quick; maybe this is why most people think a grape vine NEEDS poor soils - not true, although a grape vine will survive on poor soils.

Many of the nutrients needed next year, become available to the vine when you leave the pruned shoots and leaves on the ground. These pruned shoots, leaves decompose and release the nutrients to the soil, and this is why it is not easy to determine the real basic nutrient needs of a grape vine.

The actual requirements for a grape vine varies according to the production potential and are influenced greatly by climate and weather conditions, therefore you should have a soil sample taken beforehand, although a tissue sample is much more accurate than a soil sample. The following are only estimates and should be used in conjunction with a soil or tissue sample.

Macro elements

1. Nitrogen (N)

Spread N-fertilizers widely over the whole area where the root system is developed. In order for the plant to have access to the N, you will have to mix the fertilizer with the top soil or you will have to wash it in by watering the vine. Young vines' root system are small, so you will have to concentrate the fertilizer on the area where the roots are. Remember that a young (small) vine needs less N than a fully-grown vine.

All ammonium-(NH4) fertilizers have an acidifying effect on the soils and over a period, it will raise the pH of the soil. This effect neutralizes with periodic lime applications.

Because N-fertilizers are highly soluble, the leaching of N is quite high on irrigated soils, you must take special care when applying these fertilizers. There are three stages during the growing season of a grape vine we need to apply N to the soil and they are during spring (just after the first shoots become visible), after flowering (when fruit set was initiated) and post-harvest (after all the grapes were removed).

The grape vine uses N, accumulated inside the roots of the vine during winter, to sprout. For this reason, we apply a post-harvest N-application and because this is the time when there is a peak in the assimilation of N.

The amount of N a vine needs vary on different soil types but it should not be more than 60 gram of N per year. Observed the vine closely, adjusting N rates according to vine vigor and production.

Excess N in the soil will have a huge impact on the productivity of the vine; because the vine will grow too vigorously and poor bud, fruitfulness will occur. Excess N will result in excessive berry drop, bud necrosis and bunch rot. For this reasons you NEVER should apply N-fertilizers during bloom or near berry coloring - this is important!

Sprout our bud break - 25 gr
After flowering - 15 gr
Post-Harvest - 20 gr

2. Phosphorus (P)

The application of P-fertilizers my be localized and not spread out. This will ensure a much higher assimilation of P by the grape vine. P is not very moveable in the soils and it is therefore necessary to work these fertilizers into the ground. The vine needs little P per year and an application of P-fertilizer can be applied once every 3 years. You will need a soil analysis to determine the available P in the soil.



3. Potassium (K)

Normally potassium chloride is used to ad K to the soil, because it is the cheapest K-source. The K concentration in a grape vine can range from 1% to 4% on a dry weight basis. Sandy soils are usually low in K so take special care when preparing the soil before planting.

The best way to correct K deficiency is to apply 1 to 2 pounds potassium sulfate (K2SO4) to the soil. Applying potassium sulfate through the irrigation system shows much better results than a normal application by hand, and if this is impossible, you should try to apply it close to the roots of the vine (deep application).

When using potassium nitrate, the nitrogen content must be considered and must be added to total N you will apply to the soil.

Apply K after bloom, but before berry coloring (veraison).


4. Magnesia (Mg)

Mg is the only element that is part of chlorophyll so it is very important for photosynthesis. A lack of Mg normally occurs on the older leaves first and is normally visible during of near coloring of the clusters. The symptom of an Mg shortage is the yellowing of the leaves between the nervures on white varieties and red coloring on red varieties.

The lack of Mg normally occurs on sandy soils with potassium layers in the subsoil. An overdose of potassium can cause Mg absorption to stop and the symptoms will look like an Mg shortage, but in the meanwhile, there is a K overdose. A well-balanced Mg / K ratio is therefore important.


Microelements

Microelement shortages are normally corrected with foliar fertilizers.

1. Zink (Zn)

Zn is essential for carbohydrate- and protein metabolism.

Symptoms of Zn shortages are firs visible on apical leaves. The symptoms are almost the same as those of Mg shortages, but with one difference, the area around the nervures will stay green and do not get a yellow color. The leaves of the vine stay small and the growth of shoots is very little. In some cases of Zn poisoning, the vine will abort berries and the berries will differ in size.


2. Boron (B)

A grape vine needs very little B about 2/3 oz/vine every 3 years. Be careful of applying B-fertilizer, because B-toxicity can ruin your vine!

Boron is normally applied as a foliar fertilizer and should be sprayed 2 to 3 weeks before bloom with a soluble boron (20% B) spray product.


3. Copper (Cu)

Cu form part of certain oxidation-enzymes and very little is needed for normal functions in the grape vine.


4. Manganese (Mn)

The main purpose of Mn in the vine is to active enzymes needed for photosynthesis, and therefore plays an important role inside the vine. Mn is not very movable inside the plant and symptoms of a Mn shortage will be visible on the older leaves on the vine. Just like Mg and Zn, the leaf will develop a yellowish color around the nervures of the vine, but with one difference from the previous two - secondary nervures stay green!

All of the other microelements that you will find in a vine is needed in such small quantities, that I seldom even think of them. The only way you can really see if you have a shortage of these microelements is to do a leaf analyses, but this usually is not necessary.

Do not pay to much attention to the fertilization of a grape vine, as it needs not much. Keeping the optimum levels of N, P, K, & Mg, Mn and Zn, can be obtained with a well-balanced fertilizer and is normally enough for the home grape grower.

Over fertilizing is a much bigger problem than under-fertilizing and if you vine grows too vigorous, cut back on that fertilizer a bit. Remember a too vigorous growing vine can lead to unfruitfulness, especially with cultivars like Sultana and Crimson.


Video Source: Youtube

Comments
George on September 13, 2011 said:
Grapes I have produced have been of much higher quality since taking the advice from this article. The location you grow them in is also an important factor.
Amy on May 8, 2012 said:
Grapes grow best when they are planted in soil with a pH between 5.0 and 6.0. Fertilizer is helpful, but it should only be used when necessary. Applying fertilizer to a grape arbor when it is not necessary can actually do more harm than good
Barrie on May 8, 2012 said:
I recently retired to Cyprus and have started to grow grapes around my villa, I am really looking forward to turning the grapes into my own wine, but its all new to me.

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