Before you read any further, I want you to understand that this blog post is a guideline only.  What I will do, is to recommend what you should do with post harvest irrigation, and since the messo and macro climate of each region differs, you must adapt what you learn here, to suit your own needs.

I will start by saying that many grape growers stop watering their grape vines, once the crop was harvested – BIG MISTAKE!.  Ask yourself this question; “Why would you stop watering your grape vine?”  Because there are no fruit on the vine anymore?  Is it only the fruit that use water?  Certainly not …

If you think back at how you watered the grape vines in spring, with the fist signs of bud break, you probably started watering the grapes because you know the vine will start to use some water.  Back then, there were no visible grapes on the vine, and the roots of the grape vine just came out of dormancy.

Without digging too deep into the subject, it’s just logical that you will that your grape vines will become more stressed and the need for water will increase as the average temperatures rise, the shoots from the vines grow longer and the canopy area increase in size.  The increased temperature and canopy size will result in higher transpiration figures and the vines itself will use more water as the grapes start to develop and gain in size.

Now, after you have removed the grapes, the vines will have much less stress and at the same time the need for water will slowly decrease.  The important thing to remember is that the grape vine don’t stop using water after you harvested the crop – it only needs less water.

As fall approach, the days will be getting shorter and the average temperature will start to drop.  The grape vine will get ready for winter and starts going dormant, but still the vine is active!

The key thing to remember here is; that the longer you can keep the green leaves on the vine, the longer carbohydrates will be assimilated.  And for this to take place, the grape vine needs a source of energy – water.  The longer the assimilation of carbohydrates take place, the better the shoots of the grape vine will ripen, making the grape vines more cold hardy.  I’ve heard of people in cold climates who strip the leaves from the vines to prepare it for winter – this is NOT recommended.  In fact, your grape vines will be less cold hardy if you do so.

This however is not true in tropical climates.  Remember, that in the tropics, the daily average temperature will not drop low enough for the vines to go dormant and it is a well known practice that in these climates, grape growers remove the leaves from the vines to “force” the grape vines to go dormant.

To sum up what I’ve just said, have a look at the following graph.  This shows a pattern or curve of when the grape vine needs most of it’s water.

This shows a drastic increase in the water usage and a decrease once the grape crop has been picked.

Don’t stop watering the grape vine after harvesting the grapes, slowly cut back the water until the vine is fully dormant (normally the end of fall).  When the vine is fully dormant, it needs very little water and 90% of the time, you don’t need to water the grape vines during dormancy - except if you have very dry winters.

I hope this article makes sence and you now understand why post harvest irrigation is VERY important.

Take care,

Danie

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