The reaction of the grape vine to certain soil-moisture conditions
Thousand of years ago, the Asians and people living around the Mediterranean Sea grew grapes, so the grape vine adapted (adjusted) to do well under hot summer conditions. Although the grape vine is classified as a mesophyte, a plant that grows under moderate moisture conditions, it is well adapted to dry or drought conditions. It is a well known fact that a grape vine uses much less water than a normal deciduous fruit tree.1. Intake of water by the root system:The main reason a grape vine can survive in very dry conditions, is its well-developed and deep rooting-system. Although most of the grape vine's roots is found within the top 400mm of the top-soil, these roots are more evenly spread than those of other plants. Therefore the rule that most of the water withdrawn by a plant happens in the topsoil (40 of moisture in the topsoil and 10 in the subsoil), is not quite true when it comes to growing a grape vine!The withdrawn pattern of a grape vine is much simpler and differs; the more roots, the higher the uptake, whereas depths do not play such an important role.The roots of a grape vine, on sandy or gritty soils, can penetrate the soil as deep as 6 meters (19 feet)!Moisture is take up the quickest in fibril area, just above the active tip of the growing root, and slows down as the older parts of the root system becomes corky. These active tips grow towards the moisture comprising soils, even if it has to grow 6 meters deep!Although a grape vine adapts to these dry conditions, it is not ideal, because once you water your plant, you will have to give much more water to reach the fibril area of the roots. Under normal growing conditions, the fibril area is within that 400mm I mentioned above.Under extreme heat conditions, it is essential that you keep that 400mm well watered.2. The leaf surface (area):During the early stages of the growing season, the leaf surface of the vine is small and transpiration (the lost of moisture through the leaf) is not a big factor. But as the growing season moves on, the total leaf area becomes bigger as leaves grow bigger and much more transpiration will occur. under extreme heat conditions, the vine will transpire more moisture than the roots can take up, and this causes the leaves to look withered (temporary withering). The vine is under a great deal of stress during this stage and you need to lower the temperature of the microclimate around the vine. The only way to achieve that is to apply water, so that the soil temperature will decrease.Normally what happens is, the vine will extract water from all the available sources (roots, stems, shoots and grapes) to compensate for the lost of moisture through the leaves - this has a negative impact on berry size, because the much needed moisture (a grape berry is - 95 moisture!) is extracted from it.One more thing to keep in mind, is that the larger your trellis system or arbor is, the higher the total leaf area will be and of course the higher the transpiration will be. A large growing vine will use much more water in one year, than a small vine because of transpiration.2. The vegetative growth of the vine.Under normal moisture conditions, the vegetative growth of the grape vine will be very high during the start and middle of the growing season but will decrease dramatically as the season goes on and berries start getting bigger. Unlike normal fruit trees, a grape vine will never develop a terminal bud, and will grow as long the circumstances is ideal for growing.You will notice that the active growing points of your vine will have a yellowish/green shine and the older leaves will have a much darker green appearance. One certain way to know that a growing vine is under soil moisture stress, is when active growing points become a dark green color - it is not a red danger sign, but a green danger sign, pay close attention to the growing points of your vine, as they will show you how happy your vine is. Maintaining a good soil moisture throughout the season will ensure a well grown, productive vine BUT a grape vine "hates" wet feet, so don't overdo this (by the way, the symptoms of to little water and to much are exactly the same, so be careful)Danie"The Grape Guy"www.my-grape-vine.com
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