Should you water your grape vine?

Opinion is divided on the subject. I say you shouldn't. Everyone else says you should.

The subject of watering is not as simple as most people think. One mistake that people make is thinking that they have thoroughly watered an area of ground but they have only wetted the top few inches. Plants will root into this surface layer. They become dependent on watering and will suffer if it is not consistent or otherwise inadequate.

Instead of watering little and often, water less frequently but more thoroughly. Don't water a big area every day, water a smaller area using just as much water. You can see if the water has sunk down to lower levels by using a trowel or your hands to dig down. Instead of watering four raised beds each day, water one each day in turn using the same amount of water.

If you must water a vine, do it this way. Infrequently but thoroughly. Use a trickle of water over a long period of time. The water will sink down deep and the roots can follow the water down. Instead of watering the surface, use a vertical pipe to to water into.

If you planted a vine you could at the same time install three vertical pipes. One a foot long near to the vine. One two feet long a bit further away. One three feet long or however deep your subsoil is. In the first year you could water into the short pipe, just to help the vine get established. The next year remove the pipe and water into the second one. The third year water into the longest. Hopefully the roots will grow deep and then it will find its own source of water.

If it is in a greenhouse or against a wall it may never find its own source of water deep down. So watering may still be beneficial. The same rules apply though, infrequent but thorough. I would do it only once; in June, July and August.

I wouldn't plant a vine in a greenhouse. Unless in was something special such as Muscat of Alexandria. Even then you can plant it outside the greenhouse but let it grow inside. They do not need to be protected from winter cold. They don't need high temperatures so in the summer open doors and vents. You can use the greenhouse to get them started earlier in spring and help the grapes to ripen in the autumn.

Some varieties - such as Muscat of Alexandria -  can suffer from fungal diseases like powdery mildew. Keep humidity down: this is achieved by opening doors and vents and also by pruning so you don't get a mass of foliage. Lack of water at the roots can also weaken a vine, so that could be one valid reason in favour of watering.

There are chemicals that can control fungal diseases. Copper compounds don't control powdery mildew, which is the worst of them. Fungi don't seem to like extremes of acidity or alkalinity. You can try sulphur to lower pH or use various sodium compounds to raise it. Just enough to affect the fungus but not so much as to damage the leaf (or your skin). Some people use dilute yogurt: it has to be something with lots of lactobacillus bacteria to increase acidity.

There are modern varieties that are resistant to fungal problems, early ripening so don't need a greenhouse or wall (even for dessert grapes), and have a looser bunch of grapes that don't require thinning. The muscat flavour and the 'strawberry' flavour are delicious.

Muscat of Alexandria and Siegerrebe have a good muscat flavour. Muscat bleu does too and is better in other ways. Fragola is one of the varieties with the 'strawberry' flavour (it doesn't really taste of strawberries - American grape soda tastes of it).

Some people are growing vines in containers. Obviously they will need watering. Feeding too. Otherwise I wouldn't. If I did I would water infrequently but thoroughly and use a low-nitrogen fertilizer once it has become established.

Another factor to take into account is whether you have sandy or clay soil. Mediterranean soils tend to be sandy or rocky, very free draining. What I suspect is that in Britain the deeper roots may die in winter. Then it would only have more surface roots. If so that could be another reason for watering.

People say that vines love watering. If a vine has surface roots only then sure it will respond to watering, and manuring too. You may well get a bigger crop if you irrigate. In California they are depleting the aquifer to irrigate almonds. I'm sure they get a bigger crop.

However almonds and vines can grow in dry conditions and will produce an adequate crop without lots of water and nitrogen. If an almond farmer in California can't make a profit and would go bust without irrigation then something needs to change. Maybe the farms need to be bigger or almonds need to cost a bit more. They are going to have to stop one day, when the aquifer runs out, so they may as well sort out the problem now.