Drought: how to adapt in the garden

Bunny Guinness from the Telegraph: We’re nation of weather watchers, and the gardeners among us are getting extremely concerned. Even if we get a drenching this month, the hosepipe ban in many areas looks set to stay for the summer. It’s time for a rethink about the way we use water in the garden.

Talk to gardeners in Portugal and Spain and they think we are a bit of a joke — they grow amazing vegetable crops and have glorious gardens on far more paltry rainfall than ours. We have got used to sloshing water around and so are worried when we are told not to use sprinklers. But these things can whoosh 1,500-2,000 litres of water into the air per hour. Most evaporates, more trickles to places it is not needed, away from the plants’ roots, and what does fall by a plant will tend to sit on the top and encourage the plants roots to the surface of the soil – exactly what you do not want.

The water ban varies for authorities, but most do let you use “drip or trickle” irrigation systems which are on a timer. These systems typically discharge 2l per hour from each drip (positioned about 30cm apart). Water is drawn sideways and down within the soil. Such systems are invaluable for faster hedge establishment or when you are planting big plants, but generally most people recognise that after plants are established you really want them to survive on their own. The choice of such plants is staggeringly large. Dr Ross Cameron of Sheffield University used to work for Defra, experimenting on how reducing water regimes could be used by commercial shrub nurseries to produce more compact, floriferous plants.

The physiology of Plants

He has observed how the whole physiology of plants changes when you cut down on water. Plants respond by closing their stomata (pores on the leaf where oxygen, other gases and water move in and out) for much longer during the day. They cannot make so much energy and so growth is reduced, but they survive. As long as you slowly wean a plant onto a drier regime many of them will adapt to these drier conditions and still look fine. They will just not put on new growth.

Commercial Growers

Commercial growers use this information and instead of producing vigorously growing shrubs with one or two straggly shoots, the lower water level gives rise to better plants with tighter-knit growth and more flowers produced closer together. Cotinus and Buddleia are good examples: they react very quickly to lower water levels, they shut down their system and can tolerate dry periods for some time. New leaves (if any) that are produced will be smaller and closer together.

Different Plants

Different plants have different tolerances though, so watch your range – and if any choice plants are really flagging give them any spare water. The old saying, “The shadow of the gardener is the best manure” certainly applies here. Many gardeners think you cannot produce good crops without extra water, but some plants are surprisingly drought tolerant. Herbs produce aromatic oils. Drier conditions mean even more oils are produced, making them more flavoursome. With vegetables, although higher water levels give higher yields and larger, more handsome specimens, this does not equate to greater flavour. If you are going to water, when you do so makes a difference. Trials carried out by what was formerly the NVRS (National Vegetable Research Station) give useful information. They found that summer cabbage (extremely sensitive to water shortage) watered 11 times increased the yield 100 per cent, watered twice increased it by 80 per cent yet only one watering two weeks before harvest improved yield by 65 per cent.

Beans are best watered at the start of flowering and, if you water during pod forming, it improves pod set and quality. Four gallons per square yard once a week, if dry, will help apparently, but in my “desert” garden in the East Midlands, I may soak them three times maximum during a dry summer and still get more than enough beans. Climbing French are generally better in dry conditions than runner beans.

According to the NVRS, lettuce, courgettes, spinach and new potatoes do respond to frequent watering, but most of us have gluts in these and by cutting down on water you can get tastier, adequate crops. Carrots, broccoli, sprouts, leeks and onions are not that responsive to watering once established. But the NVRS recommended watering sweetcorn at the tasselling and cob swelling stage, if dry.

Water

If you have little time and water, applying bulky organic matters will increase your soil’s ability to hold water. Adding a thick mulch after watering will not only save water, but increase the beneficial earthworm population. Keep on top of weeds to prevent water competition from their roots too, but don’t hoe as this encourages evaporation.

Biochar

Biochar, from Carbon Gold (carbongold.com), is a non-bulky material that increases the soil’s capacity to hold water (and minerals) and can make a big improvement to soil structure. When you do water, it is rarely worth applying less than two gallons per square yard (although directed to rows/plants) unless watering in transplants. For high-water-demanding crops, such as celery, grow in a large pot with a saucer under and keep some water in reservoir. Pick around plants to give continuous yields.

There are pitfalls with watering too. Root crops can produce unbalanced, lush foliage if given too much. If you water many root vegetables after a dry period you may well get splitting. In droughts I always think of a tip from an irrigation adviser who was working in Greece. There they soaked the beans when they went in and then ignored them, and despite really hot temperatures with no rain they all cropped well. The roots followed the initial water down and then the plants can fend for themselves. Hopefully, gardeners will adapt to our “low water regime” too and may even have better tasting veg and well adapted plants.