Harvesting rainwater can make your plot’s water supply more secure, but it’s vital to make the water go as far as possible. Smart watering is all about providing just the right amount of water at just the right time, and delivering it exactly where it is needed to waste as little as possible.
Smart watering means not overwatering
Don’t use sprinklers to irrigate your plot if you can help it. Sprinklers are wasteful because they water a whole area rather than just where the water is needed. They’re also too easy to switch on and forget for hours at a time, which can actually harm plants by washing nutrients out of the soil. Instead, get the watering cans out. Even using a hose with a spray nozzle is better than using sprinklers, because you can direct the water to where it’s needed and you are more aware of how much you are using.
With the exception of plants that are still getting themselves established, or newly sown seeds, there is no need to water every day unless your plant is container-grown or in a polytunnel or greenhouse. Instead, actually look at the soil: use a trowel to see what it’s like 15cm down, and only water when things are starting to dry out at that depth. For most soils, a really good soak once a week is enough – less than that if you use mulch. When you do water, water deeply so that the moisture gets down into the deeper layers. Frequent, shallow watering makes plants produce shallow root systems, leaving them more susceptible to dryness.
Water at the right time
The best time to water is in the morning so that the water gets a chance to penetrate right down to the roots before the sun dries it up. Early evening is second best – try to water early enough so the leaves get a chance to dry out before nightfall. Never water in full sun, as the heat means that more of the water will evaporate. Some plants can actually be scorched if they are watered in full sun, as the water droplets act like tiny magnifying glasses, causing damage to the foliage.
It’s not just the time of day that makes a difference, but also the time in the plant’s life cycle. Plants need more water when they are producing flowers or fruit, and a shortage at the wrong time can seriously reduce both the quantity and quality they yield. This includes soft fruits like blackcurrant, gooseberries and raspberries, as well as tomatoes and beans. In contrast, potatoes should never be allowed to run dry when the tubers are forming or they will be small and knobbly. This means that they need to be watered deeply once a week throughout warm, dry weather and always in the morning, as wet foliage is an invitation to blight.
Water roots, not leaves
Plants absorb most of the water they need through their roots rather than their foliage, so try to water the root zone – the soil around the base of the plant – rather than the leaves. This can be difficult for vigorous plants like marrows and squash, and can also be very time consuming if you’re growing plants on a larger scale. For these situations you can use soaker hose (which sweats along its entire length) or a dripper hose. Drip systems use rigid non-leaky pipe to carry the water, and you push ’emitters’ such as drip caps in exactly where you want the water to be delivered. Simple versions of this system such as ‘drip tape’ are inexpensive enough to be practical for long rows of plants and last for several years. Both soaker hose and dripper systems should be covered with soil or mulch to help the water spread out, and to reduce evaporation.
Use mulching to reduce water loss
Mulch can reduce evaporation from bare soil by up to 70% by protecting the surface from dry air and wind. Mulching materials can include chunky bark chips, sawdust, sheet plastic and even flagstones, but what you choose is less important than the fact that you are doing it at all. Mulched areas need watering less often than areas which have not been mulched, but they still need to be watered deeply when you do irrigate them.
Don’t water the lawn
Unlike other plants, grass goes into a state of dormancy when the soil dries out too much for growth. It revives once water becomes available. This means that it’s OK to let your lawn go brown, except areas which have to take heavy wear. Frequently-walked areas such as round children’s play equipment may become bald in a drought, so these small areas may need to be re-seeded in the autumn unless they are watered once a week or so during prolonged dry spells.
If you are seeding new areas, choose a grass mix that is drought resistant. Kentucky Bluegrass recovers quickly after long dry periods, and deep rooting Tall Fescue draws its moisture requirements from much deeper in a soil than any other lawn grass. Throughout dry periods avoid cutting lower than 2.5cm (1″) in height. Feeding lawns may strike you as being a waste of nutrients, but if your land is prone to drying out an adequately-fed lawn will withstand dry weather better than one which is crying out for nutrients.
Choose plants that will put up with dry conditions
If your soil is shallow or poor, you can save yourself expense and heartache by choosing plants and varieties that will cope well with dry conditions once they are properly established. There is lots of advice available concerning ornamentals (largely from firms hoping to sell the plants to you). Information on edibles is harder to come by, but it is worthwhile checking the plant list at the Agroforestry Research Trust in Devon, which makes a point of mentioning drought resistance for many plants.
Build your soil
Any time the soil is bare, build the soil by adding lots of organic material such as compost or manure. Sandy soil benefits from lots of organic material because it acts like a sponge, holding onto nutrients and preventing it from drying out so quickly. Clay soil benefits from lots of organic material because it helps open the structure of the soil out, stopping it from drying into impenetrable brick so easily. Even marsh plants that demand lots of moisture round their roots, like celery, will withstand dry weather better if they are planted on top of a good layer of moisture-retaining compost. The exceptions to adding organic material are root crops like carrots and parsnips, which need lower nutrient levels to produce fat, straight tap roots.