Plants need to be watered correctly. There should be enough to wet the top 30cm (12in) of soil, where most plants’ roots should be. Too little water just wets the soil surface and either does not reach the roots or encourages them upwards where they tend to dry out.
Too much water will drain out of reach of the roots, or waterlog the soil causing root rot. It is therefore important to manage the flow of water around a garden.
Our Water Management Scientist has launched a survey to find out what you would like to know about watering, with the intention of focusing her future research on addressing the most popular reponses.
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Harvesting the rain
Traditionally, for many gardeners, the collection of rain has been limited to a water butt or two. A typical water butt holds about 200 litres (44 gallons), just enough to keep one medium-sized container of bedding blossoming all summer.
Even with regular rain topping them up, it is clear that as many as half a dozen water butts are unlikely to meet all of a gardener’s watering needs during dry spells and hot summers.
One solution is a domestic rainwater-harvesting system, which can easily fill an underground tank holding 6,500 litres (more than 30 ordinary water butts) from the roof of most homes.
A specialist system of this size costs about £2,000, plus about £500 to install. Needless to say, this is not a quick saving on water bills at current prices, but it can be seen as insurance against hosepipe bans, or simply an environmentally responsible act.
It would be better to fit such systems when houses are built. There is some encouragement in the UK Government’s voluntary Code for Sustainable Homes, which awards a star rating for environmental credentials. However, there is little evidence of builders taking up this challenge, yet installing a system while building would save a few hundred pounds compared with the price of fitting one later.
Gardens can soak up the rain unlike paving, tarmac and concrete, which are less porous and increase the amount of rainwater that runs off by as much as 50 percent. This additional water usually flows into street drains, which can’t always cope, and excess water can then go back up people’s front drives to flood their homes. To avoid this problem, use permeable paving and keep hard surfaces to a minimum.
Find out more about permeable paving
While overwatering can be corrected, waterlogging and flooding are more of a problem. If they happen in winter, when most plants are dormant, the damage can be easily missed, but with summer floods, symptoms such as wilting, yellowing and browning of the leaves usually appear rapidly. Either way the roots suffocate, drown and rot, and the conditions are right for diseases such as Phytophthora.
Where waterlogging is known to be a problem, there are ways to improve the growing conditions. Using raised beds and planting trees and shrubs on mounds helps to lift roots above water tables that are near the surface, and provides some protection against flooding.
Poor drainage on clay soils can be improved by cultivation. Similarly, water lying on lawns can be encouraged to soak in by spiking and topdressing with sand to create mini-drainage channels.
In the worst cases, you can lay perforated plastic drainage pipes in the ground to move water to soakaways and ditches.
Tips on saving water
- Preparing the soil in autumn or winter reduces moisture loss compared with summer cultivation; applying a mulch in late winter will help lock in water.
- Digging in organic matter such as well-rotted garden compost retains extra moisture and can provide plants with the equivalent of an additional 5cm (2in) of rain: about 20 days’ supply for many common garden plants.
- Deep, double digging or using raised beds also increases the volume of soil into which plant roots can spread and draw moisture.
- Many measures are common sense: put saucers under containers to catch runoff, remove all weeds (they use water, too) and use ‘grey water’ where possible.
- Increasingly sophisticated automatic irrigation controls are available to the home gardener, with sensors that turn off the water when it is raining, or when the soil is too moist, though the accuracy of soil-moisture meters will depend on the soil type and on careful positioning of the probe.
See practical tips on designing and planting a garden to manage water effectively.
Few garden plants will survive prolonged periods in ground saturated with water.
Read our advice below for care tips and plant choice.