Conserving Water in the Garden: What Actually Works

There is a version of water conservation that consists of feeling guilty and watering less. It does not work. Plants that are underwatered for weeks and then rescued with a heavy soak are more stressed, not less, and a garden watered nervously often uses more water in total than one watered properly.

What actually works is getting more of the water you use into a root, and less of it into the air, the path, and the top two centimetres of soil. Here is what makes the difference, roughly in order of how much it matters.

Water deeply, and much less often

This is the one that changes everything, and it is the one most gardeners have backwards.

A light daily sprinkle wets the surface. The surface then dries out within hours, and the water is gone before it has reached anything. Worse, roots grow towards water — so a plant that is watered lightly and frequently develops a shallow root system concentrated in exactly the layer of soil that dries out first. You have trained it to be fragile, and every day you miss becomes a crisis.

A thorough soak once or twice a week does the opposite. The water penetrates to depth, the roots follow it down, and the plant becomes progressively less dependent on you. The soil at 20 or 30cm holds moisture for far longer than the surface, because it is insulated from sun and wind.

In practice, for an established shrub, that means something like 10–20 litres delivered slowly in one go, rather than a can splashed round every evening. For a border, it means moving methodically along it and giving each plant a proper drink, then not returning for several days.

The way to check is to push a finger, or better a trowel, into the soil an hour after watering. If it is damp for the top centimetre and dust below, you have wasted your time. That test is more useful than any watering schedule.

Water at the base, not over the top

Water applied to foliage mostly evaporates. Water applied to the ground goes where it is needed.

Aim the can or the hose at the soil at the base of the plant, and let it go in slowly enough that it soaks rather than runs off. Baked ground is surprisingly water-repellent, and a fast pour on dry soil will run sideways and disappear down a crack having wetted almost nothing. If water is pooling and running, stop, let it soak, come back and add the rest.

Two tricks that help on hard ground:

• Sink a pot or a pipe. A plant pot pushed into the soil beside a shrub, or a length of pipe set vertically at planting time, gives you somewhere to pour that delivers water straight down to the root zone instead of across the surface.
• Build a shallow basin. A low ring of soil around a plant, 30–40cm out from the stem, holds a full can in place long enough for it to sink in rather than run off. This is standard practice in hot countries for good reason.

Overhead sprinklers are the worst of all worlds even when they are permitted: a large proportion is lost to evaporation and drift, and what lands is spread evenly over ground that mostly has no roots in it.

Get the timing right

Water early in the morning or in the evening. Both are considerably better than the middle of the day, and the water companies themselves recommend the cooler parts of the day for exactly this reason.

Early morning is marginally the better of the two. The soil is at its coolest, evaporation is lowest, and foliage that gets splashed dries during the day rather than sitting wet all night — which matters for anything prone to mildew or botrytis. Evening watering is a close second and is often the only realistic option for people who work.

The middle of a hot day is genuinely wasteful. A substantial share evaporates before it does anything, and you will need to water again sooner.

Bath water, washing-up water and the rules for using it

Greywater — water from baths, showers and washing up — is one of the largest untapped sources in most houses, and it is not covered by hosepipe restrictions, because it is not coming out of the mains at the point you use it. A single bath is 60 to 80 litres, which is a great deal of border.

Water companies are relaxed about it and set out sensible limits. Southern Water's own guidance is a good summary of the consensus: plants can be watered with shower, bath and washing-up water; it may contain soap and detergent, but soil and potting compost filter those out effectively and the residues can act as a mild fertiliser.

The rules that come with that are worth following properly:

• Use it within 24 hours. Stored greywater goes off quickly and starts to smell. Collect it and use it the same day.
• Do not put it through an irrigation system. Greywater carries fats, hair and fibres that will block emitters and drippers. Apply it by can or bucket only. This is explicit in water company guidance and it is also just practical.
• Keep it off edible crops. The risk is pathogens rather than detergent, and it is not worth taking on anything you are going to eat. Ornamentals, shrubs, lawns and trees are all fine.
• Avoid it on ericaceous plants and seedlings. Soapy water tends to be alkaline, which is the wrong direction for camellias, rhododendrons and blueberries. Young seedlings are more sensitive than established plants.
• Prefer bath and shower water to washing-up water, and avoid anything with bleach, disinfectant, dishwasher salt or water softener in it.

Getting it out of the house is the real obstacle. A bucket in the shower catching the warm-up water is the easiest start — that is clean water that would otherwise go straight down the drain, and there are no restrictions on where it goes.

Cut the demand, not just the supply

The last category is the one that keeps paying after this drought ends.

Mulch. A proper depth of bark or compost over damp soil dramatically cuts evaporation from the surface, and it is the single most effective structural change most gardens can make. It is worth its own article, and it gets one later in this series.

Group thirsty plants together. Containers, new plantings and anything genuinely demanding in one place means you water one area properly rather than walking the whole garden. It also means the rest can be left alone with a clear conscience.

Deal with containers separately. Pots are the real water sink — a container has a tiny soil volume, no groundwater to draw on, and dries out from the sides as well as the top. Move them into shade for the duration, group them so they shade each other, stand them in saucers, and accept that they need watering when the ground does not.

Let the lawn go brown. This is the hardest one to accept and the easiest to act on. An established lawn going brown in a drought is dormant, not dead, and it greens up within a fortnight of proper rain. Watering a lawn through a drought consumes an enormous volume of water for a purely cosmetic result. Raise the mower blades, stop mowing when growth stops, and leave it.

Plant for the conditions you now have. The largest saving is a border that does not need the water in the first place. Our drought and dry soil listings are a reasonable place to start, and autumn — not now — is the right time to plant them.

None of this requires equipment or expense. It mostly requires watering less often and much more thoroughly than feels natural, which takes a few weeks to get used to and then becomes obvious.