Most gardeners water too often and not enough. A daily splash from a can wets the top couple of centimetres, evaporates by lunchtime and teaches roots to stay near the surface, which is exactly the wrong habit in a dry August. The RHS puts it plainly: water less often but more thoroughly, then let the surface dry before watering again.
Deep and infrequent beats little and often
The target is to wet the soil to 15 to 30cm, which is where the working roots are. That encourages plants to root deeply and makes them far more drought tolerant when a hot spell arrives.
Some arithmetic makes the point. One millimetre of water over one square metre is one litre. A standard 9 litre watering can spread over a square metre therefore delivers 9mm, which soaks in a few centimetres at most on ordinary soil. To wet a square metre properly you are looking at something closer to 20 litres in one go. Two full cans on a square metre once or twice a week does more for a bed in July than half a can every evening, and takes less of your time.
Timing helps too. The RHS recommends watering early in the morning, when less is lost to evaporation and the plants can use it through the day. Water at soil level rather than over the foliage, which reduces fungal disease. And a watering can is the most efficient tool there is: sprinklers waste the most water of anything in the garden.
What actually needs watering
Less than most people think. The RHS position is that established trees, shrubs and perennials generally need watering only in extreme drought. What genuinely needs it is anything planted this season, anything in a container, and thirsty crops in fruit.
| What | How often in a dry summer |
|---|---|
| Containers and hanging baskets | Daily, sometimes twice on a hot day. They have nowhere to draw from |
| New plantings, first season | A thorough soak once or twice a week through the first growing season |
| Fruiting crops: tomatoes, courgettes, beans | Regular and consistent. Erratic watering causes splitting and blossom end rot |
| Leafy crops and salads | Keep the soil evenly moist, or they bolt |
| Established trees, shrubs and perennials | Only in extreme drought |
| Lawns | Not at all. Brown grass recovers when the rain returns |
Sizing a water butt
Rainwater is free, better for plants than treated mains water, and the RHS treats storing it as a straightforwardly sustainable way to use resources, with mains water as a last resort. Working out how much you can collect is simple.
The same conversion applies: 1mm of rain on 1m² of roof gives 1 litre. Take a small garden shed with a roof footprint of 3m by 2m, so 6m². In a part of the country receiving around 700mm of rain a year, that roof sheds roughly 6 × 700 = 4,200 litres over twelve months. Annual rainfall across the UK varies enormously, from the drier east to the far wetter western uplands, so look up the average for your own area rather than assuming.
The point of that sum is not the annual total, which is always far larger than any butt can hold. It is that supply is never the constraint. Storage is.
Now size it against demand. A 3m by 3m vegetable bed is 9m². At roughly 20 litres per square metre per thorough watering, once a week, that bed wants about 180 litres a week in a genuinely dry spell. A single 210 litre butt therefore covers a little over one week of no rain at all. Two butts linked together cover a fortnight, which is the length of most British dry spells. That is the calculation to do before buying, and it usually argues for more capacity than people expect.
Practical points: raise the butt high enough to get a can under the tap, fit a lid for safety and to keep light out, link overflow to a second butt rather than back into the drain, and site it under a downpipe rather than somewhere convenient.
Mulch does more than watering does
A layer of organic mulch about 5cm thick conserves moisture by slowing evaporation from the soil surface. It also suppresses weeds, which are competing for the same water.
The timing matters. Mulch onto soil that is already wet, ideally after a decent spell of rain in spring, because mulching dry ground seals the dryness in. And keep it off plant stems and tree trunks, where it holds damp against the bark.
Improving soil with organic matter over several years does the same job more permanently. A soil with good crumb structure holds far more available water than a compacted or structureless one, which is one more reason the advice in our soil article keeps paying off.
Hosepipe restrictions are local, not national
There is no national hosepipe ban in the UK. Restrictions are imposed by individual water companies over their own supply areas, which is why one town can be under a ban while the next county is not.
That means the only reliable source is your own water company's website, and it is worth checking rather than relying on what you read about somewhere else. Where a restriction is in place, watering cans are normally still permitted even when hosepipes and sprinklers are not, and stored rainwater is generally outside the restriction entirely. Read the specific terms, because they vary between companies.
Greywater, meaning water from baths, showers and washing up, can be used on ornamental plants. Use it fresh rather than storing it, keep it off edible crops, and avoid water containing bleach or strong cleaning products.
Planting so you water less
- Choose plants that suit the site. Mediterranean herbs, lavender, sedum, thyme and many silver-leaved plants are built for dry ground. Putting a moisture lover on a hot sandy bank creates a watering job that never ends.
- Plant in autumn where you can. Autumn planting gives roots months to establish before the first dry summer, which halves the watering in year one.
- Group by thirst. Keeping the thirsty things together means you water a small area properly rather than the whole garden badly.
- Use bigger containers. A small pot dries out in hours. A large one holds a reservoir, and the difference on a hot weekend away is a plant that survives rather than one that does not.
- Sink a pipe or a pot next to hungry crops. Watering into a buried pot beside a courgette or a tomato delivers water to the roots instead of the surface, where most of it evaporates.
This is general growing information rather than advice for a particular garden, and rules on water use are set by your water company rather than nationally, so check locally before assuming what is permitted. The RHS publishes fuller guidance on watering and on drought-resistant planting, and our garden planner will help you group beds by what they will actually need.