10 ways your garden can help reduce flash flooding

Long periods of drought leave the ground baked rock hard and impenetrable, meaning there is a risk of serious flash flooding. The risk can be reduced with clever garden planning in urban, high tarmac areas, and the RHS is calling on British gardeners to look at what changes they can make to their garden to handle the increasingly temperamental British weather, and you don’t need to completely revamp your garden to make a difference.

Here, Guy Barter, the RHS Chief Horticulturalist, shares his top tips for making your garden work with the changing climate.

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Every garden helps

You might be thinking that one garden can’t make a difference, but if every garden on a street was optimised to retain rainwater the chance of a sudden flood would be greatly reduced, so try to do what you can and spread the word. "Some people don’t realise the massive role that gardens play in reducing the risk of flooding," says Barter. "Rainwater needs somewhere to go, so if it’s not soaked up or captured in some way, it’ll usually flow into street drains which can’t always cope with the thousands of extra litres in a storm so may result in flooding."

“Greening grey Britain is our call on the nation to plant up grey spaces, and by conserving rainwater in our gardens and green spaces we can help reduce flash flooding. On its own one garden with opportunities for rain to soak in or be temporarily held rather than flowing into the street might not make much difference but together many gardens optimised to retain rain water will greatly reduce sudden floods.”

Make sure you have gutters

“Rainwater can be collected from the roof of homes, garages, greenhouses and other garden structures as long as they have gutters and a drainpipe,” says Barter. In fact, even in dry areas, it is estimated that around 24,000 litres fall on the roof of an average home every year, so make sure you collect it.

Use water butts

“When watering the garden use water butts first so there is capacity to collect water in summer downpours,” says Barter. After all, there isn't much point in having a water butt if it's constantly full and overflowing.

Local councils, water companies and DIY stores are often good places to purchase basic affordable plastic water butts. It's also worth looking on local Freecycle and freebies web pages and and Facebook groups as there are often people looking to rehome old water butts. If your butt is going to sit somewhere out of sight, such as an allotment or at the end of the garden, then using unsightly old barrels and wheelie bins is also an option.

Find out how to install a water butt

Plant smartly

Plant plenty of tall vegetation. Hedges and trees catch water on the leaves from which much evaporates before it even reaches the soil, preventing the soil from becoming waterlogged.

After a period of drought the surface of the soil can become hard and baked, making it harder for sudden rainfall to penetrate the ground. This can cause the rain to run downhill and cause flooding. Trees can help dry the soil in areas where the ground becomes saturated because they can gulp up heavy rain, particularly in clay soils where drought can cause fissures that soon fill with water.

Don’t leave bare patches

Avoid leaving bare patches of soil in your garden. Bare soil compacts under heavy rain and run-off occurs, often taking your valuable top soil with it.

If you have an area of garden that you don’t use then instead of leaving it bare cover with mulch or sow with a speedy green manure crop, such as mustard. You could also plant it up with wildflowers and create a little refuge for wildlife.

Find out about green manures

Even patios can collect rain

Don’t want to give your patio up? That’s fine, but it can still help collect water. “Containers, even hanging baskets, absorb water each time it rains,” says Barter. “Covering as much as is convenient of the patio with container plants will go far to reduce run-off.”

Even a few buckets dotted around the patio when you know wet weather is on the way can be useful – simply empty them into water butts, ponds or flower beds once it has passed.

Use porous paving

Paving and tarmac increases the risk of water run-off by about 50% so use porous paving wherever possible. If using gravel, use plastic or concrete reinforcing cell units to keep the gravel in place and spread the load, as seen in the WWT Working Wetland Garden below.

Use your pond as a reservoir

Allow pond levels to fall in dry periods (making sure any fish in the pond still have enough water) so they can fill up again during sudden downpours.

Find out how to create a wildlife-friendly pond

Consider a green roof

A planted or green roof looks great and can also absorb water, and if you can't face the cost or inconvenience of greening the roof of your house outbuildings can be used instead. "Sheds and other small structures are relatively cheap and practical and easier to ‘green roof’ than bigger buildings," explains Barter. What’s more, they look fantastic and are good for wildlife as they provide a source of nectar and a place for insects to hibernate.

Pay attention to the weather forecast

“Monitor weather forecasts and avoid watering before rains,” advises Barter. “Rain won’t soak into saturated soils and is likely to run off, possibly in damaging ways. And you might be able to save a job if the rain is heavy enough to do your watering for you.”

The WWT Working Wetland Garden at RHS Hampton Court Palace Flower Show in 2016

Designed by Peterborough-based garden designer Jeni Cairns, the Working Wetland Garden allows water to run off the roof and through a water feature where plants and soil slow down the water before it ends up in a wildlife-friendly pond. During heavy rainfall the pond overflows into a mini wetland that releases the water slowly.

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