Table of Contents

 

What is a rain garden?

A rain garden is a shallow, planted depression in your garden designed to collect, filter, and allow rainwater that runs off hard surfaces (roofs, patios, driveways etc) to soak into the ground rather than overwhelm drainage systems. Rain gardens hold water temporarily – usually draining within 24-48 hours after heavy rain – so it’s not a pond, more of a sponge set into your garden to slow the flow of water. Rain gardens are designed to reduce run-off, prevent surface flooding, and help with water quality whilst providing huge wildlife benefits and just being downright pretty. Want to learn how to build a rain garden? Then this article, put together for you by our team of drainge engineers (who love to provide the very best drainage advice) is the perfect place to start.. Please read on..

how to build a rain garden

Image courtesy of gardendesign.com

 

What are the benefits of a rain garden?

The benefits of a rain garden are many, but here’s a few of the key benefits and advantages of adding a rain garden to your overall household drainage plan.

  • Helps with drainage problems: redirects water away from lawns, flowerbeds, and foundations, reducing soggy patches and erosion.
  • Reduces flood risk: slows down water run-off during storms so local drainage/sewer systems aren’t overwhelmed.
  • Improves water quality: filters out pollutants picked up on hard surfaces.
  • Supports biodiversity: attracts pollinators, birds and other wildlife, especially if you use native, moisture-tolerant plants.
  • Low environmental impact: fewer artificial drainage channels, more natural soil & plant solutions.
  • Aesthetic enhancement: a rain garden can be a stunning landscape feature, adding diversity, colour and interest to your garden.

 

How do I build a rain garden at home?

Rain gardens are not difficult to make until you get to the very large ones, designed for serious surface water issues. However, there are lots of steps to consider and having the right tools will make the whole process a lot easier. Here are the seven key steps to consider, from planning to planting, for a domestic rain garden project:

  1. Choose the right location: Look for low-spots where water naturally moves, but ensure it’s at least 3-4 metres (or about 10ft) from your house foundations to avoid any water ingress risk. Also, avoid underground utilities.
  2. Work out the size and depth: A common rule in the UK is to make the rain garden about 20% of the roof or hard surface area draining into it. Depth usually around 10-20 cm for domestic gardens. In soils that drain very slowly, you may need to go a bit deeper.
  3. Test the soil drainage: Dig a test hole (~30 cm deep), fill with water, see how long it takes to drain. If it drains within 24 hours, that’s good; if much longer, you may need to amend soil (sand, compost) or adjust design.
  4. Excavate and shape: Dig out the area, shape sides gently (so they don’t collapse), flatten the base. Use any soil you remove to build gentle berms (raised edges) if needed, to keep water in. If diverting water from downpipes, you might need channels, or a downpipe diverter.
  5. Improve the soil mix: Mix in sand, compost, and good topsoil to get something free-draining but moisture-retaining. A typical mix might be in the order of ~50-60% sand, 20-30% topsoil, 20-30% compost (depending on what you start with).
  6. Planting: Use native, moisture-tolerant plants in the centre (which will be wettest), and more drought-tolerant species around the edges. Use a mix of grasses, perennials, shrubs for structure, wildlife interest and visual effect. Plant in drifts, not just single plants.
  7. Add mulch & finishing elements: Mulch helps with moisture retention, weed suppression. Use rocks, stones or gravel around inlets to avoid soil being washed away. Edging or a small bund helps contain water. Ensure overflow is accounted for so excess water has somewhere to go without damaging garden or property.

 

Do you want to investigate building a rain garden? Click contact us to request a free quote or speak to a member of our team on: 08082 504 203

 

How much does a rain garden cost to build?

The cost of building a rain garden in a domestic setting in the UK depends on size, soil condition, planting specification, whether you do it yourself or hire professionals, and how complex the water diversion or overflow control needs to be.

DIY Costs

If you do it yourself, costs are significantly lower because you supply the labour – make your own study of the land and manage the project yourself. For a small-to-medium rain garden (say 4-6 m²), prices typically range from £300 to £800. This includes soil amendments, plant stock, mulch, edging, possible downpipe diverter or small channel. Time required would often be a weekend to a few weekends depending on how large, how many plants, and how much preparation is needed (digging, soil testing etc.).

Professional Installation Costs

Hiring a professional ensures proper site assessment, soil testing, correct plant selection, and execution. For a typical small to medium domestic rain garden, professionally installed in the UK, expect to pay around £1,500 to £3,000. For larger plots, complex drainage, or where specialist soils / attenuation or overflow systems are needed, costs can run over £5,000+. Do you want a more definitive price? Contact us on 08082 504 203 and we’ll help provide a cost for a professional drainage team to build and install your rain garden.

Case Study & Local Project Costs

To give you some real UK examples: the Nottingham retrofit rain gardens project (148 m²) came out to about £460 per m² for the full specification, though simpler versions (just filled with aggregate etc.) were nearer £300/m². Also, in West Lothian, a park improvement rain garden cost ~£4,750 including planting, delivery, excavation etc. for a modest sized garden plot.

How Long Does It Take?

For the hard-working DIYer, a small to medium rain garden often can be completed across one to two weekends. That includes site marking, excavation, soil mixing, planting, and initial mulching. If the project is larger, soil is difficult, or water diversion/trenching is involved, expect more time (perhaps several weekends). Professionals will often complete similar small-to-medium jobs in 1-3 days once site prep is done.

Option Estimated Cost (UK) Cost per m² (if relevant) Time Required What’s Included
DIY Rain Garden (Small / Medium, ~4-6 m²) £300 – £800 ≈ £75-£200/m² 1 – 3 weekends Labour by homeowner, soil mixes, plants, mulch, edging, simple water diversion
Professional Installation (Small / Medium) £1,500 – £3,000 ≈ £200-£500/m² (varies with specification) 1 – 3 days Full service: site survey, soil prep, planting, finishing, possibly channels/diverters/overflow
Large / Complex Project £3,000 – £5,000+ ≈ £400-£600+/m² depending on drainage/structure & planting Multiple days up to a week+ May include specialist soils / attenuation, major water diversion, heavy planting, decorative finishes

 

When should I call in a professional to install a rain garden?

  • If your soil is heavy clay and drains poorly.
  • If the garden area is very close to the house foundations (risk of water ingress).
  • If a large surface (roof, driveway) is draining into the garden – design and sizing become more critical.
  • Where there are existing drainage issues: repeated flooding, blocked drains, or water already causing damage.
  • If you want specialist planting, or need to integrate the rain garden with other SuDS (Sustainable Drainage Systems) features, or you require permits or local approvals (depending on location).

 

How do I keep my rain garden healthy?

Once installed, a rain garden doesn’t require constant fuss, but caring for it ensures it works as expected and looks good.

  • Weed regularly in the first year to reduce competition and allow your chosen plants to establish. Remove invasive species.
  • Refresh mulch each spring to retain moisture, suppress weeds, protect soil structure.
  • Water newly planted species during dry spells until they are well established.
  • Keep water inlets, downpipe diverters, rills or channels clear of debris (leaves, litter) so water flows freely.
  • Replace or move plants that are struggling; adjust planting zones if some parts stay too wet or dry.
  • Monitor how the garden drains after heavy rain. If water is staying too long (more than ~48 hours) or pooling, investigate whether soil is compacted or inlet/overflow blocked.

 

Final thoughts

Rain gardens are a smart, effective, and beautiful way to manage surface water run-off at home. They combine practical drainage solutions with benefits for biodiversity, aesthetics, and environmental health. If you’re comfortable with DIY and have good soil, modest size and moderate scope, you can undertake the project yourself. But if any complications exist – poor soil, large catchment, proximity to foundations, or serious drainage problems – PM247’s drainage experts are ready to help. Our professional services can ensure your rain garden is correctly designed, properly constructed, and reliable for years to come.

Don’t hesitate to contact us if you need help with surface water issues or any other drainage problems. Or call PM247 on 08082 504 203 for urgent enquiries.

 

FAQ

Here are some of the most commonly asked questions about rain gardens. Click to expand the answer.

Will a rain garden attract mosquitoes?

No – a well-designed rain garden should drain within 24-48 hours, so standing water doesn’t linger long enough for mosquitoes to breed. If water is standing too long, check whether inlet or outlet is blocked or whether soil is too compacted.

How big should my rain garden be?

A good guideline is to size the rain garden at about 20% of the roof or hard surface area that drains into it. If the catchment area is large, you’ll need a proportionally larger rain garden. Depth around 10-20cm for domestic setups works well, perhaps deeper in slower-draining soils. Consider slope, soil type, and expected rainfall intensity.

When’s the best time of year to build one?

The best time is during drier months – late spring through to early autumn – so soil is workable, plants can get established before winter, and there’s less risk of heavy rain disrupting the work. Avoid building when soil is waterlogged or frozen.

Can I use any plants in a rain garden?

You need plants that tolerate both wet and dry conditions. Native moisture-loving species in the centre, drought-tolerant around the edges. Avoid plants that dislike waterlogging or soggy soil, such as plants or herbs that thrive in the Mediterranean. Also, choose plants with good root structure to help soil aeration and stability.

Does a rain garden require planning permission?

Usually not, for a standard domestic garden rain garden, planning permission isn’t needed. However, if you’re modifying drainage systems significantly, diverting water into public drains, or making substantial land reshaping, local council or building control may need to be consulted. Also check for utilities under the ground. When in doubt, get a professional survey.

What maintenance is required long-term?

After the first year, maintenance reduces. You’ll likely need annual weeding, pruning, mulch refreshing, and checking inlet/outlet channels. Depending on plant species, occasional replacement or trimming of plants will keep things looking good. Monitoring drainage after big storms helps ensure performance remains good.