Rain gardens are becoming more and more important to include with garden and landscape design across the UK, as well as new house building, right from the off-set. The results of climate change mean warmer but wetter weather, so managing excess rainwater and flooding has never been more important or relevant.
Why are rain gardens so important?
A rain garden is one that is designed to spread rain run-off and excess water to reduce pooling in one area and to slow down the movement of rainwater to reduce flash flooding.
Plants are key here, and perform the function of slowing rainfall across the levels of a typical house. Water takes the course of least resistance and plants and their roots are key to creating more resistance.
Ensuring the rainwater is absorbed into the ground instead of into storm drains means it can be cleaned and purified by the soil, as well pollutants being reduced. Plants and trees have multiple, endless benefits for our environment, versus hard surfaces, so it’s easy to see why planted areas are preferable.
It is absolutely our responsibility as garden and landscape designers to design rain garden features into residential, commercial and public spaces. The majority of developers and housebuilders are not forward-thinking and just aren’t designing these features into new build developments.
We work with high-end architects on unique builds in the countryside (also known as Paragraph 55 houses) – and ALWAYS ensure rain garden planting is designed into landscape design from the beginning.
A typical residential house and street has a number of hard impermeable surfaces, including pavements, tarmac driveways and paved over gardens, which do not absorb rainwater. This means excess rainwater runs right across these surfaces and can cause flash flooding.
Greening Grey Britain
The RHS launched a campaign, called Greening Grey Britain, two years ago to educate the environmental and botanical perils of gardens being paved over. The organisation is using the campaign to highlight the benefits of ensuring there are as many planted areas in our residential areas, gardens and towns as possible.
These benefits include protecting us from flooding and extremes of temperature, but also improved air quality, insulation of buildings, more habitat for wildlife, just to name a few.
Our gold award-winning RHS Tatton garden
Rainwater techniques were employed into our gold-award-winning RHS garden called ‘2101’. Although, this show garden in Cheshire was set in the year 2101 to examine the effects of global warming, as garden designers we also use the same rain garden techniques in the gardens we design and landscape today.
In the 2101 garden, we created an upper and a lower level to the garden to channel floodwater and excess rainwater away with drainage channels. On the lower level, we chose plants that can tolerate a lot of water, as well as high temperatures, and planted them very densely so there were plenty of roots to absorb water from the soil.
Here are four easy ways to incorporate DIY rainwater garden techniques at your home
Homeowners can employ a variety of techniques and DIY design solutions to alleviate rainwater run-off and flash flooding on our own properties. Remember that simply having plants in your garden at all is an excellent way of absorbing excess rainwater and reducing flooding.
- Green roof
The inclusion of a green roof is the first place to look when looking to slow the movement of water through your property. A green roof, which is one covered in plants, acts as a barrier against weather, as well as absorbing rainwater.
A green roof also provides insulation and generally protects the roof surface. Moss on an old roof acts in exactly the same way but is obviously less attractive to look at. The easiest way to install a green roof is to start with a shed, but extensions and even new build houses also look fantastic when covered in a green roof.
The book Small green roofs by Nigel Dunnett is an excellent resource and Professor Dunnett is an authority on the subject.
- Green walls
Although on a vertical plane, green wall surfaces also slow the flow of rainwater down vertical surfaces and insulate properties as part of their lasting effect. There is no need to go down an expensive prefab solution here either – low key and lows cost can work well for the DIY-er.
Ivy on a wall surface generally has the same effect as prefab modules and is much less liable to need regular maintenance. Although, we would recommend that ivy be grown on a frame slightly away from the brick surface. This has two effects in that it prevents damage to brick work and also allow nesting birds to get behind the structure for nesting purposes.
Our native ivy Hedera helix is also a fantastic source of pollen late in the year for bees and other insects when ‘last orders’ has been called on the other plants in the garden.
Most people utilising these techniques on outside walls of their property will generally see a reduction in energy consumption as plants cause buildings to retain warmth in winter and keep them cool in summer particularly in urban environments.
- Down spout water features
Creating a water feature around your downspout, which funnels water down your gutters and into the drainage system, is a fantastic way to utilise rainwater run-off in an environmentally-friendly way.
We would recommend creating a sump at the bottom of the downspout that collects water, and this offers gardeners the chance to get creative with planting and features. Using aquatic marginal plants with substantial rootballs will absorb standing water and allow water to evaporate into the atmosphere. Equisetum hymale is especially attractive in this location.
We have previously created infinity water features which collect water from the down spout and used aquatic grasses and perennials plants to create and extra dimension in small urban front gardens that are also attractive to wildlife
- Open ground water courses
Where space allows, water courses can be situated in among wider planting schemes and can be particularly attractive when designed as dry riverbed, with rocks and pebbles. This must be situated in the lowest part of the garden to allow them to be effective and collect surface runoff.
A man-made pond area for holding and slowing water in prolonged wet spells and then drying out in prolonged dry spells, can be very attractive in a residential garden. Rather than a pond or a water feature, these water courses mimic a natural wet area, which may be wet during the winter, and dry out during the summer.
We would recommend this should be planted with marginal water plants, which allow a natural evaporation of water and their ability to withstand prolonged periods of wet and dry weather.
What are the best plants to use in a rain garden?
It’s important to choose resilient native plants (where possible) that can handle being inundated with water, as well as spells of dry warm weather. This is because a rain garden is designed to absorb and distribute a flow of rainwater, and not to hold onto water.
Here are some of the plants we chose for our 2101 garden with future temperatures increases in mind, but that will also be very happy in our current climate. You can view the full RHS Tatton ‘2101’ planting list for more ideas.
- Sanguisorba “Tanna”
This beautiful tall flowering plant with a small flower does well in moist soil, but also does not suffer in dry soil. In general, they are undemanding plants and can be divided in the autumn. Pictured above.
- Sedum “Purple emperor”
Surprisingly, this succulent is extremely versatile and is at home in harsh drought conditions is it is in wet marginal conditions (unlike many other succulents). With deep purple flowers and a dark plum, almost black foliage, this sedum holds water in its fleshy leaves so also does well during a drought. It’s a very easy plant to grow, needs very little interference, and can be split in the spring, after its growing season has ended.
- Hosta “Sum and Substance”
Hostas are clump-forming herbaceous perennials, which are selected for their attractive foliage, just as much as their flowers. In early summer it produces pale lilac bell-shaped flowers.
These are a hardy plant tolerating a variety of soils and conditions, however, they are a choice meal for slugs, which gives a paper snowflake-effect to the leaves if the slimy pests are not diverted elsewhere.
- Carex morrowii “Ice dance”
This is a gorgeous grass, which creates a fantastic textural look when interspersed with flowering plants. This is a really easy plant to care for, doesn’t spread too quickly and can handle different conditions.
- Primula vialii (also known as Chinese pagoda primrose)
This stunning Primula has a poker-shaped flower at the top of a tall stem with purple at the bottom and a red-pointed tip. In terms of a rain garden, this plant does well in a moist and poorly-drained environment. It also prefers partial shade, so do take this into account if your garden is in full-sun for much of the day.