Arranging a rain garden step by step - it's easy!

On hot summer days we will appreciate them for lowering the ambient temperature and serving as a water reservoir for plants growing in our gardens, which will save us time and money on watering. For more reasons to start a rain garden, click here. In the meantime, let's get to work and...

... make a garden!

People who do not like spending hours going through specialist gardening guides and magazines or who do not have much time will be pleased to know that the design and construction of a rain garden is not a particularly complicated task and its use requires practically no commitment. However, it is still worth making a few preparations before getting down to work:

Let's calculate the optimal garden area

The principal function of a rain garden is to collect rainwater. Therefore, to know its optimum size, we need to know how much water it should take in. How to calculate this? In home rain gardens most of the rainwater comes from the roofs. Let's first count the surface area of the roof. The size of the garden should be about 2% of this surface and so e.g. 50 m2 of the roof equals 1m2 of the area which should be allocated for our garden.

Check the type of soil.

In case of soil it may be helpful to have soil tests done before starting any investment. If we do not have them, the type of soil can be determined by a landscape architect, geologist or sanitary designer. With this knowledge we can determine what type of rain garden we can build on our land. There are three options to choose from: a 'wet' garden, a 'dry' garden and a container garden.

Impermeable or poorly permeable ground:

A 'wet' rain garden

A characteristic feature of a "wet" garden is a sealed bottom (lined with a sealing material such as PVC foil) - that is, the water that collects in it does not soak into the ground. Therefore, the element which we must necessarily remember about is the so-called emergency overflow, which makes it possible to discharge the excess of collected water to the sewage system. This will prevent overflowing. An advantage of this type of garden is that it can be located close to the building. The distance between the garden and the walls of the building depends on the depth of the foundations (the minimum distance is 30 cm when the foundations are at least 65 cm deep).

Rain garden in a container

Choose this solution if your backyard garden is not the largest. Finding space for a small container is often possible even in pre-arranged space. You can also easily place it on stone tiles or a concrete path. Despite their small size, container rain gardens achieve a retention function similar to that of in-ground gardens! The garden is placed underneath a suitably sized gutter outlet, but not closer than 30 cm from the building wall. As with a 'wet' garden, we need to ensure that excess collected water drains away, e.g. into an absorption well or inspection chamber.

Permeable ground:

A "dry" rain garden If, after rain, the water on our plot soaks into the ground within a short time then a "dry" (infiltration) rain garden. For the arrangement choose a place at least 5m away from the walls of nearby buildings. This will protect the foundations from damp. Because water soaks into the ground efficiently, 'dry' rain gardens usually do not require the installation of drainage pipes and an emergency overflow. The type of garden will also influence the choice of vegetation and the type of work we need to do.

Prepare the necessary materials

A rain garden will require us to lay several layers of earth and aggregate, which we should prepare in advance. To create the layers we need

washed gravel (2-8mm diameter) - drainage layer (20cm thick)
washed sand - filtration layer (10 cm thick)
fertile soil (garden soil mixed with sand in ratio 1:3 - one part soil to three parts sand) - vegetation layer (30-40 cm thick)
flat, large stones and washed gravel (up to 16 mm in diameter) - anti-erosion layer (3-6 cm thick)

To make a garden with a sealed bottom ('wet' and 'container' garden) you will additionally need: PVC film, PVC tape, pipes (90 mm in diameter), a cover, connectors and an openwork grate. If we are going to arrange the garden in a container, let's prepare additionally a chosen container (e.g. boxes or pots). The container should be 1m high and be able to withstand the pressure of the soil. The colour and material it's made of depends entirely on your tastes, as does the shape. Only long and narrow containers won't work.

We choose the plants.

For a rain garden, choose native, preferably perennial species that occur naturally in coastal areas of rivers, lakes and ponds, as well as boggy areas. Hydrophytic plants are resistant to periodic flooding and drought, and their rhizomes and roots capture and break down harmful substances. It is recommended that they make up about 70% of all plants growing in our rain garden and a minimum of 50%. For rain gardens, we recommend: purple loosestrife, valerian root, marsh,  moneywort, carex sylvatica,  spotted loosestrife, common comfrey, dusky crane's-bill and water mint.

Rain gardens are associated with low plantings and grassy vegetation. If you have a larger garden, there is nothing to stop you from planting trees and shrubs. As with perennials, choose species which can be found in nature by bodies of standing water or flowing watercourses. These can include, for example, black alder, white willow, wild cherry, grey willow, lava willow, purple willow, white dogwood and coral callas.

As time goes by, the plants in your garden will grow. Make sure you have enough space to give them the right conditions for this. Also remember to choose plants which suit the type of garden.

9 easy steps to your own rain garden:

Here we suggest how to easily turn theory into practice and make your own "wet" rain garden, which is considered by many to be the most difficult to do.

Step 1 Determine the optimum distance between the garden and the walls of buildings. When choosing the location of the basin (i.e. hollow in the ground), in which our garden will be created, make sure that there are no trees with extensive root systems growing nearby and there are no underground infrastructure devices such as cables and pipes.

Step 2 Seal the 80-90 cm deep basin (the larger the garden, the deeper the basin) for the entire garden with a layer of PVC foil (or other impermeable material). Lay it so that the individual sheets overlap by approx. 20 cm and then connect them with PVC tape

Step 3 Lay a 5 cm layer of gravel on top of the soil and place the drainage pipe horizontally, at a slight angle.

Step 4 Close one end of the drainage pipe with a cover, and connect the other end directly to the rainwater drain (you may need the help of a plumber) - this will be our emergency overflow, which will allow the drainage of excess water.

Step 5 Install a 3-connector to the drainage pipe and then vertically, at a right angle, install the so-called overflow pipe (it should protrude 10 cm above ground level in the garden). Close the end with an openwork grate to prevent leaves and other debris from falling in.

Step 6 Lay out the layers in order: drainage (gravel), filtration (sand), vegetation (fertile soil mixed with sand).

Step 7 Plant the plants in the vegetation layer.

Step 8 Finally, line the garden with several large, flat stones and sprinkle fine gravel in between to create an erosion control layer that prevents the soil from washing away.

Done!

Caring for the  rain garden

Rain gardens do not require any special care. With the exception of long periods of drought, they can do without watering. You can also forget about fertiliser for good.
Garden work is limited to removing dead plants and replenishing planting. Once a year, preferably in early spring, take the time to mow and trim dead plants and if necessary desludge the bottom to the originally designed level. You can avoid desludging by regularly checking the condition of the flowing elements (pipes, drains) and outlets and inlets (if the garden is equipped with them). You can also place a fleece on the drain to prevent siltation.

The ideal system

A rain garden is a solution, which even with a limited area and a small investment of time and money will allow us to create an aesthetic space, beneficial for the environment, health and even our wallet.