Rain Garden - DIY

Creating a rain garden is a great way to improve drainage on your property, support local ecosystems, and at the same time enhance the aesthetic value of your land. A rain garden helps capture and filter rainwater, thereby reducing runoff and pollution of watercourses.

One manifestation of climate change in our region is prolonged summer drought alternating with torrential rain and thunderstorms. In built-up areas full of paved surfaces, precipitation has no chance to soak into the soil, frequently resulting in ruined crops or the threat of flooding. In addition, water from roofs and paved surfaces is drained away through the sewage system elsewhere, leading to unnecessary landscape drying and a subsequent deficit of water reserves in the soil. A simple and aesthetically pleasing solution is the construction of a rain garden, which naturally slows down stormwater runoff, captures rainwater, and allows it to soak into the soil directly on your property.

What is a rain garden?

A rain garden is a spot in the garden designed to capture rainwater runoff from roofs, driveways, or yards and allow it to soak into the ground. Rain gardens are typically planted with shrubs and perennials and can become colorful, landscaped features in your yard.

Guide to building your own rain garden

This guide will help you create a rain garden on your property. The size and shape of your garden will depend on several factors, such as the size of your yard and the budget you wish to invest. Remember that your rain garden should be neither too large nor too small, but proportionate to the volume of rainwater you want to retain on your property from your roofs and paved surfaces. A rain garden can become a wonderful highlight of your property, offering a lovely place to relax while protecting the quality of local water resources and helping prevent flooding.

Why do we need rain gardens?

The benefits of rain gardens are numerous. They are capable of performing the following functions:

Help mitigate flooding issues
Improve water quality in local streams by filtering rainwater through the soil before it enters a waterway
Enhance the visual appeal of landscape architecture in towns and villages
Replenish groundwater reserves
Increase air humidity and evaporation, acting as natural climate conditioners for towns and villages
Provide and create a suitable habitat for birds, butterflies, and other beneficial insects
Save money on stormwater drainage fees

The most suitable location for a rain garden?

Before the actual installation, it is advisable to: thoroughly map out the terrain, know the surface area from which you are capturing runoff, assess the characteristics of the plot and landscape, and consider future use. A rain garden can be located on a lawn near your house, collecting rainwater from the roof and other paved surfaces on your property. Observe how rainwater drains across your property. The largest sources of runoff are roofs, paved surfaces, and compacted soils.

The distance of the rain garden from your house and neighbors' properties should not be less than 10 meters to prevent water seepage under building foundations. We do not recommend placing the garden where groundwater levels are high, where there is a risk of landslides, or where soil infiltration is insufficient (clay soils). The best location for a rain garden is a sunny spot integrated into the overall garden design, preferably away from large trees or areas with extensive root systems. We suggest locating the rain garden where natural terrain depressions already exist and where runoff water can be easily directed.

Planning

Choose a suitable spot: Ideally, locate the rain garden at least 3 meters away from the house to avoid moisture issues. You should also consider where the water naturally flows.
Size: The size of your rain garden should be based on the size of the catchment area (such as the roof of the house) and the soil type. Generally, a rain garden should be about 20-30% of the drainage area.
Consider soil type: Soil type affects water infiltration rates. Sandy soils have faster infiltration than clay soils. You may need to add soil amendments, such as sand or compost, to improve permeability.

Rain Garden Size

The ideal goal is to create a rain garden that will absorb all captured rain that would normally run off your property. Typically, a standard rain garden for a single-family home ranges from 10 to 30 m2. The size of your rain garden will depend on the following factors:

Depth of the garden
Volume of rainwater runoff from the roof and paved areas
Soil type in your garden

Depth and Slope of Rain Garden Sides

The size of the rain garden will influence its depth as well as the slope of its sides. The ideal depth for a rain garden is between 15 and 30 cm. At a depth of 15 cm, the rain garden will need to be relatively large to provide sufficient capacity for accumulating the captured rainwater volume. On the other hand, a rain garden deeper than 30 cm may retain standing water for too long depending on the soil substrate. We recommend keeping side slopes under 12%. Rain barrels can also be used to collect roof runoff for subsequent discharge into the rain garden; using rain barrels will also impact the required surface area of the rain garden.

Determining the Rain Garden Catchment Area

Calculate the roof surface area of the buildings on your property along with the area of paved driveways and walkways. Designing depth zoning for the rain garden and calculating the catchment runoff area entering the garden is the next step in determining its overall footprint. Depending on your property's topography, you can also design 2–3 rain gardens distributed across suitable areas.

Rain Garden Shape

One key principle is that the rain garden should blend aesthetically and harmoniously into the landscape. The longer dimension of the garden should be perpendicular to the incoming water flow to maximize the garden's water catchment capacity. It should be wide enough for the water to spread evenly. A reliable rule of thumb is to maintain a length-to-width ratio of approximately 2:1.

Design

Choose plants: Focus on native or resilient plants that are well-adapted to local conditions and can tolerate both temporary flooding and dry spells.
Design the layout: Place taller plants in the center or at the back of the garden, and lower plants closer to the edges. Include a variety of species to promote biodiversity.

Site Preparation

Mark the area:** Use lime, marking paint, or garden stakes to outline the shape of your rain garden.
Remove turf and weeds:** Clear away existing vegetation in the area designated for the rain garden.
Excavate the area:** The depth and shape of your rain garden depend on your soil type and overall design. Typically, a shallow depression 15–30 cm deep is sufficient.

Building the Rain Garden

Start by marking out the perimeter of your garden using stakes, flags, or a garden hose laid along the boundary. Once the perimeter is defined, you can begin digging. First, strip the turf/sod. If you are working on level ground, excavate the rain garden bed and transport the excess soil to another location in the garden where it can be utilized. If the site is sloped, use the excavated soil to build up a berm on the downhill side. Compact and level the berm. Continue digging down to the required depth and, if needed, raise the berm further, compacting it and then covering it with turf/sod.

You can dig the rain garden by hand or using a mini-excavator. CAUTION! Avoid operating an excavator directly within the excavated rain garden bed to prevent soil compaction.

Planting and Setup

Add soil amendments: If necessary, mix in compost or sand to enhance drainage.
Plant: Plant the selected varieties according to your design layout. Water thoroughly immediately after planting.
Mulch: Apply a layer of mulch around the plants to help retain soil moisture, suppress weed growth, and give the garden a tidy finish.

Maintenance

Water the plants: Water regularly until plants are fully established, especially during dry periods.
Inspect and clean: Regularly check the garden to ensure water is infiltrating properly and is not blocked by debris or sediment.
Prune and clear dead growth: At the end of the growing season, remove dead plant material to encourage healthy new growth in the spring.