How To Create A Rain Garden

Ahhh. Hear the pitter-patter of little raindrops on the roof and window panes. What a relief. But sometimes it becomes a torrent and puddles around the door. Eventually it flows down the street. Maybe not so good.

Much of the runoff doesn’t stay where it belongs – in the soil. It can damage your home by collecting around the foundation, undermining it, or flooding the basement. It can create a problem for the environment by washing pollutants into nearby lakes, rivers and watersheds. The rapid flow of water can contribute to flooding downhill. Perhaps it’s time to act. A rain garden might be your best solution.

What, exactly, is a rain garden?

A rain garden is a good-sized depression in the soil that’s created on sloping ground to catch the water as it flows and hold it, allowing it to soak into the soil.  It’s planted with different plant species – often native – that thrive in the various conditions created by the garden. The plants hold soil in place and  preventing erosion. Their roots absorb water, as well. Pollutants may be neutralized or dissipated.

What size and shape is a rain garden?

The size of your rain garden depends on your landscape and what it will accommodate. It should cover at least 100 sq. feet – best if it’s larger. But if there’s not enough room for that, a smaller one will do; it’s better than nothing.

The depth also depends upon your conditions. It shouldn’t be deep enough to form a perpetual pond, but not so shallow that water flows in and out in a flash – flood, that is. About 4 inches to 10 inches deep should be about right.

Abrupt angles are difficult to maintain, and not particularly appealing. A simple kidney-shape or something similar with gentle curves is desirable and popular.

Where should I create my rain garden?

The best place to create your rain garden is in the path of the downward water flow. You can learn this by observation. There are other situations to consider, too, like foot traffic. It’s best to avoid places where someone might step into it, trip and fall.

Make sure you don’t site it where you’ll encounter utilities, underground cables, or a septic drain field as you dig. More about that next.

How do I create my rain garden?

Call 811 – the national call-before-you-dig phone number. As their website states, “Anyone who plans to dig should call 811 or go to their state 811 center's website before digging to request that the approximate location of buried utilities be marked with paint or flags so that you don't unintentionally dig into an underground utility line.” Then wait for their people to show up. Be patient. Even when the lines are supposedly marked, dig with caution. Cable television lines, especially, are notoriously shallow.

Mark the chosen site in the desired shape. Lay out a flexible garden hose around the garden’s perimeter. It’s temporary, and can be moved about until you’re satisfied with the shape. You may also mark the area with flags or orange spray paint.

Cut the grass short, then remove the sod inside the perimeter with a spade. Better still, rent a sod-cutting machine. Recycle the sod to cover bare spots elsewhere in your lawn.

Dig to the desired depth with gently sloping sides. The deepest level should be near the lower end with a flat base about 24 inches or more across. This will provide a place for some plants to grow, and allow water to percolate downward evenly.

Test the soil pH. You can obtain a soil sample bag from your nearest Cooperative Extension Service office. Follow instructions. Return the sample to the office, and pay a nominal fee. You should receive the results in a couple of weeks.

Amend the site, if necessary. You might need to adjust the pH according to the soil test recommendations.

Test the water absorption rate. Add a few measured inches of water to the site. If the soil is packed hard so that water doesn’t infiltrate quickly – about ½ inch per hour – you’ll need to break through the hardpan using a method called “double-digging.” You might need to add sand, milled sphagnum or compost – mixing well – to enhance the “structure” making it suitable for plant growth, and to improve the “permeability” of your native soil.

Divide your rain garden into zones, and select plants appropriate to each. Depending on the size of the garden, you might choose plants ranging in size from low ground covers to perennials, small or even large shrubs.

    • Zone 1 is the deepest where water will stand the longest. Plants for this area should be able to thrive in standing water for awhile.
    • Zone 2 is an intermediate area where water will stand for short periods, but drain away. It is just above and wraps around Zone 1. Plants for this area should be able to grow in wet or dry ground.
    • Zone 3 is the uppermost, wrapping around the other two, and will be the driest. Plants for this area should be able to withstand periods of dry weather.

Install your plants according to best practices appropriate to each species. Helpful information should be available on plant labels, from garden center staff, books, magazine and online sources such as our GoGardenNow plant catalog, and here at GoGardenNow – The Gardening Blog.

Mulch will not be necessary. Rainwater will be flowing down into the rain garden, and will wash the mulch right along with it making quite a mess. Lawn grass or ground cover perennials should stabilize the slopes around the edges quite well.

Maintain your garden during the early stages with adequate irrigation. This will help your plants to become established and get a good start. Fertilizer may not be needed, especially if compost was incorporated into the soil during site preparation.

Final thought

Enjoy your rain garden knowing that it will help prevent water runoff damage to your home, landscape and even distant watersheds. In addition, it will add interest and value to your property.