Rain Garden Guide

• What is a rain garden?• History• Stormwater• Why are they important?• Rain Garden Basics

– Location– Size– Determine soil type– Determine the drainage area of your

property– Determine the depth of the raingarden– Determine Shape– Types of Plants

• Building Your Garden• Monitoring Garden

What is a rain garden?

• A rain garden is an attractive landscaping feature planted with perennial native plants.

• It is a bowl-shaped garden, designed to absorb stormwater run-off from surfaces such as roofs and parking lots.

History

• Rain gardens are a relatively new concept

• They emerged in 1993 in Maryland out of the need for low cost stormwater infiltration methods that would improve water quality

• The idea of bioretention or holding and filtering stormwater in plant systems came about

• The term was later refined as rain gardens as it was more attractive

• Since then, the concept of rain gardens has been developed by other states especially Minnesota, Michigan and Wisconsin

• A more widespread use of such gardens could dramatically improve water quality everywhere

Stormwater

• What is stormwater?Stormwater is the rainfall or snowmelt that flows over our yards, streets, parking lots, and buildings and either enters the storm drain system or runs directly into a lake or stream.

• What is a storm drain?Storm drains are the openings you see along curbs and in streets and parking lots. They carry away rainwater and snowmelt and transport it through the system to nearby lakes and streams. Water and other debris that enter storm drains do not go to a treatment facility.

• What is a sanitary sewer?A sanitary sewer takes household water and waste from toilets, sinks and showers, and transports it to a wastewater treatment facility. There, the water is treated and then discharged back to a lake or stream.

How does stormwater get polluted?As stormwater flows over our lawns and driveways, it picks up fertilizers, oil, chemicals, grass clippings, litter, pet waste, and anything else in its path. The storm drain system then transports these pollutants, now in the water, to local lakes and streams. Anything that goes into a storm drain eventually ends up in a lake or stream.

Why are they important?

• Rain is natural; stormwater isn’t• 70% of the pollution in our streams, rivers

and lakes is carried there by stormwater • The conversion of land from forests,

grassland and agricultural land to urban and suburban lots has reduced the natural ability rain water to infiltrate into the ground because of increased impervious surfaces

• This results in stormwater runoff that carries pollutants from streets, parking lots and lawns into our local lakes and streams, degrading their water quality

• These bowl-shaped gardens trap and remove the oil and chemicals from

stormwater.

Location– Your rain garden should be at least 10

feet away from your house– It can be placed close to your

downspout so it only receives water from the roof

– Or further away so it catches water from your roof and your lawn

– Don’t put it where water already ponds – the idea is to encourage infiltration

– Plants will grow easier in full sun than in shade or under a tree

– A flat area of the yard will be easier to dig than on a slope

Things to avoid when choosing a location

• Avoid creating a rain garden too close to building foundations; this may lead to a leaky basement

• Be aware of rights of way and underground service lines or utilities.

• Re-directing the rain--there are a number of creative and attractive solutions if the rain doesn’t flow naturally to your chosen spot.

• If your land slopes, you can create a flat area for your rain garden in several ways.

• Black walnut trees growing by the garden may spell trouble, due to juglone, a chemical exuded from their roots.

• Don’t excavate an extensive rain garden under large trees.

Size

– You should choose a garden size that you can manage; typical sizes are between 100 and 300 sq.ft.

– The depth can vary between 4 and 8 inches

– A garden that is too small and too shallow will not have enough plant variety and will not provide appropriate infiltration

– Similarly a garden that is too large and too deep will be hard to maintain, expensive and will resemble a hole in the ground filled with water

Soil Type

• Determine soil type• The soaking test

– Dig a hole 8 inches wide and 8 inches deep.

– Pour a bucket of water into it and see how long it takes to sink in.

• The water needs to go down an inch per hour.

– If it takes longer than that, you will need to do additional site preparation to improve infiltration. 

• The ribbon test– To determine whether you have clay soil,

wet a handful and knead it until it is uniformly wet. Squeeze the mud between thumb and forefinger, forming a ribbon. If you can make a ribbon more than 2” in length, your soil is clay.   You may also simply dig a test hole as deep as you plan to dig your raingarden, fill it with water, and monitor how long it takes to dry out.   This will give you a rough idea of your water retention time. It is important to note that clay soil liner that is exposed to the air may shrink and crack, allowing future rain to literally “slip between the cracks” if your pond dries completely.

Drainage Area

• Determine Drainage Area of the Property

Determine the depth of the raingarden

Shape

• Determine the shape of your rain garden

• Sketch below

Plants

• When choosing native plants for the garden, it is important to consider the height of each plant, bloom time, bloom color and its overall texture. Use plants that bloom at different times to create a long flowering season. Mix heights, shapes and textures to give the garden depth and dimension. This will keep the garden looking interesting even when few flowers are in bloom.

• When laying out plants, randomly clump individual species in groups of 3 to 7 plants to provide a bolder statement of color. Use odd numbers when determining how many to plant in a mass. Make sure to repeat these individual groupings to create repetition and cohesion in a planting.

• Try incorporating a diverse mixture of sedges, rushes and grasses with your flowering species. This creates necessary root competition that will allow plants to follow their normal growth patterns and not outgrow or out-compete other species. In natural areas, a diversity of plant types not only adds beauty but also creates a thick underground root matrix that keeps the entire plant community in balance. Once the rain garden has matured and your plants have established a deep, thick root system, there will be lass change in species location from year to year and weeds will naturally decline.

• Finally, consider enhancing the garden by using local stone, ornamental fencing, garden benches or additional flower plantings. This will help give the new garden an intentional and cohesive look and provide a feeling of neatness that the neighbors will appreciate.

Building Your Raingarden

• Your raingarden shall be constructed so that there is 3 differently vegetated sections– a control section in which no vegetation is

grown and mulch covers the depression – a section of turf grass to model the conditions

found at a typical lawn or urban park – section planted with plugs of native grasses

and wild flowers to represent natural conditions.

• Each section shall be equal in area, depth, and soil conditions to the greatest extent possible. The runoff directed to the raingarden will be equally partitioned through use of a manifold.

Monitoring your Garden

• Once the garden has established itself

• Monitor the water quality and infiltration parameters in the raingarden.

• Look at the following: – Inflow– Soil moisture– pH– Nitrate– Phosphorous– Saline– Temperature– Dissolved oxygen– Retention time.