Rain Garden Guide

1
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

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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.

3
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

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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.

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Why are they important?

• Rain is natural stormwater isnt
• 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.

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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
• Dont 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

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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
  doesnt 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.
• Dont excavate an extensive rain garden under
  large trees.

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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

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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.

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Drainage Area

• Determine Drainage Area of the Property

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Determine the depth of the raingarden
12
Shape

• Determine the shape of your rain garden
• Sketch below

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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.

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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.

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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.