Rain Gardens

• Build your rain garden next to a drainage area, where rainwater will feed into it from downspouts, driveways or low points in your yard.
• Look for a space that is relatively flat. Installation of the rain garden will be much easier!
• Rain gardens should not be within 15 meters (50 feet) of any steep slopes on or around your property.
• Before doing any digging for this project, you must ensure all underground utilities are located and marked.
• Be sure that the area you select gets full to partial sun.

The size of a rain garden is based on the amount of water it needs to hold before it overflows at the exit point. The amount of water flowing into the garden depends on:

• The size of your roof and other hard surfaces that will be draining into the garden
• The distance and slope (grade) between the garden and the house

For example, a rain garden close to the house, collecting water from a large roof, paved driveway, and sloped lot, would need to be bigger than one that is further from the house, collecting water from a small roof, with no paved surface and minimal slope.

In general, rain gardens on residential properties range from 10 to 30 square metres (100 to 300 square feet). Soil type and drainage rates can also affect size (see section below). Online tools and calculators are available to help determine the right size for your property.

Remember, if needed you can also build multiple rain gardens or build a smaller one and plan for it to overflow more often.

The shape of the rain garden will be determined by how much space is available and how large a rain garden you want. An organic shape that moves and flows with the land looks nice and allows the rain garden to do its job better.

• Try integrating the rain garden into the rest of the landscape.
• Consider curved lines rather than straight lines.
• A rain garden can be as formal or as wild as you like; pay attention to how it blends with other design features of your home.
• A rain garden doesn’t have to be separate from other plantings. Consider making a depression within a perennial bed or shrub border (especially if space is tight and you don’t have room for a larger rain garden that stands alone).

Rain gardens should capture runoff and allow it to percolate into the ground below. If your soil is mostly clay, it may not be able to filter the water quickly enough, resulting in overflow. Depending on the type of soil in your yard, you may need to amend it with other soil types to create a functional garden.

1. Test soil and drainage for suitability

• Option 1 – Dig a 15 cm (6 inches) deep hole where you plan to dig your rain garden and fill it with water. If the water soaks up in less than 24 hours, the soil is suitable.
• Option 2 – Take a handful of soil and dampen it with water; kneed the soil and squeeze it into a ball. If the ball remains, work the soil between your forefinger and thumb, squeezing it upward to create a ribbon of uniform thickness. If you can create a ribbon 2.5 cm (1 inch) long or longer before it breaks, the soil is not suitable (i.e. clay content is too high) and would require amendments. The soil should also feel gritty rather than smooth.

2. Amending your soil

Rain garden soil usually contains a combination of compost and sand to allow water to infiltrate quickly through the soil. If you need to amend your soil, considering the following ratios:

• If you have clay soil, use approximately 60% sand and 40% compost
• If you have sand or loam, use 60% existing soil, 40% compost

1. Locate underground utilities on your property by contacting Ontario One Call or call 1-800-400-2255

2. Mark out your rain garden to make sure you’re happy with the size, shape, and location

• Use spray paint or string tied on wooden stakes
• Mark the location of water inlet and outlets (if you have a place for overflow water to travel)

3. Dig your garden

• Your new garden should be about 85 cm to 100 cm (~3 feet) deep, but may differ depending on its size and the amount of water draining to it.
• Try not to compact the soil while you’re digging

4. Fill your garden

• Fill the dug garden using the amended soil described above (a mixture of sand, compost and existing soil) to a depth of 60 cm (2 feet), leaving approximately 25 cm (10 inches) for plants, mulch and water pooling. Rain gardens should be sunken to allow rain water to collect and filter into the ground.
• Lightly tamp soil down every 20 cm (8 inches)

5. Create a berm

• Use any remaining soil to create a berm on the downhill edge of the garden, to prevent water from flowing across the surface of your garden

6. Create an inlet

Rain gardens require a source of water. Some options include:

• Extending a downspout to the garden
• Overflow pipe from a rain barrel
• Infiltration trench lined with plants or decorative rocks

Placing a few small stones at the inlet (where the water enters the rain garden) will slow the flow of water and protect soil from eroding.

7. Create an outlet

Most of the year, water that flows into the rain garden will soak into the ground; however, during more intense storms or when the ground is already wet, the garden may fill up and overflow.

When creating an outlet, consider:

• Locating it on the downhill side of the garden
• Directing excess water to a second garden or an open area of lawn
• Placing small stones at the outlet to slow water and prevent erosion

According to Ontario’s Excess Soil regulation, if you have more than 100 m³ (130 cubic yards) of soil – more than 10 dump trucks worth – you need to consult the Ontario.ca website for more information.

Most residential rain gardens will produce less than 100 m³ (130 cubic yards) of excess soil. There are several options for repurposing the excess soil, such as:

• Creating a berm for the rain garden
• Reusing the soil for planting beds and pots
• Spreading it throughout the garden and lawns
• Re-grading areas of your property
  • Note – if you are using the soil to regrade your property, contact Grading at City of Richmond Hill
• Renting a bin from a local landscaping company to collect and take away the clean fill 

You can use the resources below to help you find the right plants for your rain garden:

• Network of Nature Native Plant Database  – is a native plant data base for all of Canada, and you can create lists based on where you’re located, soil type, amount of sunlight, plant types, etc.
• Network of Nature Find a Nursery – helps you find where you can buy these plants near where you live
• For a list of some common native plants found in Richmond Hill, check out the City’s Native Wildflowers Selection Guide

Well-designed rain gardens should require minimal maintenance, aside from general upkeep. Some maintenance considerations include:

• Mulching – check mulch annually and add fresh mulch to maintain even coverage
• Erosion and debris – with flowing water, some erosion may occur; check the garden a few times a year to identify any maintenance needs, and remove any debris from the inlet and outlet
• Fertilizing – most rain gardens will not require fertilizer as native plants are often well suited to existing conditions
• Weeding – only required as needed, based on your desire for aesthetics, or if a change in function is observed within the garden
• Watering – your rain garden should be watered infrequently but thoroughly, especially during prolonged droughts. Remember, you don’t want to over water your plants.

1. Will rain gardens attract breeding mosquitoes to my property?

No. Mosquitos need standing water (like a small still pond or marsh) to lay and hatch eggs. A properly constructed rain garden will drain within 48 hours, often faster – so the water will not be sitting long enough for mosquitos to breed.

2. Are rain gardens difficult to maintain?

If your rain garden was designed and installed properly, it should not require much maintenance, especially if native plants were used. The maintenance needs are similar to other gardens. The main difference: you need to ensure your rain garden is functioning as intended. This means:

• keeping the inlet and outlet clear of debris that might affect the flow of water  
• checking the garden after a rainfall to ensure it is draining appropriately

3. Will a rain garden form a pond?

If properly designed, a rain garden will not form a pond during or after a typical rain event. In fact, by capturing and filtering runoff from your property, a rain garden may prevent ponding that would otherwise occur.

4. Do rain gardens comply with Richmond Hill’s property standards?

The City’s Grass and Weeds By-law permits wildflowers, ornamental grasses, etc. that exceed the by-law’s maximum height of 20 cm (8 inches), as long as the plants are contained within a clearly defined garden. 

5. What if I cannot do the installation work myself?

The following links provide tools and guides for finding and selecting contractors who can help create a rain garden on your property:

• Find a Certified Installer - Green Communities Canada
• Landscape Ontario guide to selecting a contractor
• OALA guide for landscape architects (including retaining a contractor)
• YR Fusion Landscaping

6. How much does it cost to install a rain garden?

Costs can vary greatly depending on the size and style of your project, the existing condition of your lot, the plants used in the garden, the equipment needed, and the use of contractors. A small DIY rain garden will likely cost around the same as any other garden.

Richmond Hill residents can purchase native plants at a subsidized rate through the City’s Healthy Yards program and through Local Enhancement & Appreciation of Forests (LEAF).  

I have installed a rain garden on my property.  What should I do if…

1. Plants are dying?

• Water according to plant type:  some plants require more watering than others. Too little or too much water can affect the health of your plants.
• Consider how much sun/shade your plants are receiving. Some plants may suffer if they are exposed to full sun throughout the day, while others thrive with plenty of direct sunshine.
• Ensure your garden is draining properly. Too much water in the soil can affect plant health.
• Check your soil composition. Some plants will struggle if your garden has a high clay or sand content. You may need to amend your soil with compost.
• Check for signs of disease or pests.

2. Water is pooling in and around the rain garden?

• Ensure there is a clear outlet for water to flow out of the rain garden when needed
• Consider your soil type:  if you have very high concentrations of clay, water will not be able to drain quickly enough.  You may need to amend the soil to decrease the percentage of clay.
• Divert some of the runoff water (e.g. from the downspout) away from your rain garden’s inlet

3. I need professional advice or assistance?

The following links provide tools and guides for finding and selecting contractors with rain garden expertise:

• Find a Certified Installer - Green Communities Canada
• Landscape Ontario guide to selecting a contractor
• OALA guide for landscape architects (including retaining a contractor)

1. Examples and Case Studies

• Windfall Centre – case study of a residential rain garden (in photos)
• Green Communities Canada – Ontario rain garden examples
• TRCA STEP Case Study – Town of Ajax Rain Garden Retrofit
• Town of Ajax Rain Garden Monitoring Report

2. Guidebooks and Toolkits

• TRCA Complete Guide… (LINK)
• Green Communities Canada – RAIN Toolkit
• Landscape Ontario rain garden video series
• Essex Region Conservation Authority – How to Create a Rain Garden: A Guide for Homeowners! (includes FAQ)
• Massachusetts Rain Garden Guide – includes technical specifications for sizing

3. Related information

• York Region Fusion Gardening – tips and links, including link to certified contractors