Rain Gardens vs. Swales

I am researching rain gardens for a new garden design.  The clients live in Richmond, and have a high water table--inches below the surface of their lawn.  They have asked me to design a garden with a rain garden feature, that would tie into a drain.

I have been pondering how to design a rain garden when water frequently sits close to the surface.  If there is no drain, the rain garden will be a pond for most of the winter months.  If there is a drain, where should it be located to be effective?

Rain Garden

Part of my research has been to define the term rain garden.  In fact, a rain garden is a planted garden that holds water for, ideally, no more than 48 hours.  A rain garden may look no different than the rest of the garden, but the soil could be boggy at rainy times of the year.

Dry River Bed

Construction of bioswales on
Blenheim Street, Vancouver

The photographs my clients sent me of their favourite gardens are in fact dry river beds. Dry river beds are not planted, and they may or may not have a lining.  If a dry river bed has a lining, it is designed to move water.  If a dry river bed does not have a lining, it is designed to absorb water, and may have a French drain beneath, which moves water.  A dry river bed should be located at a lower grade than the rest of the garden.






A swale slows the pace of water down a slope. In Vancouver, there are a series of swales on Blenheim street.  Before these were installed, rainfall was channeled down the hill and into drains strategically placed by the road side. Now, the water is channeled into curb breaks, and collects in the swale with much of the water absorbing into the ground.  If too much water is channeled through the curb break at one time, a catch basin at the end of the swale stops the water from flowing over the sidewalk and back onto the street.  The catch basin is higher than the bottom of the swale.  If the catch basin was placed at the bottom of the swale, water would simply collect in that and be swept into the ocean.  The bottom of the swale should be designed with pervious soils to allow water to be absorbed into the ground.

Leaving the leaves in spring

Every autumn, we cover the garden beds with leaves to protect the soil.  Keeping the leaves on site has many advantages.  

1.  Plants take up nutrients, and when the plants die back for the year, if left on site, the nutrients will go back into the soil.

2.  The average rainfall in Vancouver between October 1st and April 30th is 1150 mm or 3.75 feet for the seven months.  The average raindrop hits the ground at 24 kph or 15 mph.  This amount of water hitting the soil creates a tremendous amount of compaction.  An inch of mulch on top of the soil absorbs the impact of this much water on the soil.

3.  If the soil is protected from rain, and does not get compacted, all the useful little critters and microbes stay alive to do their good work for another season.

Often, we are asked when we will be removing the leaves in the spring.  The answer is usually, we won't remove the leaves.  An ecologically designed garden has many tiers of plants covering the soil.  In the spring, as the deciduous plants rise from the soil, they cover the decomposing leaves.  By summer, the leaves have decomposed back into the soil to provide nutrients for the earth again.

The only time we remove leaves is if they are so filled with tannins (i.e. oak, beech), that they will blow all over before they ever decompose.  These leaves go into the compost where their decomposition is accelerated.  These leaves can stay at the back of beds behind or beneath plants, but we do remove them from front entrance or feature beds.

Whenever we can, the autumn leaves get mowed up before being applied to garden beds.  Mowing the leaves speeds up decomposition, and makes the leaves small enough to provide a mulch and allows moisture to penetrate to the soil.

Vancouver rain and soil pH

Vancouver's soil is naturally acidic because of the amount of rain that falls.  

Rain is made of water, which is made of two hydrogen atoms and one oxygen atom (H2O).  When the rain falls to earth, it breaks apart into H+ and HO-.  Now the soil has more free H atoms which makes it more acidic.  

The "H" is pH is for hydrogen.  The "p" has a variety of possible explanations, including power or potential.  

The more free H+ atoms in the soil, the lower the number due to a negative logarithmic equation.  

This part can be confusing, but remember rain = more H+ in soil = high acidity = low pH.

Phosphorous and Hypoxic Zones

This photograph shows the border of a hypoxic zone, or dead zone, in the Gulf of Mexico.  Hypoxic zones are areas of the ocean where all ocean life has been killed off by excess phosphorous and nitrogen.  The excess P and N in the ocean comes from fertilizer run off.

When people use fertilizer that is not absorbed by plants, the excess runs off into our water table and creeks, streams, rivers, etc.  All of these eventually run into our oceans.  If the water running into the oceans has excess nutrients, this creates an algae bloom.  The algae bloom interrupts the normal balance of the ocean by creating an opaque cover over parts of the ocean.

When the algae uses up the nutrients in the water, the algae dies and falls to the ocean floor.  The excess algae decay process uses any oxygen left in that area of the ocean, leaving none for the other life in the ocean.  In turn, this creates a dead portion of the ocean, or a Hypoxic Zone.

Chaefer Beetle = Redesign

Truthfully, we Cultivated Gardeners love the Chaefer Beetle.  We find homeowners are tired of fighting the Chaefer Beetle and call us for help.  We turn the problem into the solution.

What do you do if your lawn is decimated by the effects of Chaefer Beetle larvae?  Here are two options:

1)  If you really need a lawn, then renovate your lawn and learn how to care for the grass so it grows deep roots and is no longer victim to Chaefer Beetle Buffett.

2)  If you don't need a lawn, remove the lawn and plant a beautiful garden.  This is what we like to do.  We have posted some of our garden designs on Houzz.com houzz.com/pro/ecolisa/.   

Many of these designs are a direct result of Chaefer Beetle related damage.  Once their lawn has been decimated, people reassess why they have a lawn, and if a garden would be more suitable.

From the view of maintenance, a properly designed and installed garden is less maintenance than lawn.  If the garden is not properly designed and/or installed, it will be more maintenance than a lawn.

If you are not sure how to design and install successfully, feel free to call us for help.  It is what we do.  www.thecultivatedgardeners.com.

Time to Design

For anyone thinking this is the year to give the garden an overhaul:  now is the time to begin.  

Good garden design begins with a thorough analysis of the garden.  This includes soil analyses, sun/shade audits, privacy/screening issues, wind and microclimate analyses. The designer should also take inventory of the existing garden for healthy plants to retain.

The owner of the garden needs to be collecting ideas for her/his new garden. You can look around your neighbourhood for plants, arbours, fences, and other attractive features that might complement the architecture of your residence.  Alternately, gather some beautiful garden picture books and spend some quiet time reading and dreaming.

Think about how you would like to use your garden:  entertaining, playing, reading, maybe gardening.  How many people will gather in your garden?  How much time do you spend in your garden?  How much time do you want to spend in your garden?

And, of course, the owner of the garden needs to consider a budget for renovations.  A good  designer can create a design to be installed at once, or over a few seasons.  The important part is to have a cohesive design to follow.

Naturally, this is what we do at The Cultivated Gardeners, so feel free to contact us info@thecultivatedgardeners.com.