Maintaining rain gardens--and identifying weeds

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As rain gardens multiply in Madison, their maintenance is a growing problem--no pun intended.

Rain gardens require annual maintenance, to remain attractive and functional.  This means weeding, thinning, and replacement of plants that die.

Rain garden #2 at Thoreau School is growing nicely

The garden is coming along nicely--plants are starting to grow. We survived all the storms !  We've lost only 10-20 plants.

How to build a large rain garden at a school or park

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This is a summary of what we learned during the construction of a large rain garden at Thoreau School.  It was an Eagle Scout project for Jack Nolan, age 14.  It was funded by a $1,500 grant from the Friends of Lake Winga, and supervised by David Thompson.

Attractive plants for shady rain gardens

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If you are building a rain garden in the shade, consider the celandine poppy.

How to build a simple rain garden in one hour !

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You can make a big contribution to safety, lake quality, and neighborhood beauty in only one hour!

Runoff flowing down sidewalk and into the street

Sidewalks are an important link in the health of our lakes. In many places, runoff from storms is channeled down sidewalks, and then into the street. From there, the water washes nutrients and pollution down the stormsewer and into the lakes.

Instead, you can trap the rain and nutrients and use them to grow flowers! By placing a garden next to the sidewalk, you don't have to water your garden.

Gravel gardens that never have to be weeded

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Today I saw my neighbor, John Lewison, at work on his terrace--at 539 S. Owen Drive.  He was halfway through planting a "gravel garden," when he stopped to show me how.

Gravel gardens were developed in Germany, where studies indicate labor savings of 85% over a conventional garden.

Roy's garden

The  concept was presented by Roy Diblik on WPT:  You lay down 5" of gravel over good soil.  Roy used small quartzite chips, because they don't break down.  Other kinds of rock, especially limestone, break down to create soil, which weeds could then invade.  Edging keeps the gravel from mixing with soil or wood chips in the next garden.

Roy planted drought-tolerant plants: Autumn moor grass, Arkansas mint, and prairie dropseed.

The plants are grown in 5" pots, then transplanted into the gravel, by simply pushing the gravel aside for each plant.  They have to be watered every 1-2 days for 8-12 weeks, while getting their roots into the good soil below the gravel.  After that, you never have to water or weed.  Roy says he's  pulled only six weeds in three years from a large gravel garden. 

Although there's no watering or weeding, some maintenance is required.  Fall leaves have to be removed, and the dead crowns of the plants are cut and removed in spring.  This keeps organic matter out of the gravel, where it might create soil.  The garden should last for 30 years.

John's variation

John is modifying the concept to create a rain garden on his terrace.  John hopes to infiltrate a substantial amount of runoff coming from his wide driveway.  During the winter, runoff here makes an icy puddle at a low spot on the sidewalk.

John, a professional landscaper, rototilled the soil, to make it easy to remove.   His plot is about 5' wide by 12' long.  After shoveling out soil to a depth of one foot, he replaced it with 6" of top-quality topsoil. This was necessary because terrace soil below the top few inches usually isn't very good

Then he shoveled in 5" of rounded stream gravel which-- like quartzite--won't break down.

He needed 3/4 of a cubic yard, costing $100. 

Next come the plants.   Stay tuned.

Why rain gardens fail

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Rain gardens are supposed to put runoff back into the ground.

But they don't do their job if the runoff never gets into them, if they overflow before the water sinks in, or if their bottoms are impervious.  I'll address the first two issues here.

Many large rain gardens--for example, those taking runoff from parking areas--aren't graded properly.  The runoff never gets into them.  Obviously, no one is checking to see if they really work.  I'll give three examples from parking lots.

Metcalfe's Sentry

In this large lot, there are 3-4 long islands between rows of parking, which are supposed to receive runoff from the gutters through gaps in the curb. 

These gardens fail because the basins aren't much lower than the gutter.  No water flows in.

And, there is nothing to deflect the swift flow in the gutter towards the garden.

Madison Gas & Electric visitor's parking

At this lot, we have--at the center of the lot--a filtration chamber.  It was designed to filter the toxic stuff dripping from vehicles, before the runoff gets to nearby Lake Monona.  The filtration was a cooperative project by MG&E, DNR, and other agencies to see how efficient filtration could be.

The filters reside in an underground concrete bunker--the setup cost $50,000. It basically does the job a larger rain garden could do.

 

While this wasn't a rain garden, they did measure how effective the parking area was at gathering water and feeding it to the filters.  Since the parking area wasn't graded to be an effective catchment basin, it sent 30% of the water to surrounding streets.  Only 70% of the water falling on the pavement actually went to the filters.

The area within the red line drained to the filters. The area between the red and yellow lines drained to the street--wasted.

So a rain garden (or filtration system) is no more effective than the grading and inlets to the garden.  If the grading isn't carefully done, you've wasted a lot of money.

Terrace rain gardens on Eaton Ridge

These were among the first rain gardens on terraces, built by the City.

Rain garden inlets on Eaton Ridge were too small, and quickly became clogged.

 

Terrace gardens built by the City on Adams St had better entrances.

Sequoya Commons

This is a beautiful rain garden, with a large capacity.  For the most part, it is well-graded.  Nevertheless, a small portion of the north end of the parking area drains to the street, via the entrance to the lot.

 

My real purpose for mentioning Sequoya is that you can see this garden does reject some water.  I saw if overflow once in a heavy storm.

On another occasion, when the garden was full of water, a steady stream of clear water seeped from the garden into the storm sewer.  While this escaping water didn't get into the ground, at least it was clean and free from sediment.



The bottom line

Before you build a garden, always watch where the rain goes during a storm. 

Test the grade by pouring water on the pavement.

Don't pay the contractor till you see if the garden actually works.

If necessary, build a berm of earth or asphalt to correct the flow.