In Halifax’s North End, a grassy patch is a rare thing, at
least along the street. And anyone in the area could tell you how much
murky rainwater pools everywhere during a hard rain. A low-impact development
enthusiast might say “Sounds like we need more rain gardens!” But the problem
here is that rain gardens cannot be placed near building foundations because of
the way they pull water down into the ground. This might lead to more basement
flooding. So where, in this dense urban landscape of paved surfaces, can we put
the water?
A typical North End garden and downspout. |
One intriguing option is the stormwater planter box. It’s
essentially a rain barrel filled with gravel, sandy soil and plants, which
collects and holds water, filters it, and then slowly releases it at a
different time than the rest of the rain. Cities all over the world are using
them in dense urban areas as a low-impact development tool. These cities
include: Melbourne,
Australia; Portland,
Oregon; Lancaster,
Pennsylvania; Philadelphia,
Pennsylvania; and Los
Angeles, California. Why not here in Halifax?
One thing you’ll notice is that nearly all the cities
mentioned get minimal snow and ice (with the exception of Pennsylvania). So a
key question for these stormwater planter boxes is how they perform in and recover from the winter. If
they emerge from winter still functioning, then we
have found a valuable answer to this tricky question of where to put rain water
in a dense urban environment.
The Ecology Action Centre Coastal and Water Team has had an opportunity to
build one test stormwater planter box in the Bloomfield area of the North End with
generous funds from our local RBC branch on Almon St. If you want to replicate
the experiment in your own space, here are the steps to take.
Step one: Choose an appropriate location. Select
an area where you can easily disconnect a downspout and re-direct it into the
stormwater planter box. This will look like a relatively flat empty space at
most 2 meters square right next to your house. The two photos above are good
examples of excellent spaces to use.
Step two: Find or build an appropriate container.
You will need a container that can be water-proofed, and can have drainage
holes cut into it, or can be fitted with a drain pipe. Ideal and easiest is an old
water tub like the one below, because it is already assembled and water-proof.
A polyurethane wheelbarrow would also work great, if you don’t mind the
aesthetic of it.
If you like a wooden look, you can try to find one already
assembled, like this one. You will need to water-proof it (read below for your
options on how to do that) and cut a hole for the drain pipe.
If you cannot find an appropriate container, then you can
build your own.
When selecting a container, think about the volume of water
it will receive. You should calculate the drainage area from the part of the
roof that drains into the downspout you will disconnect and send into the
planter box.
This table of sizing guidelines is from Melbourne Water.
Drainage Area m2
|
Planter Box Area m2
|
50
|
1
|
100
|
2
|
150
|
3
|
200
|
4
|
Most North End homes will be in the 50 m2 or less
category, which means that most containers you will find will be an appropriate
size.
We did not find an appropriate box to use, so we built our
own. We chose cedar wood because it is naturally weather resistant. Another
good choice is hemlock. You can use pressure treated wood, as it is much less
expensive but consider that it is toxic. We could only find 2” x 6” lumber,
which in retrospect is a little too sturdy for this purpose, and resulted in a
very heavy box. 1” x 6” lumber would be perfect. You can make your own
construction plans, or use basic carpentry books that feature outdoor/garden
projects to find a plan.
Step three: Obtain
the materials for making the box drain properly. If you’re using a wheel
barrow, all you need is a drill to cut holes at the lowest point in the slope.
Otherwise, you’ll need two drainage pipes: one for the bottom of the box, and
one for overflow. We used a 3” ABS and a 1.5” ABS pipe for the bottom and
overflow respectively. You can find these in the plumbing section of home and construction stores.
To connect them, we used an ABS Tee-Wye like this one. We capped
the end of the 3” pipe inside the box so that it would not clog with gravel and
soil. For the ends that are outside the box (the top of the overflow pipe and
the bottom drain pipe), we used window screen held on with a hose clamp like this one. This ensures
small animals cannot get inside the pipe. For the bottom drain pipe, it is
easiest if you can find one with pre-drilled holes. This is usually made of
PVC. We couldn’t use this because the store didn’t have the other pieces that
would make it all fit together. Because of this, we had to drill our own holes.
If you drill your own holes, make sure they are at least a centimeter in
diameter. We made several rows of holes about 2 cm apart, staggered, on the top
half of the pipe.
Step four: Cut a hole
in the box for the pipe.
Use the end of the pipe to trace the hole. We used a jig saw
to cut out the hole. You can borrow tools like this from the newly opened Halifax Tool Library!
Using a jig saw to cut a hole for the drain pipe. |
Checking that the drain pipe fits through the hole. |
Step five: Cut the
drain pipes to the proper length. The bottom drain pipe should be along the
full length of the bottom, and be able to fit into the Tee-Wye piece, which
will have another short piece (about 7”) of 3” pipe stick out of the hole in
the box. Mark the length, and cut with a small saw like a hack saw, or hand
saw. It’s a good idea to cut into a container so you can easily clean up the
shavings. We just happened to have a kids’ wheelbarrow on hand for this
purpose!
Cutting the drain pipe to the correct length. |
Step six: Waterproof
your box. We were lucky to find a durable plastic liner without any holes
in the hardware store’s waste pile, so we decided to use that. You can also use
sheets of PVC liner taped together, or you can also use a PVC pond liner. We
placed it in the box, and then cut a small X next to the hole for the small
drain pipe. To seal the liner to the drain pipe, we shoved the small piece of
the drain pipe into the Tee Wye connector in a way that put the liner flaps
from the X cut inside the Tee Wye connecter at the edge of the box next to the
hole.
Placing the waterproof liner in the box. |
Step seven: Move the box to
its final location. It should be at least 30 cm away from the house foundation,
and in a location where you can connect a downspout to the box easily.Make sure
it is level and stable. We needed to
do a bit of leveling of the resting area. To do this, we used a shovel, bricks,
and a level to get the box set, and once it was, it would not budge.
Step eight: Prepare for
proper drainage. Without proper drainage, the water will remain in the box and stagnate,
which can kill the roots of the plants. To help angle the drain pipe, we placed
a small brick at the up-slope end to ensure that the pipe was angled down
slightly. To avoid the pipe filling with the gravel which goes at the base of
the box, we stapled the rest of the window screen material around the drain
pipe. Then we filled the first 15 cm of the box with washed gravel in such a
way that supported the slight angle of the drainpipe. We shaped the gravel to
slope down toward the pipe in the middle, and then placed a piece of landscape
fabric over the layer of gravel and pipe. The landscape fabric serves several
functions. It helps keep sand and soil from the top layers from clogging the
gravel and drain pipe, and because it is semi permeable, it helps to direct
water flow into the pipe. We cut small holes in the fabric over the holes in
the drain pipe to help water drain into the pipe. Note that all of these
elements are parts of the experiment. If you decide to take on building a
stormwater planter box of your own, you can decide what elements make sense to
you, observe how they work, and let us know what you find!
Drain pipe ready for draining with brick for the angle, and window screen to keep the gravel out of the drain holes. |
Gravel fill around the drain pipe, and the overflow pipe with its window screen cap. |
Step nine: Fill the box.
Once
the basis for good drainage has been set up, it’s time to continue filling the
box. With the advice of several avid gardeners, we chose to mix a coarse sand
and commerical potting mix together. There was a higher sand ratio at the
bottom of the box and lower at the top where the plants will sit. If you want
to do tests of drainage for different ratios, you can take a couple of unneeded
buckets, cut holes in the bottom, and fill them with different mixes. Then put
an equal amount of water, but enough to saturate them, into each bucket and
observe how quickly they each drain. Soils in a container are too fine and
dense to provide adequate drainage, so potting mix is recommended. To provide
some nutrients and improved absorption, we added a layer of natural bark mulch
on top.
Step ten: Planting!
This
too will be an experiment. We chose to use the very hardy and durable Sedum spectible, which are very popular
around Halifax. We felt this was a good plant to use as a test run to observe
and learn more about the planting conditions in the box through the seasons. If
they perform well, then we will try other plants as well. The plants in the
container need to be cold tolerant to last through the winter in a box that’s
less insulated than the ground, and to tolerate a variable amount of water. You
do not need very many plants to fill a small planter box- maybe 5-6 plants.
Step eleven: Disconnect the downspout and redirect it into the planter box.
You can use a hacksaw to
cut the downspout. To make the downspout reach the box, you can use an
accordion downspout extension tube like this one.
The finished box! |