Materials Needed for Building a Downspout
(Amounts of materials will depend
on downspout planter dimensions.)
- Planter (any sizable container;
for the instructions below, the planter size is 3
x 2 x 2)
- Pond liner (large enough to line
the container with ample slack)
- Soil mix: 60% sand, 10% topsoil,
30% compost (Soil volume = area of container x [height
- Pea gravel: Clean washed gravel
with no fines (Gravel volume = area of container x 4 inches)
- Splash rock / river pebbles (sufficient
to cover an area of 12-18 inches in diameter)
- Bulkhead Assembly DSP3
- Electric drill
- 1 3/8-inch drill bit
- Utility knife
- Channel lock wrenches
- Tape measure
- Survey stakes
Instructions for Building a Downspout Planter:
Step 1. Choosing or Building a Planter:
- A downspout planter can be created out
of any type of sizable container: a wooden box, barrel, plastic
bin, garbage can or watering trough will all suffice.
- The size of the planter can vary depending
on the amount of roof runoff to be collected.
Step 2. Calculate the Size of your Rooftop
that Drains to the Downspout:
- If you do not have blueprints of your
home, you can estimate the area of the rooftop by measuring
the area of the roof (length x width). Do not take the roof
slope into account.
- Calculate the area of rooftop that drains
to the downspout you have chosen. If there is only one downspout,
you can simply utilize the entire roof area.
- If there are gutters with downspouts
on both ends, assume that half of the water goes to each downspout.
Step 3. Determine the Type of Diverter
Technique you Need:
- If the downspout collects water from
an area 100 square feet or less, it is possible for the planter
to handle all of the rooftop runoff. (Option 1, Top Right)
- If the downspout collects water from
an area larger than 100 square feet, it will be necessary to
install an inline downspout diverter (Option 2, Bottom Right/Enlarged
- The diverter will allow you to limit
the flow of roof runoff to the planter.
Step 4. Assemble the Planter Plumbing:
- Install an overflow assembly approximately
2 inches below the top of the planter. It should be located
at the back or side of the planter box. The diameter of the
overflow may range from one inch to 3-4 inches. A smaller overflow
can be used with Option 2. With Option 1, the overflow should
be at least as large in diameter as the downspout itself, in
order to allow ample drainage in storm events.
- Install wide perforated underdrain assembly
approximately 2 inches above the interior bottom of the planter.
The diameter of the underdrain may range from 5/8 to one inch.
Wrap a geofabric sock around the underdrain.
- Both the overflow and underdrain will
reconnect to the downspout stub that remains after
you have cut the downspout (Step 6).
- If preferred, the underdrain can be
connected to an additional pipe or soaker hose that drains to
a pervious portion of the yard, at least 10 feet from building
foundations. This overflow can be used to create a rain garden
Step 5. Assemble the Planter:
- Locate the downspout planter either
immediately below the downspout (for Option 2) or within 4 feet
of the downspout (Option 1).
- Raise the planter high enough off of
the ground by utilizing cinder blocks or other materials so
the underdrain can drain into the riser stub unless youre
draining the underdrain to an additional pipe or soaker hose
that drains to a pervious portion of the yard as mentioned above.
- Install pond liner inside of the planter.
Allow some slack so that soil and gravel do not stretch the
liner as it fills the box.
- Install a 4-inch layer of gravel.
- Install a piece of filter fabric above
the 4-inch layer of gravel.
- Load the soil mix on top of the gravel
and bring the soil surface to approximately 6 inches below the
top of the planter.
Step 6. Disconnect the Downspout and Install
- Option 1: Cut the downspout 2-3 inches
above the planter and install a diverter to allow rainwater
to flow directly into the planter.
- Option 2: Install an inline downspout
diverter that allows partial diversion of roof runoff. This
allows for the diverter to be closed when not in use (during
winter and large storm events).
- Install a 2-3 inch layer of splash rock
(river pebbles) over the soil covering a 12-18 inch area below
Step 7. Planting:
- Select native species that will thrive
in moist conditions.
- Water plants immediately after planting
and continue to water three times per week during the first
two months, and during any period of drought. Wilting plants
indicate a need for extra watering.
Step 8. Maintenance:
- Keep the overflow free and clear of
debris, checking periodically after rainstorms.
- Keep the downspout connection (or diverter)
connected and directed to the planter.
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