What is it called when a Container Garden and a Rain Barrel have a baby? ….
A Downspout Planter!
Materials Needed for Building a Downspout Planter
(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 – 10 inches])
- 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
- 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 Here).
- 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 (pages 24-27).
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 you’re 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 Downspout Diverter:
- 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 the downspout.
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.