no water? no problem.

Self-watering planters in late-afternoon light || photo by Lauren Mandel

All this talk about high-tech rooftop farming makes my hungry for a good old fashioned DIY project.  Presenting: the self watering planter.

As you may recall from an earlier post, the naked truth,” my Philadelphia row home roof was historically devoid of edibles.  In an effort to remedy this absurdity, my boyfriend and I climbed up to the roof yesterday to get our garden on.  We began by discussing our expectations.  Developing a strategy for infrequent watering was a top priority, as we’ll be away for portions of the summer and don’t want our precious veggies to shrivel in our absence.  With no rooftop spigot, we contemplated capturing condensate from the roof’s AC units to pump through a drip irrigation system.  We also considered bribing friends to hand water while we’re away.  In the interest of cost and self-sufficiency, we ultimately decided that a successful garden would require self-watering planters.     

We next discussed the practicalities of constructing our garden on a roof that we rent, rather than own.  Waterproofing membrane protection was very important, as was avoiding rooftop staining that could result from soil-laden runoff streaming down the roof’s shiny new silver surface.  Weight distribution was another consideration, so we considered the garden’s size and location.  The planters should be wide rather than deep, to minimize weight, and large enough to support multiple crops at once.  We decided to place them along the roof’s south parapet (knee wall at the edge of the roof) to take advantage of a structurally strong part of the roof flanked by a built-in wind break.  

With a rough plan in mind, we headed to a few big box stores to see what creative materials we could find to build our planters, which we hoped would last for years to come.  We searched and searched.  Plastic storage bins at Ikea were likely not food-safe, wood containers at Lowe’s would not have held water, large planters were too heavy and contained drainage holes.

Self-watering planter with internal reservoir || photo by Lauren Mandel

But then, we found it: the Patio Pickers Planter.  This 24″ x 20″ x 10″ plastic bin contains a water reservoir at the base, separated from the planting area by a plastic grate.  Water enters the reservoir through a “fill tube” that extends from the surface of the planter into the reservoir.  Excess water seeps out through overflow holes at the top of the reservoir to prevent the soil and roots from becoming overly saturated.  The planter came with wheels that we chose not to attach; after all, we wouldn’t want our vegetables blowing across the roof!  In its entirety the design is surprisingly similar to that pioneered by EarthBox in 1994.

Step 1 | Buy a self watering planter or acquire a large, food-safe plastic bin and a 2″-4″ thick plastic material to create the reservoir.  An open-cell plant nursery tray or soda bottle tray turned upside-down would provide an inexpensive reservoir.

Cut landscape fabric to size || photo by Lauren Mandel

Step 2 | Cut a piece of landscape fabric at least 6″ larger than the planter’s top in all directions.  For this planter I cut a 36″ x 32″ rectangle.  The fabric itself should be thin and highly porous.  We found an inexpensive fabric at Lowe’s made of recycled plastic bottles.  Creating a fabric “tray” that fits inside the planter requires a series of cuts and folds, and maybe some Duck tape.  First, slit the fabric roughly 6″ from one corner to create a rectangular flap.  Pull the flap until it overlaps completely with the adjacent fabric and creates the first corner.  Hold flap in place with Duct tape or anther tape that grips in water.  Repeat for the remaining corners while pushing the fabric deeply into the corners to prevent air gaps.  Alternate: fold inverted “hospital corners” instead of cutting and taping.

Next, cut a slit through the fabric to accommodate the fill tube.  The design of this planter designates a specific corner, others may not.

 

Place wet soil in corner pockets || photo by Lauren Mandel

Step 3 | Some self-watering planters provide pockets for soil that reach down to the base of the reservoir.  The soil in these locations is intended to wick water up to the surface soil when the reservoir is low.  If your planter contains pockets, line them with landscape fabric if necessary.  Fill the pockets with soil, then wet thoroughly and fit the fabric “tray” back in place.

Fill planter with garden soil || photo by Lauren Mandel

Step 4 | Fill the fabric “tray” with garden soil.  Most off-the-shelf organic vegetable/herb blends are ideal in both composition and capillary potential (ability to wick water).  We used one, 35 liter bag of soil per planter.  Blend compost or other amendments into the soil as you please.

Plant veggie starts or seeds || photo by Lauren Mandel

Step 5 | Plant those veggie starts!  You may alternatively decide to plant seeds, but keep in mind that starting seeds indoors is often more reliable and will allow you to keep more mature, productive crops on the roof.  We planted beets, micro greens, two kale varieties, fennel, basil, chives, and head lettuce.  We’ll plant heirloom tomatoes in an additional container once the starts are ready.

Optional: Before planting secure black plastic over the top of the planter to minimize surface evaporation and weed pressure.  Cut slits in the plastic to accommodate veggie starts, then plant through the slits. 

Fill reservoir with water || photo by Lauren Mandel

Step 6 | Fill reservoir with water using a pitcher, bucket, or hose (if you’re lucky enough to have a rooftop spigot!).  This planter’s reservoir holds 2 gallons of water and will likely need to be filled once per week or twice during heat waves.  We also surface watered to give the plants a boost, and will hand water every morning for the first week until the roots begin to reach the reservoir.  If you installed black plastic over the soil be sure to water each veggie start through the slits in the plastic.

 

Level planters while distributing the load || photo by Lauren Mandel

Step 7 | If your planter has feet, place each pair of feet on a material that will distribute the load, such as a pressure treated pine 2″ x 4″.  Shim the planter as necessary to ensure the reservoir water remains level.

Vuala!  Your DIY self-watering planter is complete!  Now you can put your energy into finding delicious summer recipes for your rooftop produce to share with your friends.

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