vegetable planting in swale

Asked July 26, 2020, 4:51 PM EDT

Hello. I have a home built in 2016 that included a roughly 10 x 10 ft "planter" for run off water control from the roof, which is finished with a low profile composite material. The planter came with (and still has) a watering system (was in ground sprinklers which I converted to drip system) to assure the grasses that were planted in the planter at house purchase would grow nicely when there was not likely going to be much run off (such as now). It seems to me at least some of the planter could be used to plant edible vegetables. Is that legal, not advisable, and/ or reasonable with certain precautions or caveat, or ??? Thankk you in advance for your knowledgeable response. Lawrence

Multnomah County Oregon

3 Responses

Hi Lawrence,
It is not recommended that people grow vegetables in stormwater planters or rain gardens. They are designed to treat the runoff by using plants and soils to absorb nutrients and other compounds from the water passing through the systems. Even though the water is diluted and the amount of particles is low compared to runoff from industrial areas, it is not recommended the water or area be used for any type of consumption (e.g., vegetables, storing water for human/animal consumption).

You could enhance the planter by establishing a wider variety of plants for color and to attract pollinators. Cities usually design these areas with limited types of plants to make them easier to maintain. Landowners can enhance them as long as they are not filled in with more material (i.e. soil, rock). Site the plants based on the amount of water and light they will receive. The outside edges are good places for drought tolerant plants, while the lowest elevation areas are good for plants that can withstand periodic inundation.

I commend you for actively maintaining the area. They are often ignored by new owners that do not understand them or maintain them.

Good luck on your project.

I appreciate your help.
Would it be a problem at all if I put a wood deck ( with space between each board) over parttpart or all of the planter to make it an outdoor lounging space ?

Hi Lawrence,
The two issues to consider are space and sunlight.

The planters are designed to hold and treat runoff from about 85-90% of the storms in the area (small to medium sized storms). If someone fills them in, then the capacity will not be as much. I see this happen quite often. Your deck sounds like it will be above the planter, so that is not a big deal.

The plants were chosen based on the typical amount of light the planter receives when initially built. If your deck decreases the amount of light, then the plants that are shade intolerant will not do well. They may die or be taken over by weeds. I am not familiar with the restrictions on how to manage the specific planters in your area. It makes sense to me that you could establish more shade tolerant plants to replace the ones that are affected. The planter would continue to provide treatment but with different plants. The City of Portland should have a guide for what types of plants should be used in planters and rain gardens.

Feel free to email me directly - rather than go through this Ask an Expert system. My cell phone is 503-510-7582.