Happy summer to you! My vegetable garden is in, I’m eating radishes and lettuce every day, new perennials are planted, the final large section of grass I had in my yard is sheet mulched, and we finally got some much-needed rain this week. Garden season 2021 is well underway!
I helped teach a vegetable gardening basics class online earlier this spring for Hennepin County Master Gardeners. It was really challenging adapting our curriculum and teaching style to the online format, and it gave me a whole new appreciation for what school teachers have been through during the past 12+ months.
In creating our section on watering, we looked at current U of MN recommendations, and discovered that the U does not recommend using rain barrel water on your vegetable gardens.
The U has good reasons for this—one is that birds and squirrels regularly defecate on your roof, and rain washes all those feces into your rain barrel, where the bacteria has a nice warm and wet environment in which to thrive.
Additionally, depending on the material and age of your shingles, various chemicals can also wash down those downspouts and into your barrels. A study in Seattle found that runoff from asphalt shingles was cleaner than the researchers had anticipated, while runoff from wood shakes was basically unusable because of high arsenic levels.
All of this makes sense to me. Yet, I’ve been watering my vegetables, fruits, perennials, and pretty much everything else in my yard with rain barrel water for 10+ years. Have I been unwittingly putting myself and my family in danger?
On the other hand, as I thought about it, I realized that I do employ some strategies with my rain barrel water that help mitigate those risks.
The most obvious one is: don’t ever rinse off produce with rain barrel water and then immediately eat it. Just like you wouldn’t drink water from a garden hose or rain barrel.
The next biggest one is this: avoid using rain barrel water on anything I’m going to eat in the next 5-7 days. I see little to no risk in using rain barrel water on, for example, the tiny leeks in my garden right now that I won’t be harvesting until September. I’ll probably use rain barrel on them until at least August. Allowing some time between watering with the barrel and harvesting allows for bacteria to be killed by our favorite bacteria-killing friend: the sun. Additionally I always, always wash produce inside the house with tap water before eating.
I have lots of fruit-bearing trees and shrubs and I can testify how much happier they are with rain water. Even the U of MN says it’s fine to use rain barrel water for fruit trees and shrubs, as long as you water in a way that doesn’t splash up onto the fruit. My favorite way to water trees and shrubs from the barrel is to hook up a hose to it and let the barrel water run out onto the ground.
As a master gardener, when advising the public, I have to stick to research-based University of Minnesota recommendations. And research shows that rain barrel water *does* have bacteria in it. But the research is also not completely conclusive on this—Rutgers University did some research and concluded that in most circumstances, it’s perfectly safe (they recommended strategies similar to the ones I recommended).
Unofficially, if you are a person who can handle nuance, and employ some risk mitigation strategy, I am prepared to say that, in my personal anecdotal experience and on some actual research that does exist, rain barrel water is OK to use on fruits and (to a lesser extent) vegetables. It’s not a must though—if you’re uncomfortable with it, then by all means just use your rain barrel water on your trees, shrubs, perennials, and houseplants. They’ll thrive on it.
Clear as mud, right? I’m very curious how many other people use rain barrel water on their vegetables and other edible landscaping, so please comment if you do. I would love to see more research done about it.
Coming soon: I’ll start working on my annual Memorial Day garden photo shoot tonight, so watch for that post early next week.