For a few weeks now, my favorite meteorologist/horticulturalist Dave Epstein has been tweeting about how dry it’s been. (That rain we had Monday night amounted to barely 1/10 of an inch.) Though the Northeast Regional Climate Center declared the entire northeast drought-free as of May 3, rainfall amounts in Boston have fallen below average for about the past month, which is making me think about (1) how to get our gardens established and healthy now while (2) not wasting any water. (Below, the green line is our cumulative total, up to June 18; the maroon line above it represents “normal.”)
I know I’ve mentioned the advice to water less frequently and more deeply, once your plants are beyond the seedling stage. When the surface of your garden soil is kept continually moist through shallow, frequent watering, your plants’ roots are happy enough hanging out where the water is, leaving them susceptible to drying out if you head to the Cape for a weekend.
But if you like numbers as much as I do, you might still be wondering “how much” and “how often” to water.
One inch per week on average is the number I often see. That’s around .62 gallons per square foot of garden per week.
Here’s the rough math…
- Most of our gardens are 72 square feet, which means we should be giving them around 45 gallons per week. (That sounds like a lot to me, but remember we’re talking about averages here. You may get away with less if your plot is shaded, etc..)
- It took me 40 seconds to fill a 1.5-gallon watering can using my normal hose setting and pressure. (Your time might be different, depending how you use the hoses.)
- 45 gallons/1.5 = around 30 watering can fill-ups. At 40 seconds each, that’s 20 minutes of hose time per week. Again, that’s an average amount.
- You can also try setting tuna cans in multiple locations around your garden and stop watering when they’ve fill to the desired amount.
But there’s more to consider. The soil in New England tends to be sandy and rocky, which means water percolates relatively quickly, beyond our plants’ active root zones, no matter how deep they go. One 20-minute session per week would likely waste a good bit of water and leave your plants dry.
UMass Amherst suggests that watering twice per week should be ample for well-mulched vegetable gardens–for us, about two 10-minute watering sessions–without factoring in rainfall. Or, if you’re using tuna cans, water twice to 1/2-inch.
It takes practice knowing what works well at your particular site/with your particular plants. Every year is different, too. (I’ve been at the same plot for almost ten years, and I’m still figuring it out.) Though morning or evening watering is best, keep an eye on your plants and go ahead and water right away if your soil is dry and your plants are looking droopy on a hot afternoon. Note that squash and cucumbers will wilt under heat stress.
How about rainfall? Here’s our new rain gauge, all nice and level and very empty. For now. When we get rain, we’ll have a better idea of how much water we need to supplement in a given time period.
Old Farmer’s Almanac points out that sometimes the best time to water is right after a rainfall–especially short, light ones–to ensure water penetrates deep.
A few more tips:
- Compost! The organic matter in compost will help retain water.
- Mulch! Use a couple of inches of materials such as straw, shredded bark, chopped-up leaves, seaweed, hulls, newspaper, or compost. Natural materials, in contrast to plastic mulch, for example, add organic matter. (See above.) Keep it away from the base of your plants to discourage rotting.
- I found un-dyed, dark bark mulch from Vermont Mulch Company for $5 a bag at Every Bloomin’ Thing in Scituate. (We used it in our herb garden.) The problem with the dyed stuff is often not the dye itself, but its source, from construction and demolition waste that might contain other nasty chemicals.
- Keep your gardens weeded. Don’t make your plants compete with weeds for nutrients and water.
- Consider intensive planting (reducing the spacing between plants, as appropriate) to create shaded cover over your soil. In some sections of my garden, I don’t have room for mulch because the plants are tightly spaced.
- Old Farmer’s Almanac makes a case for cultivating your soil–roughing it up to help the water soak in. Cultivation may well help in the short term, but in the long term, it may damage your soil structure and lead to more problems with water penetration; also, I’m not sure how well you can cultivate if you’ve applied mulch.
Remember, too, that your plants will need less water as summer moves beyond typical peak water needs in July.
Of course, no matter how carefully you pay attention to amounts and measurements, nothing beats poking a finger down into the soil a couple of inches to see how dry it feels. Is it damp enough to stick together? Try holding off.
Whatever methods work best for you, start planning now. Just in case.
Sources/ More Info…
Food Gardening with Less Water (from the University of California’s UCCE Master Gardener Program, folks with experience dealing with severe water shortages)
A More In-Depth Look at Food Gardening with Less Water (from the same group above)
How Much Water Does My Food Garden Need (again, same group; focuses on the math)
Advice on Efficient Outdoor Watering, from UMass Amherst
Old Farmer’s Almanac tips (includes a chart showing approximate water needs of different types of vegetables)
More tips from Old Farmer’s Almanac
What is evapotranspiration?
Weather data (Northeast Regional Climate Center; I spent way too much time playing with weather charts on this site)
Braintree’s Water Usage Phases