I volunteer for a large system of community gardens in Chicago– 664 plots at four sites. I see a lot of poor cultural practices when it comes to watering, so here’s some tips for proper watering, especially if you have raised beds:
How to tell when the plot needs water
The surface soil is not an indication—unless you have mulched (which is a good idea, more below), the top inch or two will always dry out in the absence of rain. Dig down about two knuckles deep. If the soil there is dark and even slightly damp, give it another 12 hours and check again. Soil should not stay muddy, wet, or so damp that it’s hard to dig through with your hand—this is too much water. If the soil is dry a full finger’s length down, it needs water.
How much water should I give it?
Rule of thumb is 1” per week (NOT 1” per day as a gardener suggested to me a few days ago). Based on a very unscientific watering test in my backyard, this seems to be about 8 to 12 gallons (4 to 6 watering cans full) for your 4x8ft bed. I would err on the side of too much water if you know there is no rain in the forecast. Rain counts—if you get an inch of rain, you don’t need to water. If you get a half inch, you don’t need to water as much. Watch the weather report.
Where should I water?
Water the base of the plant. But this does not mean “only the base of the plant.” It means “don’t water the leaves.” Water ALL of the soil, not just the area immediately around the plant. Remember that the roots are spread out throughout the soil. Watering in just one spot will encourage the roots to stay there, where the water is. Make the plant work a little to get a drink.
Why not water the leaves?
Especially on hot days, if there is water on the leaves it can actually burn your plant. Further, leaves get their water from the soil, relying only secondarily on the humidity in the air. Don’t be alarmed if your plants are droopy in the midday heat—they are conserving water where it counts—in their roots—and letting the extremities suffer a little. If you come back in the evening, they’ll be all perky again.
Seeds and seedlings
Seeds need to be moist, but not soaking. The problem is they are in that surface area that dries out. Once you water seeds, you have to keep that top couple of inches damp until they sprout. If you water them too much, however, they’ll just rot. If they germinate and then dry out, they’ll die. Be aware of how long it takes seeds to sprout—it’s different in different plants, so you can be aware of how to water. Water your seeds shallowly and your seedlings deeply.
If you’re getting puddles when you water, either you’re watering too fast, or you’re watering too much. Watering cans deliver a lot of water in a short amount of time, not giving the soil time to absorb it, so it just pools on the surface. Water very slowly, and wait a few minutes between cans of water to allow it to seep into the soil. Use the spout cover; don’t remove it so that you can water faster. Especially on hot days, water sitting on the surface of your plot is just going to evaporate.
Should I water after a rain?
If it rains a full inch, you’re good for a week. Do the finger test a day or two after the rain, and keep in mind the weather. If it’s especially hot or windy, the soil will dry out faster.
I confess. I water using sprinklers when it’s really dry like this. But I have a large garden (23×70 feet) and crazy curvy beds making a drip irrigation system nearly impossible. If you water with a sprinkler, do it in the early morning. When we’re getting adequate rain, I barely water my very mature garden at all because the plants themselves hold the moisture in the earth just fine. When I do water, I use cached rainwater, and yes, I carry the watering can back and forth. It’s good exercise.
Yes. Nice mulches are: mushroom compost, cocoa shells (remember not to use cocoa shells where dogs, ducks or other precious critters might ingest it. I’m not so concerned about the squirrels and wild rabbits), leaf mold, “black forest mulch” (shredded leaves and wood). Do not use peat moss (water will run right off of peat moss, defeating the entire purpose, plus it’s not a renewable material), pebbles, bark, or wood chips. Once your plants are large, their own foliage becomes the mulch and helps to hold the moisture in the soil.
Best time to water
Water in the early morning or early evening (but not too late. You don’t want the sun to go down on wet foliage). If you water at the height of the midday heat, a lot of the moisture will simply evaporate and your plants won’t get the full benefit of what you’ve given them.
What are your best watering tips?