How often do I water my tomato plants? That's probably the most often asked question I get. The answer is: it depends. It depends on several things: the age of your plant, the weather, your climate, your soil type, and container growing. I know people would love me to tell them: "Water it three times a week," or some other schedule that suits them. But that would be a disservice to you and your garden. We don't have our garden on a schedule. We make an assessment, bed to bed, and day to day. If we find we need watering, then we water.
1. Age of plant: newly-planted tomatoes need more frequent watering than older, more established ones do. It's not only because the root ball hasn't had a chance to explore the great outdoors yet, but it's also because root balls closer to the surface obviously dry out faster than those further down.
2. The weather: How can you put your garden on a timer, when you can't predict the weather? If the days are cooler, then less watering is required. If you've got a foggy environment, then less water is required. If it's been blazing hot, then yes, of course, the garden needs more water. Ag statistics show that 75% of plant deaths are a result of improper watering.
3. Your micro-climate: Not only do coastal areas need less water, but if your garden is shadier than your neighbor's, it'll need less water as well. There are 6 or 7 micro-climates in Santa Cruz County, and each requires a bit of skewing of water needs. Then individual gardens vary, too. Some of our garden beds that get afternoon shade need less water than the ones that get all day sun.
4. Your soil type: If you've got a clay pan below your top soil, then you may be watering too much. I planted tomatoes in a clay-type field one year and found I only had to water them once a month. In my sandy-loam soil in Ben Lomond, we had to water more often. Added organic matter and humic acid to both clay and sandy soils help water retention and drainage. We always add lots of compost to our beds before planting.
5. Container growing: Plants in containers are completely dependent upon you for their moisture and fertility. Don't drop the ball and stress the plant by allowing it to dry out too much between waterings. Water stressed plants will have reduced vigor and reduced fruit yields, even if you only blow it a couple of times.
My best advice on watering is to check the soil. The very first time we transplant a plant, we ensure that we have wetted the soil at root ball level thoroughly. That may mean standing there with the hose for half an hour. It may mean wetting the planting hole before watering too. You may need to water for five minutes, walk away for a few minutes, and then come back and repeat. Different soil types accept water at different rates. This scholarly article discusses actual retention rates and is a fine primer for people interested in watering properly.
After your initial day's watering, your plant may not need watering for a while. If the soil surface is dry, dig down a little and check. I don't water my young tomatoes until the subsoil is dry to a depth of about an inch. With older, more established tomatoes, I will check and if it is dry several inches below, then I water.
When you do decide to water, try to do it in the morning, as plants that are watered just before dark are more susceptible to fungal diseases. We also don't get the foliage wet, as that increases disease as well. Lightly spraying the soil isn't desirable at all, as you're only wetting the top few centimeters, not deep watering, which is recommended.
So my best tips: back off the watering, don't use timers, check check and double check! Then water deeply. If you're interested in installing a simple, yet effective, drip irrigation system for your vegetable garden, consider coming to our Drip Irrigation Workshop.
Cynthia - Do you use a moisture meter to stick in the soil to measure the moisture? I'm wondering what the best method is to determine how much to water. I think this is where I go wrong every year.
Thanks.
Posted by: Arlyne Semiloff | May 22, 2011 at 09:00 AM