Garden Detective

How much water does a tomato really need?

Tomato plants need about seven gallons of water per week, spread out over a few deep-watering sessions.
Tomato plants need about seven gallons of water per week, spread out over a few deep-watering sessions. Bigstock

Experts tackle readers’ garden questions.

Q: We recently moved from the Washington, D.C., area to Davis. I have next to no experience gardening, but thought I’d give it a try. About two months ago, I planted three tomato plants. They are growing and look healthy, but so far only one tomato on one plant. I’ve been watering about every other day – just let the hose run gently on each one for about four minutes. But I have no idea if that’s too much, too little, or just right.

Kathy Hoke, Davis

Bee garden writer Debbie Arrington: Don’t worry. Your tomatoes are behaving normally.

When you pick your first ripe tomato depends on several factors including variety and planting date. The earliest varieties ripen in 60 to 65 days. Other varieties, particularly most large heirlooms, need 80 or more days to reach perfection.

Since your vines look healthy and are growing, your plants appear to be off to a good start. Weather may have played a role in their lack of early production. To get fruit, you need blossoms. But intense heat in May and June may have cut down on your tomato vines’ flower power.

According to the University of California’s “Growing Tomatoes in the Home Garden,” tomato plants may drop their blossoms and refuse to set fruit if nights are too cold (below 55 degrees) or days are too hot (more than 90 degrees). Excessive nitrogen fertilizer, lack of sun, or smoggy or smokey air also can cause blossom drop and keep plants from bearing.

Consistent irrigation is key to tomato success. Mature and bearing tomato plants need roughly one gallon per day or seven gallons a week. That water budget is best divided into deep irrigations two or three times a week.

Right now, it sounds like you may be overwatering. Flow rate on hoses vary by length and diameter of hose and water pressure. For example, a 25-foot-long hose with a half-inch diameter and water pressure of 40 pounds per square inch (psi) delivers water at 24 gallons a minute. Even if flowing only gently, that could add up to several gallons in four minutes.

A simple method to check your water flow rate is to get a 5-gallon bucket, a watch and maybe a calculator. Put the hose end in the bottom of the bucket, turn on the faucet to the desired flow and time how long it takes to fill the bucket. If it takes five minutes, the flow rate is 1 gallon per minute. If it takes one minute, the flow rate is five gallons a minute.

Before you water, check the soil for moisture. Use a trowel, long screwdriver or soil probe to see if the soil is hard and dry or moist and pliable. If the soil still looks moist, you can wait a day before irrigating.

Conversely, don’t let tomato plants dry out completely; that leads to blossom-end rot and other issues. Help retain moisture with a 4-inch layer of mulch around each plant.

For more information on growing tomatoes, check out the University of California Publication 8159, “Growing Tomatoes in the Home Garden,” available free online at http://anrcatalog.ucanr.edu/pdf/8159.pdf.

The Bee’s Debbie Arrington, a longtime gardener and consulting rosarian, can be reached at 916-321-1075. Follow her on Twitter @debarrington.

Garden questions?

Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties. Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h&g@sacbee.com. Please put “Garden Detective” in the subject field and include your postal address. To contact UC Extension directly, call:

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