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Marin's weather often to blame for paltry tomato crop

  • Nanette Londeree
  • Those plump, juicy, crimson orbs of summer - there's nothing quite as good as biting into a warm, sweet, perfectly ripe tomato. John Denver's refrain in his song "Homegrown Tomatoes" says it just right:

    "Home grown tomatoes, home grown tomatoes

    What would life be like without homegrown tomatoes?

    There's only two things that money can't buy

    That's true love and home grown tomatoes."

    I don't even bother with grocery store tomatoes any more. Those rock hard, mealy fruits that decorate the supermarket counters winter through spring are poor imitations of the real thing. Growing your own is easy to do - find the right spot, get a seedling of your favorite variety, plant it, water it, support it and indulge in summer's taste treat.

    One of America's favorite vegetables (though botanically a fruit) is part of the daily diet for many of us - whether eaten fresh off the vine, sun-dried or added to a plethora of cooked dishes, it's a delicious and easy way to get a regular dose of vitamin C.

    So here it is mid-August, you planted your seedlings, diligently tended them for the past couple of months, and yet, no tomatoes! Or, if you've got some, they're sitting on the vine like little green marbles.  Maybe they're finally turning color but have cracks or black splotches. What's up with that?

    If your tomato plants are not generating your highly anticipated bounty and your frustration level is increasing, you're in good company. Lots of people have been calling the Master Gardener Help Desk describing their sulking plants and wondering what's going on.

    The good news is it's not a result of some pest or disease. Instead, it's likely a result of our weather. These South American natives grow best with at least four to six hours of full sun and relatively consistent warm, not hot, temperatures. They are particularly sensitive to low night temperatures, one reason not to plant them too early in the season. This summer has been on the markedly cool side

    spiked with a few sizzling days. These roller coaster-like temperature swings can play havoc with your summer crop.

    Here are some of the more common, environmentally-induced maladies of tomatoes.

    No fruit

    Temperatures below 55 degrees or above 90 degrees can cause tomato flowers to fall off or fail to set fruit; too much shade can also result in no fruit.

    Poor color development

    The best red color develops when ripening occurs between 65 and 70 degrees.  Summer temperatures that are too high will speed up ripening and produce fruits that are more orange than red. Prolonged cool temperatures slow down ripening so fruit stays green. Green "shoulders" with the rest of the fruit red can follow hot days or very high light intensity. White, yellow or leathery brown patches on the side of the fruit are symptoms of sunscald, the sudden exposure to direct sunlight in hot, dry weather.

    Misshapen or malformed fruit

    Circular, concentric or radial cracks from the stem end of the fruit appear when there are significant differences between day and night temperatures, periods of rapid growth during high temperatures or wide fluctuations in soil moisture. Catfacing (misshapen or malformed fruit at the blossom end) causes the fruit to pucker and have deep crevices, and can show up after abnormally cool or hot conditions. Those same conditions during pollination can result in puffy fruit that look more like bell peppers. A small water-soaked spot near the blossom end of the fruit (blossom end rot), may be apparent when calcium is not readily available to developing fruit due to fluctuations in soil moisture.

    So what's a gardener to do?

    First, know your varieties. Some types have unusual coloring or physical shapes that are characteristic of the variety, especially the heirloom types. The days from planting to ripened fruit also vary with types. Brandywine tomatoes, for example, begin to ripen nearly three months after seedlings are set out.

    Next, be patient. If you've got fruit on the vine, time should yield ripened fruit. Picking tomatoes before they have a full, deep red color can reduce the likelihood of cracking.  If you've got some less than perfect-looking fruit, most of the apparent damage is cosmetic - it shouldn't diminish the taste of the fruit. Just cut out any portion that is undesirable. And remember, since tomatoes don't like cool temperatures, keep those fresh ones out of the refrigerator. Below 50 degrees, flavor can be greatly diminished.

    While there's not much you can do about the weather, you can continue to provide your plants with plenty of sun and adequate, consistent water. Protect precious fruit on particularly hot days with shade cloth or screening material and avoid over-pruning the plants, allowing leaf cover to shield fruit.


    If you like sleuthing, trying to figure out what's wrong with your tomatoes and vegetables, other food crops, lawn, trees or other garden plants and sharing what you learn with others, you might be interested in becoming a Marin Master Gardener. Applications are now being accepted for the 2010 class. You can learn more about the program by attending one of the upcoming informational programs; the first is at 2 p.m. Aug. 20 at the University of California Cooperative Extension Office, 1682 Novato Blvd., Suite 150 in Novato. The second is at 6 p.m. Sept. 3 in the Livermore Room, Marin Art and Garden Center, 30 Sir Francis Drake Blvd. in Ross. For full program and registration information visit the Marin Master Gardener Web site at www.marinmg.org.