Marin Master Gardeners
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Marin Master Gardeners

Marin IJ Articles

April's the month to plant for a summer full of tasty tomatoes

April 09, 2011
Anne-Marie Walker

IN THE GARDEN on a summer's day, the buzz of the bumblebees is a welcome sound for tomato lovers. Tomatoes are among the 8 percent of flowering plants fertilized not by honeybees but instead by bumblebees.

Often referred to as "buzz pollination," the process works by sonication; sound waves that shake pollen free from the anthers to the pistil and stigma. The vibration is not caused by the bumblebee's wings, but rather by its breathing achieved through four holes, called spiracles, in its abdomen. If you don't see bumblebees in your garden, encourage them by planting an herb border of borage, rosemary and chives whose blue flowers attract the bumblebee. If fruit is still not setting, you can accomplish pollination with a gentle tap of your hand or wait for a bit of wind.

The tomato, indigenous to the Andes, was domesticated in Mexico and brought to Europe by the Spanish. The name tomato derives from the Nahuatl language spoken by the Aztec. The first written description of the tomato was in 1544 by Pietro Andrea Matthiola, a Tuscan physician and botanist. He described it as the "mala aurea" or golden apple.

Cultivation of the tomato spread throughout the Mediterranean, where the climate was supportive to growth. The oldest known European recipe for tomatoes (recorded in Italy where the fruit was eaten universally) was called salsa di pommodoro alla Spagnola, literally meaning Spanish tomato sauce.

Technically, tomatoes in the wild are tender perennials with tiny leaves and sweet tiny fruit that grow in clusters much like grapes. Their growth pattern is indeterminate and the plants have a low, spreading habit making them perfect candidates for hanging baskets.

We choose to grow tomatoes as warm weather annuals. Varieties of tomatoes are numerous and are categorized by vine habit of 'Indeterminate,' 'Large Determinate' and 'Determinate.' 'Indeterminate'
vines grow and set fruit throughout the season and need good trellis support. 'Large Determinate' vines grow to a good size but not that much after that. 'Determinate' vines remain small to medium in size, and compact or dwarf vines are even smaller. Leaf size and canopy also vary by variety as do resistance or tolerance of diseases.

So, a little homework before selecting your tomato variety can truly pay off.

There is a reason that the homegrown tomato is one of the most popular garden vegetables (although technically a fruit as it is a ripened ovary) and that is flavor. Home gardeners select for taste whereas commercial growers select primarily for tough skins that hold up in shipping and secondly for bright color to attract the eye of the customer. Besides selecting for flavor, select for resistance by looking for the identification codes on the label following the cultivar's name.

There is no cure for the following conditions other than resistant varieties and good garden hygiene. Disease-resistant codes include:

• A: Alternaria stem canker — dark brown/black cankers on stems and leaves

• F: Fusaruim wilt — soil-borne fungi that yellow, weaken, stunt or kill tomato plants (FF or FFF are also Fusarium)

• N: Nematodes — tiny wormlike root parasites make leaves turn brown from bottom up

• T: Tobacco mosaic virus (TMV) — causes irregular light and dark green pattern on leaves

• St: Stemphylium — gray leaf spot

• V: Verticillium wilt — soil-borne fungi makes older leaves turn yellow

As Master Gardeners, we know the mantra, "right plant, right place." If you want a bountiful tomato harvest, there is no greater truism. Plant your tomato seedlings when the danger of frost has passed. In Marin, late April or early May is a good time. Fruit set occurs in tomatoes when nighttime temperatures are above 55 degrees and daytime temperatures do not exceed 90 degrees.

Planting in the late afternoon minimizes water loss. Select a spot that gets about six hours of full sun, dig a hole about 24 inches deep and fertilize the soil with calcium and fish emulsion — a fish head and ground up egg shells work well.

Tomatoes grow best in nearly neutral soil with pH of 6.5 to 7.0. Pinch off the lower leaves, handling the plant only by its leaves or root ball and set the plant in the hole with just two sets of leaves showing above ground. Back fill carefully as roots will form on the buried portions of stems.

Finally, keep the soil around your tomatoes moist the first three to four weeks. Water-established plants deeply when the soil dries to about 2 inches, usually twice a week to once every 10 days.

After the first fruit sets, sidedress the plants with nitrogen fertilizer once every four weeks. You'll enjoy your sweet-tasting bounty in about 70 to 90 days. During a cool spring or fall, watch for catfacing; when temperatures rise, watch for failure to set, catfacing and sun-scald discoloration the skin. You can best control these problems by maintaining plant vigor, even soil moisture and providing partial shade.

During a dry spell, control blossom-end rot, the result of lack of calcium in the fruit because of plant stress, by maintaining an even soil moisture and a balanced fertilizer; 5-10-5 is adequate.

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