By T. Eric Nightingale, UC Master Gardener of Napa County

Spring is finally here and that means that tomato season is around the corner. Don't get too excited, though. Even though seedlings will be showing up in nurseries, it's best to wait to plant them.

Tomatoes need warm air and soil, as well as a lot of sunlight, to grow strong and healthy. Planting too early can leave them spindly and weak.

Should you want to be sure the time is right, test the soil temperature with a soil thermometer. It should be 60°F or more at a depth of two to three inches. Usually this occurs in early May.

Choosing a proper location for your tomato garden is important. The spot should get several hours of sunlight each day. You may have a prime spot but don't overuse it. Like other members of the nightshade family, tomatoes nurture the soil fungi Fusarium and Verticillium. The soil can become infected if tomatoes are planted in the same location too many years in a row. Rotating your tomato planting locations, or changing out the soil in a raised bed, will prevent the fungus from affecting your vegetables.

Plant tomatoes deeply. First, remove any leaves below the top eight inches. Place the seedling at a slight angle in the hole so that only the top eight inches sit about the hole. The plant's buried stem will push fresh roots, giving the young plant increased access to water and nutrients. Tomatoes also need a good deal of room to grow, so plant them at least two feet apart.

After your seedlings are all snug in their beds, they need some nurturing. If you are concerned about hungry animals or other threats, cover the tomatoes with the top half of a large soda bottle. Not only can this keep them from becoming someone's midnight snack, but it provides them with a personal greenhouse to keep them warm.

Tomatoes thrive with water, especially in the early days. Make sure to give them enough that the water soaks deep into the soil. This will ensure the plants get enough water immediately but will also encourage their roots to follow the water deep into the soil, helping the plants stay hydrated later.

As your plants grow, they will likely require support. Some tomatoes are “determinant” and grow into a shrub only a few feet tall. Many others are “indeterminate,” however, and will continue to grow like a vine until cold weather arrives.

For these motivated climbers you will need a tomato cage or other device. I have used a few stakes placed in a circle around the plant, with loose string or plant tape strung between them. This structure provides enough support while also allowing me to easily harvest the fruits of my labor.

Tomatoes can self-pollinate, so it's possible to get fruit while growing only one plant. The pollen still needs to move from one flower to the next, though. To be sure this happens, give your plants a light shake every morning. This jostling will knock some pollen airborne and help the process along.

One common disorder often seen on Roma or elongated tomatoes is blossom-end rot. You'll recognize the symptoms when you see fruit with an ugly brown sunken circle on one end. This condition can be caused by heavy applications of nitrogen fertilizer and extreme fluctuations in water supply. To avoid this problem always use a fertilizer with balanced amount of nitrogen and phosphorus and provide regular deep watering. Use a mulch around the base of the plants to reduce the loss of moisture from the soil.

Healthy transplants should not need much fertilizing until flowering and fruit set begins, too much nitrogen will give vigorous leaf growth delay flowering. Use a balanced fertilizer to grow healthy tomatoes, Nitrogen, is the nutrient responsible for leaf and stem growth and phosphorus for bud development.  Fertilize every 4-6 weeks following the instructions on the label. Avoid applying more than is need so extra fertilizer doesn't leach beyond the root zone and
into the ground water. 

Experiment and find what practices work best in your garden. With hard work and a little luck, you will be on the path to a bountiful harvest.

Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County (http:/napamg.ucanr.edu) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.