Growing tomatoes (Solanum lycopersicum) in Southern California depends on where you live. Due to its geographic diversity, gardening in Southern California spans many climates, from mountains with snowy winters to coastal subtropical areas that are mostly frost-free. The U.S. Department of Agriculture plant hardiness zones go from cold 5a to warm 10b. Rainfall also varies, with average annual rainfall as low as 3 inches in interior deserts to over 30 inches in mountains. Although basic tomato-growing is similar anywhere, you'll need to adjust for your local climate and growing conditions.
Southern California Growing Seasons
Tomatoes are tender perennials grown as annuals, since they're hardy only in U.S. Department of Agriculture plant hardiness zones 10 through 11. For cold winter areas, tomatoes have a short summer growing season, and late-maturing varieties may not have time to ripen, so choose early-maturing varieties. These are also suited for areas with cool summers, or often foggy or cloudy coastal areas. For hot summer interiors, try heat-tolerant varieties. In mild-winter, frost free-areas, you can set out tomato plants in winter months.
Tomato Growth Form
Many short-season tomatoes have determinate growth, which means the plant stops growing after it forms fruit, making a shorter, bushier plant where the tomatoes all ripen at once. Vining, large tomatoes have indeterminate growth, continuing to grow until frost or disease kills them.
For cool, short-season areas, consider determinate "Siberian" tomato, maturing in 60 to 70 days and growing 6 to 8 feet tall. For coastal areas, try determinate "Early Girl," which ripens in 65 days and grows to 18 inches tall. Tomatoes stop setting fruits in hot summer areas when daytime temperatures are over 85 degrees F. Heat-tolerant varieties can help prolong fruit set, with "Solar Fire" producing fruit in 75 days. The determinate tomato forms a bush 4 to 5 feet tall. Heirloom tomatoes with great taste such as indeterminate "Brandywine" do best in areas with longer growing seasons. Reddish-pink 14-ounce tomatoes mature in 85 days.
Start out either by growing tomatoes from seed or by purchasing already started plants. Starting from seed allows a greater choice of varieties than you'd get in seedling tomatoes available in stores. However, if you have limited space for seed raising or limited time, purchasing young plants makes sense.
When to Sow Seeds Indoors
Sow tomato seeds indoors 6 to 8 weeks before the last frost date for your area. This varies widely depending on your hardiness zone. For approximate indoor seed-sowing guidelines, the University of California Extension suggests November to December for desert valleys, mid-January to mid-February for interior valleys, and March to mid-June for coastal areas. In cold locations, times are March through April.
Sow seeds 1/4 inch deep and about 1 inch apart in clean nursery flats with drainage holes. Use a well-draining soilless mix such as half peat and half perlite. Water the container well with a gentle spray and place the flat in a sunny location. Seeds sprout in about seven days if the soil temperature is 75 to 85 degrees F. Sprouting slows at cooler temperatures, taking two weeks at 60 degrees F. Keep the potting mix moist but not soggy.
When seedlings sprout, they have a long, slender pair of seed leaves and then true leaves appear. Carefully transplant the seedlings into pots of their own when they have two sets of true leaves. You can use peat pots or containers such as plastic cups with drainage holes cut in the bottom. Use the same potting mix as for germination. Water the seedlings until water comes out the drainage holes and replace them in a sunny location. Space tomatoes according to their mature size, with bush types at least 2 feet apart and more sprawling varieties 3 to 4 feet apart.
Hardening Off Seedlings
Whether you've raised your own or purchased them, plant seedlings into the garden or into containers when all danger of frost is over. Gradually get seedlings used to garden conditions, called hardening off, by putting the plants where they will grow for a few more hours each day over a period of seven to 14 days. Plants should have about four to six sets of true leaves. Times suggested by the University of California Extension for transplanting are May for cold-winter areas, December through March in desert valleys, March through May in interior valleys, and April through mid-July for the coast.
Provide fertile, well-draining soil rich in organic material. Dig a hole larger than the pot size. Estimate how deep the hole should be by the individual seedling. Bury the stem so only the top three sets of leaves are above ground, removing any leaves that would be buried. The stem forms new roots for stronger growth. Water the plant well, soaking the soil around the roots. If the tomato will need support, put the tomato cage or stake in place.
Light and Watering Conditions
Tomato plants need six to eight hours of sun daily. In areas with cooler summers and short growing seasons, give plants as much sun as possible. In hot summer areas, tomatoes benefit from afternoon shade.
Tomatoes need about 1 inch of water weekly. Keep the soil moist but not soggy. Occasional deep waterings are better than more frequent shallow ones. In arid, hot summer areas, tomatoes may need watering several times a week. Container plants may need daily watering. Mulch tomatoes with 3 to 4 inches of organic material such as grass clippings or straw to conserve moisture.
In colder areas, prepare to protect young plants from possible late freezes. Put containers in a frost-free area or cover garden plants with blankets draped over the tomato cage so they don't touch the foliage. For small plants, use a plastic jug with the bottom cut out.
It's a mistake to fertilize tomatoes early in life with too-rich a nitrogen source, which encourages vegetative growth over fruit formation. When planting tomato seedlings, add 3 tablespoons of an organic fertilizer such as 3-4-6 to the bottom of the planting hole and dig it in. Don't fertilize again until flowers form, and then apply 3 tablespoons of fertilizer per plant twice a month. Scatter the fertilizer around the plants, keeping it away from the stem, mix it into the top layer of soil, and water thoroughly.