When to Plant Tomatoes in Sunset Zone 18

Temperatures

Growers in Sunset zone 18 experience hot, dry summers with rainy winters. Average winter lows are between 10 and 28 degrees Fahrenheit. The growing season is long, lasting from mid-March through late November. Most plants from the Near East and the Mediterranean do well in this area, as well as hot-weather New World plants such as the tomato. Most of the temperature variations in Sunset zone 18 comes from continental air masses, rather than the ocean.

Sunset Magazine recommends planting tomatoes once the danger of frost has passed and the soil is warm during both day and night. In zone 18, this usually occurs by early April, though it may be possible to set plants out as early as March using hoop tunnels, black plastic mulch or other insulating materials to keep the roots warm at night.

Start tomato plants indoors for faster fruiting and larger, healthier plants. Plant tomatoes from seed beginning 5 to 7 weeks before planting outdoors. Keep seed containers in a sunny window or cold frame, providing temperatures of 65 to 70 degrees Fahrenheit during the day and 50 degrees or warmer at night. Tomato plants do best in full sun. Transplant seedlings to a 3- or 4-inch pot when they are 2 inches high, and keep them in a sunny location until planting time.

Sunset zone 18 has a long growing season that permits two plantings of tomatoes per year. Plant the second set of tomatoes in high summer for harvesting into the fall. Many varieties of tomato plants will bear until the first hard frost kills the main vine. Select more cold-tolerant varieties to extend the harvest later int the season.