When Do I Plant My Tomatoes?
The age old question: When do I plant my tomatoes? Heck, I don't know. Every year is different. Tomatoes do not like cold weather. If they are chilled for a prolonged period of time, they may not die, but they may become stunted, or their growth may be slowed so that later plantings will overtake your earlier plantings. You want to plant when your soil temperatures are at least 50, & preferably 55. Raised planters generally warm up faster than the flat ground, especially if they have an unimpeded south or west facing exposure. The University of California's Master Gardeners program recommends May1. Check this link for vegetable planting guidelines for Contra Costa County Sunset zones 14, 15 & 16. Most of Orinda, Moraga and Lafayette are zone 14 with some 15. https://ucanr.edu/sites/ccmg/files/131284.pdf
Can you plant earlier? Of course you can. If you have a favorable microclimate, you can plant sometimes much earlier. South & west exposures are warmer than east or north exposures. If you are elevated above the valley floor, you will be warmer than the valleys & hollows. You can prewarm the soil by turning it over and covering it with clear or red plastic. You can plant in a tomato cage & wrap it in clear plastic, or you can use wall o waters. You are almost always safe on May 1; you are probably safe on April 15; you are sometimes safe on April 1; you are rarely safe on Mar 15. My advice is, if you don't want to do anything special, wait until April 15 & look at the long range forecast. If its going to be cool, wait. If its going to be warm, plant.