Soil temperatures control when different seeds will germinate. Cool-season vegetables, such as peas, carrots, lettuce, spinach, and mustard will germinate when soil temperatures are cool, from about 45 - 60 degrees Fahrenheit. Warm-season vegetables such as tomatoes, peppers, squash, amaranth, and cucumbers like to germinate when soil temperatures are above about 65 degrees Fahrenheit. Some farmers get a jump-start by starting their Summer vegetables in a warm greenhouse, in a sunny indoor window, or by using a heat mat. Our farm, however, gardens naturally outdoors by the seasons and we grow our seedlings in composty soil in flats on the ground.
This year is presenting a bit of a challenge getting our Summer cops planted as soil temperatures are several degrees below average as we enter Spring. Things could change quickly and soils will get warm enough to germinate our warm-season crops if the rains abate and we get some more sunshine. This year's Old Farmers Almanac still predicts that we will have a hotter than average Summer. https://www.almanac.com/weather/longrange/zipcode/94803
Weather is a variable that we have little to no control over, yet it influences our growing season dramatically.
Seed suppliers will often provide instructions with their seeds that include the optimal seed germination temperatures. Here is an example from Johnny's Seeds for the optimal soil temperatures needed for germinating Preludio fennel, which is one of the vegetables we grow at our farm.
A grower can use an instant-read meat thermometer and insert the thermometer probe about 1/2 inch into the soil to get the actual soil temperature.
We refer to our seed starting calendar for our micro-climate's average growing conditions, however we also consider the soil temperature and current weather conditions for adjusting when we plant seeds of different vegetables, flowers, and herbs.
You may purchase our seed starting calendar at this link: https://www.cloverfieldfarm.us/product-page/cloverfield-organic-farm-seed-planting-calendar
Please come visit the farm and we will show you how we do our seed starting and planting. We have a nice variety of certified organic edible plants available for purchase in pots. We are located at 501 La Paloma Rd., in El Sobrante. We are open (during Pacific Daylight Savings Time) on Fridays, Saturdays, and Sundays, from noon to five pm. Alternate times to come visit can be reserved on our website. https://www.cloverfieldfarm.us/book-online
Hope to see you soon!