Right time to move vegetable plants outdoors

Question

I have started germinating seeds indoors and they are starting to sprout. Once they have their true leaves I am planning to move them to 4" pots and still keep them indoors. I am growing different types of vegetables ranging from kale, lettuce, tomatoes, peppers, cucumber, zucchini, melons, carrots, etc. I live in the San Francisco/Bay area. My question is related to the timing of moving these young plants outdoors into a raised bed. Is there a guide that tells me when it would be safe to move these plants outdoors given the general weather conditions in my area. For example, I have heard that kale, lettuce and root vegetables can be grown in cold weather so those would be safe to move out any time. Others have to wait until the last frost. A definite guide would be helpful to refer to for now and future years.

Answer 1

You can get the average last frost date for your area from various sources, such as this one from UC Ag Extension, or one I cannot seem to find for your area from the National Weather Service.

What that means in any given year is somewhat variable. If you also keep your own records you can in some cases infer patterns from the relationship of the published data to your precise location/microclimate - but to some extent it's always a bit of a dice roll, and having some reserve plants a few weeks behind the earliest ones that you can plant if you need them (due to killing the earliest ones when the weather turns harsh off schedule), or give away if you don't is often a good idea.

Waiting until there's no possibility of frost is also being delayed in roughly half the years when the last frost date is earlier than average. Planting everything on the average last frost date is asking to get whacked in half the years when it's a bit later. The linked page has 10% dates as well, but at least in the colder regions we usually throw a few out there early in case the year is mild, and they'll have a head start, and save a few in case it turns out nasty, with a certain dose of trying to prognosticate the particular year from whatever information we can glean.

You can also do a lot with "floating row cover" or other means (wall-of-water, covering at night with buckets, etc.) of mediating slight dips below frost/freeze temperatures.

Carrots, for instance, transplant poorly (IME) and take cold well, so getting those (or some of those - succession planting works) planted out there sooner rather than later may be beneficial. You may want to direct seed some and compare with your transplants (see if your experience indicates that you'd want to transplant, or not, in future years.)