You might Google your city/county for “average last frost date,” or contact your nearest agricultural extension office. Here we have quite a few Master Gardner volunteers who can offer good advice.
San Antonio has an average last frost date of 15 March. But Googling before posting this reply I noticed a few sites list our average last frost date as falling on 23 or 24 March. We had a few late freezes last year, so averages being averages, they can change.
Some good advice I’ve never strictly followed is to wait two weeks after the average last frost date before transplanting. Usually by the time I transplant everything I’ve hit that two week waiting period. And, I compulsively seed far more plants than I possibly could ever fit into my little backyard garden. Can’t seem to help myself. If I get surprised by a cold snap, I’ve got plenty of reserves to take their place.
Good advice.
And I suppose if you plant late, even four weeks after the actual last-frost date, you’ll still get a crop, right? It just may not reach the fullest potential because it will be growing later into the season (that is, when the cold weather returns)? Would this be correct, or do crops have a peak and if you plant too late, you simply miss it and will not have a crop?