I will admit I'm not really organized, and would probably benefit from being so.
I have general rules of thumb on when plants can be planted, and work backwards from the information provided on the seed package as well as experience.
In my area, I can plant salad crops out in late April. Since I have DIY low tunnels, I can get away with late March or early April for planting, and then back up 6 weeks or so for seed starting.
Tomatoes can go out end of May, so they are typically started mid to late March., Peppers take foreve to get to a reasonable size, so should be started earlier than the tomatoes, but since I'm lazy, they tend to get planted the same time and then I curse myself for not starting them earlier. Peppers really can't go out around here until the beginning of June. They will just sulk and not grow if planted earlier, but again since I can do them under cover, I can get away with mid May.
Pole beans can't go out earlier than first or second week of June, and since I grow these on a structure, and not under cover, I can't cheat on this date. Cukes get started in pots, then go outside end of May, with me watching the weather and growing them under a cloche if its not warm enough.
My last guaranteed frost date is May 31 so I'm told, but in the 25 years I've been gardening in this location, I've never seen a frost past the first week in May. I do keep an eye on the weather, and protect anything that could be of risk in May. After June, I remove any and all covers.