When I've sown my climbing beans too early in the past, by the time I can plant them out after the last frost, so June 1st, they have become so intertwined it takes me hours to untangle them. I think it's towards the end of April before I put mine in and they crop wonderfully.
Courgettes, squashes etc I don't put in before May 1st so they are the perfect size to go out on June 1st.
Cucumbers I will get in quite soon, once I've set up the Jumbo heated propagator in the bedroom
. Tomatoes will go in closer to the end of the month. I have already sown peppers, which take much longer to mature, and don't get drawn so easily.
It will be well into April before my tatties go in, although they've been chitting on a cool windowsill for a few weeks now. Even then I have to be diligent at keeping them earthed up to protect the leaves against frost.
So I judge when to sow by the expected date of the last frosts here, and work out how long things take to grow to reach just the right stage to plant out. I don't always get it right either but that's gardening