At the end of April I potted up into 12" inch pots all my greenhouse stuff, 2 melons, a cucumber, 6 tomato plants, and a courgette. the cucumber and tomatoes are fine, the "gardeners delight" and the "alicante" are about 3' high with tomatoes already set the other 3 tomatoes, "ailsa craig" and the "roma" are about 2' as is the cucumber. The 2 melons have only grown about 2" and the courgette about 5"

Anyone got any thoughts as to why? Day time temps are up in the mid 20sC and don't drop below about 10C at night