i have 2 cucumbers die on me and bought 2 more all F1 varietybut the last 2 are dying i have done the test where you cur a leef and squeeze it for white milky substance but nothing they are in my greenhouse so are not cold and are fed as instructed

I've one doing well and one that just drooped, someone on here suggested not getting water directly on to the stem, I replaced the droopy one and the new ones doing better ( and the droopy one is back in its pot looking less droopy ?)
I'm now only watering when nessesary and carefully but at the moment even in a greenhouse we are having quite fluctuating temps-- especially at night

many thanks
will try