Fertilizers ?

Hello

I was wondering which fertilizer to use for my cucumbers, I have a special tomatoe fertilizer ( 12-10-20+2 with magnesium) and another type : 18-9-20.
Which would be better for the cucumber and when/how often should I feed them ?
At the moment the plants are about a foot high,big leaves , good colour but no flowers yet...(they are a F1 variety and grown outdoors in containers)

 

I've always used tomato fertilizer on mine, a weak solution on every 2nd watering. Not sure if this is best but the only problem i've had so far is having more cucumbers than i can use/give away!