Plant seedlings in John Innes no.3 compost in 10” pot or growbags.
Try to maintain the temperature in your greenhouse at a minimum of 60-70°F. Keep the compost moist but never waterlogged, with the air moist and well-ventilated (you can spray the floor to create high humidity).
Train each stem up a vertical wire cane, and pinch out the growing point when the leader reaches the roof. The tip of each side shoot is pinched out at two leaves beyond a female flower. Female flowers have a miniature flower behind them, while male flowers have just a thin stalk. Pinch out tips of flowerless side shoots when 2ft long. Remove all male flowers from ordinary varieties, because the fertilised fruit is bitter (you can also avoid this problem by choosing all-female varieties eliminates this problem. Once the first fruits have started to swell, feed the plants every 2 weeks with a tomato fertiliser.
Cucumbers should be cut when they reach their maximum size. This will depend on variety, but try not to grow huge specimens, or your total crop will be affected. Most types are 6– 8” long, while gherkins are 4”, and apple varieties the size of duck eggs. Use a sharp knife to remove fruits from the stem. Good soil, proper care and continuous picking should provide you with lots of cucumbers until the end of September.