Greenhouse Cucumber Telegraph Greenhouse Cucumber Telegraph. The original and most popular greenhouse cucumber producing huge crops of long dark English Type cucumbers of perfect shape and excellent mild flavour. Produces male and female flowers. Must be trellised to achieve perfect shaped fruits. Cultivation Advice Sow under cover (protected / heated) from Mid spring, 3-4 seeds 1in deep in a 3in pot in good compost, and thin later to the best one or two plants per clump. (These will not germinate in cold / damp conditions, use a propergator or warm windowsill) Transplant no later than 3 weeks after seeding as cucumbers have a tap root that can be easily damaged. Cucumbers germinate and grow best when summer really gets going, this variety under glass. To avoid bitterness, keep plants evenly moist at all times. Train on a trellis to achieve straight fruits. Keep them picked and they’ll keep producing.