Plant seeds indoors 5 weeks prior to transplanting (February or early March), using small pots filled with a peat-based potting soil (we use promix BX in our greenhouses). Plant two seeds per pot, and thin out the weaker plants. Cover the seeds with 1cm of soil, and keep the tray in a humity dome. They should germinate in 5-7 days at room temperature. Try to let the soil dry between waterings, and avoid letting the soil sit soaking wet.
Tie up your plants as needed, and cut the side-shoots off as the second leaf has formed. When plants reach the top of your greenhouse, let the main stem go to one side, and preserve a side shoot to go to the other side. Feed every 2 weeks with a vegetable fertiliser.
Problems to watch for:
Root rot: Cucumbers are susceptible to rot, when you transplant, be careful not to disturb the roots.
Powdery Mildew: Prevention is key. Water the soil directly in the morning, and avoid getting water on the leaves. Always ensure there is good air circulation in your greenhouse.
Aphids, whitefly, or other bugs: use beneficial insects, and catch infestations early.