Text & photo: Christine Wiemann

 

Cucumbers are always a hit. We love to cultivate cucumbers in the greenhouse when it is summer. Sometimes you may run into trouble with the cultivation, where the plants die or are attacked by plant diseases. Or you may be overwhelmed by a large amount of growth and become unsure of how to prune the plant. In this article you will get all the knowledge you need to grow the prettiest cucumbers in the neighbourhood.  

Cucumber (Cucumis) is a genus with about 50 species. Cucumber Cucumis sativus as we know it, is one of these species. Cucumbers are related to melons for instance. Cucumbers have been cultivated for more than 3.000 years. It is originally from India. It is said to be introduced to Europe by either the Greeks or the Romans.

 

The wild cucumber

The original wild cucumber plant, which our modern cucumber is bred from, is vastly different from those we know today. The wild cucumber had originally spikes, tasted bitter and was not pleasant to eat. The spikes and the bitterness are almost gone with the one we cultivate today. This is for example the case with the modern F1 sorts. But with some sorts there are still hints of spikes. Some sorts may also get a bit bitter taste especially if they are not harvested in time. Although buying F1 seeds or plants, you are almost certain to not get a bitter taste or funny looking crops.

Late pre-germination

Cucumbers are one of the last plants you should pre-germinate in the windowsill in April. Cucumbers love the heat. English cucumbers and Picolino F1 are meant to be cultivated in the greenhouse. The small Melothria is in botanically terms not even a cucumber but a different botanical species.

A rule of thumb is that you sow 3 to 4 weeks before transplanting. When the seed has started germinating, the plant will soon begin to grow.

The temperature during germination should be about 20 degrees Celsius. The seed should not be covered with more than three times the soil compared to the size of the seed. That is approx. 0,5-1 inch of soil, and always use potting soil when pre-germinating.

 

The small plant 

After pre-germination the plant needs as much light as possible. Temperatures lower than 15 degrees Celsius are not ideal for cucumber plants. Especially not while the plant is still young. If you want to be safe, wait to transplant the cucumber until the start of June. Climate change may have made it possible to transplant sooner, so if you did it earlier that should be fine too.

Many greenhouse cultivators have lost their cucumber plants because they were too enthusiastic and transplanted their plants too soon to the greenhouse.

 

Transplanting in the greenhouse 

Tomatoes can be planted quite deeply in the growbag, but this is not the case with cucumbers. Cucumbers are delicate plants and are more vulnerable to fungus diseases. Therefore, the cucumber should not be planted too deep. It is especially the base of the plant that is vulnerable, and the stem should not be covered with soil.

 

Temperatures in the greenhouse

The ideal temperature for cucumbers to grow is between 28-30 degrees Celsius, but to get a large amount of cucumbers, then 20-22 degrees during the day and 18-19 degrees at night is best. The temperature of the soil, on the other hand, should not be lower than 15 degrees. If it is lower than this, you risk that the plant growth stops.

 

Light in the greenhouse

When the cucumber is no longer a young plant, it can endure more sunlight in the southern facing part of the greenhouse. The plant will then grow large leaves that can provide shade for tomatoes or other plants that do not need the direct sunlight.

 

Caring for your plants 

If this is your first time cultivating cucumbers in the greenhouse, then you may be surprised of the enormous growth and lushness in your greenhouse.

Once the cucumber plants are settled in, the plant will start to grow. Cucumbers grow uncontrollably if it is not pruned. Try to find a balance between growth of shoots and the growth of fruits. If the plant only grows a lot of cucumbers, then it will take up all the strength, and the further growth will stop.

Male and female flowers

Some cucumber sorts produce male and female flowers. Male flowers should be removed instantly and female flowers can be recognized by seeing whether a small cucumber is growing underneath the flower. If there are flowers blooming with no fruit, remove the flower. A lot of F1-hybrids only get female flowers, making it a lot easier since no flowers need to be removed.

The first fruits and pruning

The first cucumbers grow from the main stem, and it is tempting to let them stay. What most people do is to remove all flowers on the main stem and let every other side shoot stay, but prune it after every other leave pair. Remove the shoot at the top of the main stem when the plant gets 2 metres tall. When the shoot at the top is removed, the plant will start growing new side shoots. These side shoots will grow their own side shoots which in the end will get you a lot of cucumbers. For this to succeed, you need to tie up the plant. You can for example use one of these options: wirekit or plant spiral.

 

 

Create a healthy climate

When summer comes, it is time to remove all the leaves and shoots from the bottom and half a meter up on the main stem. This way your greenhouse will have better air circulation.

 

Diseases and pests

The most important cucumber disease is mildew which is a fungus disease. The leaves of the plant will look like they have been powdered with flour. Eventually, the leaves turn yellow and wilt. The mildew can only survive on living plants. You can prevent the fungus and reduce its growing by keeping a high humidity in the greenhouse. Shower your plants once a day including under the leaves. You can also get mildew resistant cucumbers sorts.

Spider mites are a common pest on cucumber plants. They make a web just like spiders. The spider mites will be under the leaves. And once again water works wonders. Spray with clean water as often as possible. You can also get insecticides to get rid of the spider mites.

 

9 tips

• Start pre-germinating in the end of April
• Choose F1 sorts to avoid bitter taste
• Wait transplanting until the beginning of June
• Avoid planting the seed too deep and keep the base dry
• Shower the plant daily with water (also underneath the leaves)
• Cucumbers thrive in growbags, capillary boxes and in pots
• Remember to tie up the plant
• Don’t let the fruits become too big
• Share with your neighbour