How to Grow Cucumbers


How to Grow Cucumbers

The taste of a homegrown cucumber is like nothing you can buy! There are many varieties to choose from but there is an important distinction to learn before buying the seeds. There are two main types of cucumbers, greenhouse and outdoor types. Greenhouse cucumbers should, as the name suggests, be grown in a greenhouse because they need a lot of heat to grow well. They tend to produce long smooth cucumbers and do not need pollinating. In fact, any male flowers must be removed as they can cause the fruit to be bitter and full of seeds. However, some greenhouse varieties have been bred to only produce female flowers. There are also some mini ‘snack’ varieties suited for your Harvst Mini Greenhouse. Outdoor cucumbers, also called ‘ridge’ cucumbers, can tolerate lower temperatures and therefore be grown outside. The cucumbers are generally shorter and fatter with a rough, ridged skin. These plants have both male and female flowers and must be pollinated by insects to produce fruit. There are both trailing varieties that can be trained vertically and bush varieties that are more upright and compact.  Some varieties are suitable for both greenhouse and outdoor growing but it is important to not grow a ‘ridge’ type in the greenhouse alongside greenhouse varieties as this can result in cross pollination leading to bitter fruits full of seeds.


When to sow cucumbers depends on their final growing place. February or March is a good time if you intend to grow them in your heated S-Series, and April or May for a greenhouse or outdoors. You can also sow outdoor cucumber seeds directly outdoors in late May or June.

Fill a pot, tray or multi-cell tray with peat-free compost and water it. Sow the seeds at least 5cm apart on their sides (not laying flat) and cover with 1-2 cm of compost. Water again carefully! Putting a plastic dome or cling film on top can help germination but make sure it has air holes for ventilation. Keep the soil evenly moist until the seeds germinate because if they dry out it’s unlikely they will germinate at all. Having said that, be careful not to overwater as cucumber seeds are prone to rot if too wet and cold.

Cucumbers will need 20-26°C to germinate well and normally appear within 7-10 days. Once the seedlings appear, remove the plastic and place in a bright location with 12-16 hrs of light. 20°C is an ideal growing temperature.

Plant care   

Transplant the seedlings to their individual 7-9cm pots when at least one set of true leaves has formed. Do not touch the stem at any point but instead, lift the seedling in its leaf and plant at the same depth as it was. Repot them into slightly larger pots when the roots start to stick out at the bottom, aiming for a 25-30cm pot as the final one. You can also use grow bags or plant into beds or borders. 

You can keep the pot in your Sprout if you have space and have chosen a suitable small variety, or put it outside in summer when the night temperatures are at least above 12-15°C. To acclimatise the plants to outdoor conditions, lift them outside in a sheltered, lightly shaded spot during the day, and put them back in at night. Gradually increase the time outside. Do this for about two weeks before leaving them out all the time.

Water little and often to keep the compost evenly moist and feed every 10-14 days with a balanced liquid fertiliser. Avoid watering on the stem as it can make it rot. Train the main stem up a vertical support like a wire, string or cane or if growing in your Sprout tie it in to grow up on one side. Pinch out the growing tip when it reaches the top of your support structure and pinch out the tip of each flowering side shoot once the fruits begin to develop, but leave two leaves after each fruit. 

Outdoor trailing cucumbers can be left to sprawl on the ground and bush varieties may need staking but not training. Mist the foliage regularly when growing indoors or undercover, as cucumbers need humid conditions to grow well and it will also discourage red spider mites.


Check the seed packet for how big your variety should be. In general, the colour should be evenly green and the fruit firm with a slightly rounded tip. Cucumbers grow very quickly so check them often. If they have started to go yellow, soft or bulbous you have probably missed the boat!  Regular harvesting encourages further fruiting.

Watch out! 

Red spider mites can attack cucumber plants, and are best avoided by regularly misting the plants if grown under cover. Whiteflies can affect the plants by sucking sap and their honeydew causes black sooty mould. Sticky traps can help.

Powdery mildew is often caused by under-watering so can be avoided by keeping the soil evenly moist. Cucumber mosaic virus, which is spread by aphids, can easily be spotted as the leaves develop a yellow mosaic pattern. Unfortunately, there is no cure and affected plants should be destroyed immediately so as not to spread to other plants. Wash your hands before touching another plant! Also, protect young seedlings against slugs and snails.  

Pro Tip

Make sure you spend time researching the perfect variety for your growing space as it can make all the difference. Also remember not to mix outdoor varieties with greenhouse varieties in the same greenhouse!

Nerdy facts

The botanical name of cucumber is Cucumis sativus and it belongs to the gourd family Cucurbitaceae. It consists of 97% water and it seems the term “cool as a cucumber” is linked to its ability to cool the temperature of the blood! In any case, it’s cool to grow cucumbers!

Recommended Varieties

There are lots of different varieties but here are some to choose from.

‘Carmen’ is a great greenhouse variety with straight, glossy, dark green fruit producing only female flowers. It has outstanding disease resistance.

‘Mini Munch’ is an all female greenhouse variety producing small 7cm long delicious cucumbers. It’s a heavy cropper over a long season.

‘Cucino’ produces delicious fruits 10-15cm long. It is best grown in a greenhouse but will crop outdoors in a warm, sunny and sheltered location. 

‘Marketmore’ is a classic reliable outdoor cucumber producing short, dark and ridged fruit. 

‘Bush Champion’ is a compact bush variety, ideal for small spaces.

‘La Diva’ is an all-female flower variety that can be grown in a greenhouse or outdoors. It produces delicious chunky, seedless cucumbers.