Cucumber (greenhouse)

Overview

Cucumbers - Curcubita sativus

Greenhouse

Green house cucumbers require high temperatures, very high humidity and a minimum night temperature of 18C/60F to grow successfully. One complaint always associated with cucumbers is bitterness of the fruits. This used to be a problem caused by the pollination of the female flowers by the male flowers. The development of the all-female flowering cultivars of cucumber plants has overcome this problem.

Varieties to choose (as sold by Kings)

How to grow

Sow

Cucumbers are raised from seed. The seed for plants to be grown in a heated greenhouse is sown during February to March and for growing in the unheated greenhouse during April. For quick germination maintain a minimum temperature of 70F/21C. Sow the seed singly in 3”/9cms pots filled with fresh seed compost. Gently push the seed pointed end first into the compost, tap the pot on the bench to settle the compost around the seed, water the pot and place in a propagator until the seed germinates in a week or so.

Growing on

After the seed has germinated the young plants can be removed from the propagator and grown on at a slightly lower temperature of 65F/18C by day and 60F/16C at night. When the roots of the young plant has filled the pot it is time to pot them on them into a 6”/15cm pot filled with fresh potting compost. Wait until the roots have filled this pot and the plants have produced at least four leaves before transplanting them in their final growing positions. Take care not to plant them too deeply to avoid damaging the stems which will cause neck rot. Plant at 2ft/60cm spacings with at least 3ft/90cms between the rows.

Greenhouse cucumbers are grown on the single stem or cordon method. Allow the main stem to grow on before pinching out the growing tip when it has reached ridge bar of the greenhouse. The pinching out encourages sideshoots/laterals to develop. As the laterals grow they produce flowers that in turn produce the cucumbers. The laterals are pinched out a two leaves beyond the fruiting flower. Only allow one fruit per lateral to grow. Remove any flowers or cucumbers as they appear on the main stem.

Aftercare

Water and feed weekly using tomato fertiliser once the fruits start to develop. Damp down the greenhouse morning and afternoon to create a humid atmosphere and spray the plants with plain water several times on hot days. Apply shading to the greenhouse during May if it is a very sunny month. The young cucumber leaves are very sensitive to strong sunlight and are easily scorched by the direct rays of the sun.

How to Harvest

Wait until the cucumber fruit is fully developed all along all of it’s before length before cutting it. Try to harvest in the cool of the early morning or evening. The fruits can be kept fresh overnight by standing them stalk end down in a jug with a little water in it.

Issues

Cucumber mosaic virus causes the plants to have puckered and distorted leaves it is transmitted by aphids. Many common garden weeds are host plants for the virus, it is important to keep the area as weed free as possible (see our weeds list). There are no cures for the virus and all infected plants will have to be destroyed to prevent the virus spreading.

Powdery mildew is a problem caused through dryness at the roots. Water the soil/compost regularly to prevent the plants becoming stressed.

Whitefly and greenfly are the two main pests in the greenhouse use sticky traps to catch the early broods and introduce the biological control Encarsia formosa for the whitefly and Aphidius for the greenfly. Red spider mite can also be a problem if the greenhouse atmosphere is allowed to get too dry. There isn’t a really effective control for red spider mite. Damp down the paths and borders and spray the plants overhead regularly to maintain a buoyant atmosphere.

Neck rot is caused as the result of physical damage to the stem of the cucumber plant that allows a secondary infection to enter through the wounded area. The damaged stem rots and the plant collapses.