By Crow Miller – Growing cucumbers, like European cucumbers, can be a bumper crop in greenhouses. They differ from other types of cucumbers in many ways. The fruits are long, between 14-18 inches, and weigh a pound or more each. The forest green skin is very soft, so many producers wrap each cucumber individually to protect them from bruising and to preserve freshness. The fact that they’re seedless does make them easier to digest, but in reproduction terms, they are hybrids. Many years of plant breeding have resulted in vigorous, high yielding, good tasting fruits.

Even more important for growing cucumbers in a greenhouse, fruit set happens without pollination! Now greenhouse growers incorporate pollinating insects into their community. But for those of you who do not, European cucumbers can be a perfect crop for all garden zones.

Many of the varieties are described as gynoecious (all female flowers). It’s a desirable characteristic because only female flowers develop into fruits. Unfortunately, a small percentage of male flowers will tag along, especially during cool weather conditions. If pollinating insects do inhabit your greenhouse, male flowers must be pinched off to prevent fruit distortion. Distinguishing male from female is very simple. The female will have a small, undeveloped sprout of fruit directly behind the flower. The male flower lacks the swollen carpel and its bloom will be darker than the female bud.

Seeds for European cucumbers can be obtained from most mail order seedhouses, including the top seed companies. There are some facts to consider before ordering: one plant should yield between 20-50 cucumbers; that’s a lot of fruit. And seeds are viable for three years or more under proper storage conditions.

Growing Cucumbers in a Greenhouse: Starting Seeds and Maintaining Temperature

We sow European cucumbers around the first of February when our greenhouse environment is more spring-like. One seed per 3-inch peat pot will provide enough room for early plant development. Keep soil temperature at a consistent 65-70°F. and seeds should germinate in 3-4 days. The soil should be moist but never soggy. Make sure you sow cucumbers in peat pots and not in flats because cucurbit root systems should not be disrupted. Once the seedlings have sprouted with a couple of true leaves showing, plant the entire cucumber, peat pot and all, into the soil beds.

Seedless cucumbers demand arm temperatures for highest yields. At sowing time, soil temperatures should not dip below 68°F.

A seed germinating chamber or box will offer your seeds uniform temperatures for a healthy start. Place a soil thermometer in the area where cucumbers will be set out. When the daily reading indicates 60 degrees F. or higher, transplant your crop. If your soil temperature drops below 60°F, plant growth will stop and general vigor will deteriorate. The recommended spacing is 24 inches between each plant and 5 feet between rows. Organic hydroponic cucumbers may have a denser planting.

This crop will grow best when midday temperatures range between 70-80°F. On clear sunny days, air temperature can rise to the warmer end of the scale. Optimum nighttime temperatures should remain at 65°F, even though some varieties will tolerate a cooler night.

Have your trellis constructed and placed when cucumbers are set out. If it is only one to two large container plantings, train them up a vertical beam with nylon or plastic twine as a leader. Consider that there could be more than 15 pounds of cucumber plant on each string. The vining plant travels quickly and lateral growth requires careful pruning. Pinch off suckers (lateral growth) at the first six leaf axils. The following 8-10 shoots should be trimmed back to one leaf. The remainder can be pruned to two leaves with weaker growth allowing three leaves. Usually plants are grown up to eight feet, and are then trained back down to the ground.

When growing cucumbers, high yields depend upon a balanced diet. European cucumbers require frequent watering and plenty of nitrogen (N). Every 3 or 4 weeks, apply a compost side dressing around the base of each plant. Supplement this feeding schedule with foliar feeding using a micronutrient fish/seaweed sprayed every 14 days. Symptoms of poor nutrition could be yellow leaves, undeveloped or aborted fruit or fruit losing its color. Often you may harvest 5 or 6 cukes per plant at one time.

Growing Cucumbers in a Greenhouse: Concerns About Diseases and Insects

Growing cucumbers in a greenhouse will reduce some of the risk of diseases and insects harming your crop. Of course, a few insects and diseases could put a crimp in your cucumbers’ development. Greenhouse whitefly is a potential pest in spring and summer months. Adults are easy to spot but seeing immature larvae needs the aid of a lens. An integrated control method of trapping adults with sticky orange—yellow boards and a biological control agent can provide tremendous control.

If leaves begin to show a bronze, mottling discoloration, check cucumber plants for the two-spotted spider mite. All stages of the mite’s life cycle are microscopic, but you may notice their webbing between stem and leaf. Safer’s insecticidal soap will check populations.

A common disease affecting European cucumbers is botrytis, a fungal disease that shows as a grayish white on top of the leaves. Botrytis spreads quickly in cool, humid environments.

Powdery mildew is another disease to watch out for. It looks like a white velvet blanket on leaf tops. Powdery mildew affects most plants in the fall when temperatures drop and the relative humidity rises. Mineral fungicides may be applied with discretion at first signs of this fungus problem. Or, better yet, use AQ10 biofungicide. This is a unique biofungicide developed specifically for controlling powdery mildew on vegetables, pome and stone fruit trees, vines and other crops. AQ10 biofungicide is a water-dispersible granule formulation that contains the hyper parasite Ampelomyces quisqualis as its active ingredient.

Of course, natural pesticides for garden pests are always an option.

Growing Cucumbers in a Greenhouse: Training Cucumbers

There are two methods for training vines when growing cucumbers in a greenhouse.

First, triple stem training method. With this method all the suckers are pinched off the developing vine up to the top of the trellis. At the top of the trellis bar, pinch the terminal buds of the main stem and allow three suckers to take over.

The other method is lateral growth training, all suckers are pinched off for the first 4 to 5 fruit sets. Then, the following 8 to 10 suckers are allowed to develop one leaf and one flower. Now pinch tip growth of sucker. All remaining suckers above the 8 to 10 should develop two leaves and flowers. Then pinch remaining growth. Trellis bar is approximately six feet above the ground.

Originally published in the January/February 2000 issue of Countryside & Small Stock Journal and regularly vetted for accuracy.