Cucumber

Growth habits. Cucumber vines can be trained on trellises to save space and improve yield and fruit quality. Procedures for growing on trellises are described at the end of this chapter, but the high cost of trellising makes commercial production by this method uneconomical in most cases. Greenhouse cucumbers must be trellised, however, because the long fruit bend if they rest on the ground.

Genetics. Cucumbers cannot cross with any other cucurbits, although popular lore often attributes off-shapes or flavors to such crossings.

Flowering types. Older, as well as many current cucumber cultivars, have a monoecious flowering habit, producing separate staminate and pistillate flowers on the same plant. Although the terminology is not botanically correct, staminate flowers ar e often referred to as male flowers and pistillate as female. This usage is followed here for the sake of simplicity. Monoecious cultivars first produce clusters of five male flowers at the leaf nodes on the main stem. Subsequently, the plant produces both male and female flowers.

Most current hybrids are gynoecious (all female flowers). Gynoecious hybrids are widely used because they are generally earlier and more productive. The term all-female is somewhat of a misnomer, however, as 5 percent of the flowers are male under most conditions. In sensitive gynoecious cultivars, production of male flowers is promoted by the long days, high temperatures and high light of early summer. Production of male flowers also increases with high fruit load and other stresses on the plant. Production of female flowers is promoted by the short days, low temperatures and low light conditions of fall.

Pollination in gynoecious crops is ensured by blending seed of a monoecious cultivar (pollenizer) with seed of the gynoecious hybrid. Typical ratios are 88 percent gynoecious to 12 percent monoecious. Pollenizer seed is often dyed a different color to distinguish it from that of the gynoecious hybrid. It is difficult to recognize pollenizer seedlings after emergence in the field. Removing 'different looking' seedlings during thinning may remove the pollenizer.

When cucumbers set fruit without pollination, the resulting fruit are called 'seedless', although the fruit often contain soft, white seed coats. Such parthenocarpic fruit set occurs naturally under the low-light, cool-night growing conditions, and short days of fall. Older plants of squash and cucumbers can also produce 'super' ovaries which set fruit parthenocarpically. Greenhouse cucumbers are naturally parthenocarpic. If pollinated accidentally, fruit of these cultivars may be deformed by greater growth in the pollinated area.

Climatic Requirements

To ensure satisfactory stand establishment, soil temperatures should be at least 60 degrees F. The higher the soil temperature, the more rapidly seedlings emerge and the less vulnerable they are to seed corn maggots and damping-off diseases. At 60 degrees F, 9 to 16 days are required for seedlings to emerge. At 70 degrees F, only 5 to 6 days are required. Even after emergence cucumbers remain sensitive to cold temperatures. Seeds should always be planted late enough to avoid frosts. Exposure to cool conditions will slow growth even if temperatures remain above freezing. The optimum daily average air temperature is 65 to 75 degrees F. Slow-growing seedlings are vulnerable to flea beetles whose chewing significantly reduces leaf area of young plants. Very high temperatures during flowering decrease pollen viability, however.