Cucumber

Sandy soils are preferred for cucumber production because they warm up faster in the spring. Windbreaks of small grains are sometimes helpful to protect stems of young seedlings from abrading against the soil and from sharp wind-driven sand particles. Soil pH should be between 6.0 and 6.5. See Chapter 1 for a description of types of liming materials and their effect on soil pH, Ca and Mg availability. Cucumber seedlings are very susceptible to residual herbicides. See Chapter 7 for weed management techniques that reduce the use of herbicides.

A ton of cucumbers removes 1.8 to 3 pounds N, 0.6 to 2.0 pounds P2O5, and 3 to 5 pounds K2O from the soil. Consult the table below for plant nutrient recommendations and Chapter 1 for organic sources of these nutrients. For fresh market cucumbers, an additonal 30 pounds N per acre is usually added when the plants have 2 to 4 leaves and vines are just starting to fall over into the rows, but no more than 40 pounds of N or K2O should be applied at any one time. Picking cucumbers are said not to respond to any additional N applications, probably because of the short harvest period.

Potassium and phosphorus are important for good fruit shape, and nitrogen for good fruit color. Low potassium prevents the stem end of the fruit from developing properly. Low phosphorus will give the fruit a dull bronze-green coloration. Low nitrogen will result in light green leaves and fruit. There is some evidence that excessive nitrogen before flowering can delay the onset of flowering, but low N during fruiting can also reduce the number of fruit that develop on the vine.

Planting

Good drainage is important for all cucurbits. Raised 18-inch wide beds on 48-inch centers are often used to provide a level planting surface and good drainage. The height of the bed should be determined by how well the soil drains. Excessively high beds will be more susceptible to water stress, while very low beds may not allow sufficient drainage in 'tight' or organic soils.

Cucumbers are almost always direct seeded. Like most cucurbits, they do not transplant well and transplant costs would be hard to recover. Planting depth is ¸ to 1 inches. Rows are typically 38 to 48 inches apart with 6 to 8 inches between plants. Recommended densities are 15,000 to 25,000 plants per acre for slicers and 20,000 to 35,000 plants per acre for picklers. A density of 35,000 per acre was optimum in terms of yield in North Carolina, although harvest crews performed better at 20,000 to 25,000 plants per acre. High plant populations result in shorter fruit with a lighter color.

Cucumber nutrient recommendations based on soil tests

* 6 inches to side of seed row and 4 inches deep.

Gynoecious lines should be precision planted, if possible, to reduce the need for thinning. Where thinning is necessary, care should be taken with hybrid gynoecious lines not to thin out the monoecious cucumber plants which may be later emerging and less vigorous. Typical planting dates for the coastal plain of North Carolina are mid-to-late April and late July to mid-August.

Successive plantings can be used to extend the harvest season, but timing should be based on heat units for proper separation at harvest. A seven day difference in planting in April may translate into only a one-day difference in harvest in June because the early plantings grow slowly. As a rule of thumb, in the cooler part of the growing season, the next planting should be made when the plants from the previous crop show the first true leaf. In warmer parts of the year, later plantings should be made when 80 percent of the seedlings from the previous planting have emerged.

Water Requirements

Plastic mulch and drip irrigation can improve yields and earliness in cucumbers. On the average, cucumbers need 1 to 2 inches of water every week, with more needed in hot, dry weather. While we think of the South as an area with abundant natural rainfall, in reality, each year unirrigated crops are likely to experience at least one period of water stress. Fruit set and fruit quality are also highly dependent on water availability. Under stress conditions, fruits nearing harvest form bitter-tasting cucurbitacins in the skin near the stem attachment. Some types of cucumbers have a 'bi' or bitter-free gene and never produce cucurbitacins. Unfortunately, these bitter-free cultivars are also less resistant to spider mite damage.

Pollination

Pollination is a critical aspect of cucumber production. Approximately 10 to 20 bee visits are necessary per flower per day for proper fruit shape and size. Poor pollination results in curved (crooked) or short (nubbin) fruits. Since each flower is ope n only one day, it is important to bring hives into the field when 25 percent of the plants are beginning to flower. Bringing bees in earlier is unproductive because they may establish flight patterns to more abundant and attractive food sources such as legumes or wildflowers. Bringing them in later jeopardizes pollination of the first female flowers.

The number of hives necessary depends on many factors, but generally each 20,000 plants need one strong hive containing at least four brood frames. With 35,000 plants per acre, a hive of 35,000 bees will give optimum fruit set. The best way to determine whether the number of bees is adequate is to observe the number of times a given flower is visited. Based on Michigan estimates, during the peak period (10:00 am to 2:00 pm), 11 to 21 bees should visit a sample of 30 flowers in 30 minutes.

When hives are in the field, overhead irrigation and spray treatments should be applied after 5:00 p.m., and sprays should be formulated to reduce drift. Hives should be evenly distributed around the edge of the field, face east and receive morning sun a nd afternoon shade. They should be left in the field 6 to 7 days for once-over harvest or until 4 to 5 days before the last picking for hand harvest. Hives rented for $20 to $40 in 1992.

Table 10.3. Cucumber cultivars with insect and disease resistance