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Cucumbers (Cucumis sativus) are grown in home gardens in all regions of Minnesota. They are typically eaten raw in salads or pickled. Like other “vine crops” such as squash, melons, and pumpkins, cucumbers grow most vigorously and produce the most fruit in warm weather. Long taproots and branching surface roots enable cucumber plants to access soil moisture even in dry weather, however vine crops are heavy water feeders and soil moisture should be constantly monitored. Some varieties form long vines that may ramble or be trellised; others are bush types that fit more easily into a small garden. Cucumber plants bear separate male and female flowers on the same plant (monoecious), and pollen must be transferred from the male flowers to the female flowers by an insect. Male flowers usually appear first, each attached to the plant by a slender pedicel, or stem. Female flowers are attached close to the main vine, and between the flower and the vine is a small round ovary, the unfertilized fruit. Cucumber flowers are typically pollinated by bees.
Some newer varieties of cucumber are parthenocarpic, meaning that the plants will set fruit that develops normally, even if the female flowers are not pollinated. These fruits will be seedless or nearly so. Other varieties are “all female” or gynoecious, meaning that they bear only female flowers, each of which can produce a fruit. These varieties have high potential yield. All female varieties must be grown with another cucumber variety having traditional flowering habit to provide pollen.
Cucumber seeds will not germinate in cold soil, nor will plants started indoors and set out into cold soil grow very well. Further, the taproot of cucumbers and other vine crops must not be damaged in transplanting, so plants started indoors must be transplanted carefully, before the plant begins to outgrow its container. Since the plants cannot survive freezing temperatures, plan to set the plants out after the last frost date. Start seeds indoors no more than four weeks before the last frost date, and start the seeds in peat pots that can be planted directly into the soil.
Direct-seeding is the preferred method for starting cucumbers. Use a soil thermometer and sow seeds after the last frost date, once soil has warmed to 70° F at the 1-inch depth. In most of Minnesota, this will be sometime in late May.
Earlier planting is possible with the use of black plastic mulch, which raises soil temperature, along with spun row covers, which raise air temperature around the plants and protect them from cold nights. Apply black mulch to the soil once the soil is prepared in spring. The black color will absorb heat from the sun and warm the soil faster than if it were uncovered. Cut holes or slits in the mulch, and plant the seeds as above. After the seedlings have emerged, position the row covers over the plants, securing the edges with soil or staples. Row covers exclude both pests and beneficial insects needed for pollination, so they must be removed from the plants once flowering begins, unless the variety is parthenocarpic.
Sow seeds about ½ inch deep. For vining types that will be allowed to spread out in the garden, seeds should be sown two inches apart. Allow about two or three feet of space on either side of the row for the vines to spread. After emergence, thin seedlings to stand 8 to 12 inches apart. The vines may also be trained to climb a three- to four-foot trellis, allowing garden rows to be spaced more closely, and producing perfectly straight fruit.
A “hill” of three or four seeds sown close together is another way to plant cucumbers in the garden. Allow five to sex feet between hills. Bush types, with very short vines, can be planted in closely-spaced hills, or in closely-spaced rows, with only two to three feet between rows or hills.
For best yield and quality, the optimum soil pH range for vine crops is between 6 and 6.5, which is slightly acidic. However, most gardeners, even those with neutral or slightly basic ("alkaline") soils can successfully grow cucumbers. Have your soil tested to determine its pH and whether you need to amend it.
Nearly all garden soils benefit from the incorporation of well-rotted manure or compost before planting. Adding this organic matter improves both heavy clay soils and lighter sandy soils. Before adding any compost, manure, or fertilizer, a soil test should be performed. Without a test, it is impossible to know how much or which type of fertilizer to apply.
In midseason you should apply a side-dressing of nitrogen fertilizer such as ½ cup 46-0-0 or 1 cup 27-3-3 for each 25 feet of row. If you incorporated manure or compost, additional fertilizer applications may be reduced or eliminated, depending on how much organic matter you apply. Do not use "Weed and Feed" type fertilizers on vegetables. They contain weed killers that will kill vegetable plants.
Continuous use of high phosphorus fertilizer such as 10-10-10 or 15-30-15, or high rates of manure or manure compost results in phosphorus buildup in the soil. Although phosphate fertilizer applied to soil is bound tightly and resistant to movement in the soil, some runoff may occur. It can then become a major pollution concern in our lakes, rivers and streams. High levels of phosphorus support over-production of algae, which causes significant reduction in water quality (see Preventing Pollution Problems from Lawn and Garden Fertilizers). If your soil tests high in phosphorus, use a low phosphorus (such as 32-3-10, 27-3-3, or 25-3-12) or no phosphorus (such as 30-0-10 or 24-0-15) fertilizer.
Proper watering will enhance good production. Vine crops need at least one inch of water from rainfall or irrigation each week during the growing season. Always soak the soil thoroughly when watering. There is little or no value in a light watering that only wets the surface of the soil. On most soils, watering once a week is sufficient. Sandy soils should be watered more frequently but with lower amounts applied at any one time.
Frequent, shallow cultivation will kill weeds before they become a problem. Many roots of vine crops are close to the surface of the soil, so it is important not to cultivate too deeply or too close to the plants. Cultivate just deep enough to cut the weeds off below the surface of the soil. Continue cultivating as long as you can do so without injuring the vines, usually when the vines begin to spread between the rows. When cultivation is no longer possible, pull the large weeds by hand.
Pick cucumbers when they reach the size you prefer. For pickles, try to harvest at a uniform size. Pickling cucumbers often have very good flavor for salads as well. Slicers or salad cucumbers can be harvested at any size, but before they are over-large, with large seeds and yellowish skins.
If very large cucumbers are left on the vine, plant yield will decline. Harvest often, but be careful not to disturb the vine, as they often send out new roots from joints in the vine. Disturbing the vine can break these roots. Do not pick fruit when the vines are wet, because of the danger of spreading diseases.
For assistance in diagnosing unknown problems visit ‘What’s wrong with my plant?’.
Poor fruit set could be due to inadequate pollination. Pollination may be hindered by cold, rain, or cloudy weather.
Bitterness in cucumbers is sometimes a problem. Typically, fruits are more bitter closer to the skin, and bitterest at the blossom end. Concentrations of the bitter compound, cucurbitacin, vary among varieties, and there are some genuinely non-bitter varieties available to home gardeners. Bitter varieties are more attractive to cucumber beetles, so planting non-bitter varieties has the benefit of lessening pest pressure.
There are several insect pests you may encounter on your cucumbers. Squash vine borers attack and bore into the vines killing the plant. Squash bugs feed on plant sap and can be injurious, especially to young plants. Striped cucumber beetles damage plants by eating leaves as well as stems and fruit. They are also a potential vector of bacterial wilt.
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