Cucumber, Muskmelon, and Watermelon

Introduction

Cucumbers and muskmelons (genus Cucumis) and watermelons (genus Citrullus) are related crops that have similar cultural requirements. All three are tender, warm season vegetables that will not tolerate chilling or soil temperatures below 55°F. 

Types and Varieties

Cucumber types include pickling (short, with spines), slicing (long, with spines), Asias and European (long, slender, and seedless), and beit alpha (tender, mild tasing, and spineless). Muskmelons (a.k.a. cantaloupes) have orange, musky flesh, and are the most common type of melon grown in New England. Specialty melons with white or green flesh include casaba, galia, crenshaw, Asian, and honeydew types. Watermelons exhibit a range of flesh colors (red, yellow, orange) and both seeded and seedless varieties are available.

The number in parentheses is the approximate number of days to maturity from seeding.

Resistant or tolerant to: A: Anthracnose; ALS: Angular Leaf Spot, DM: Downy Mildew (current races only), CMV: Cucumber Mosaic Virus, FW: Fusarium Wilt, PM: Powdery Mildew, PV: Potyviruses, S: Scab, WMV: Watermelon Mosiac Virus, ZYMV: Zucchini Yellow Mosaic Virus

OP: open-pollinated, P: Parthenocarpic (sets fruit without pollination)

Soil Fertility

Soils that warm up quickly in the spring are preferred over heavier soils that remain cool. Muskmelon should be grown on very well-drained soil for optimum quality. Raised beds provide additional benefits. The soil should be fertile and high in organic matter. On sandy soils, irrigation is necessary. In non-irrigated fields, apply the lower rates of fertilizer recommended.

Apply lime according to soil test to maintain soil pH at 6.0-6.8. Watermelon can tolerate pH as low as 5.5. If the fertilizer cannot be banded at planting, add the band fertilizer amount to preplant broadcast application. If growing plants on plastic mulch, nitrogen can be applied through trickle or overhead irrigation or sidedressed along the edge of the plastic mulch. Nitrogen under the plastic mulch is protected from leaching. Foliar feeding rate is 8-10 lb actual N (4-5 lb urea) per acre. Wet foliage is conducive to disease development, so avoid foliar feeding after the 5 leaf stage.

If using transplants, use of a liquid starter fertilizer at planting time is beneficial. This is especially true with cool soil conditions because P uptake by plants is slow in colder soils. Although the specific analysis of the product is not critical, starter fertilizers usually contain higher amounts of P. Follow the recommended mixing rates on the product.  

Planting

Cucumbers may be direct seeded or transplanted. Because of the long season required for muskmelon and watermelon, transplants are used. Transplants are preferred for early crops. The plants should be about 3 weeks old, with just 1-2 true leaves, at transplanting time. Older transplants that have begun to run are difficult to handle and suffer greater transplant shock.

Recommended spacing for slicing cucumbers, muskmelons and watermelons is 2' between plants and 6' between rows. Pickling cucumbers should be direct-seeded at 6-8" between plants and 3-6' between rows, depending on the cultivar. Most cultivars should be planted at 3' between rows.

Seedless watermelons require special growing conditions. Seedless cultivars are sterile because they are triploid, and this negatively affects their germination ability. They require high temperatures (85-95°F) during germination, and excess soil moisture should be avoided. To ensure fruit set, a diploid (seeded) vaitety or a “pollenizer” variety must be planted among seedless watermelons in a ratio of at least 1 for every 3 seedless plants. Growers have moved to using “pollenizer” instead of diploid varieties because they are bred to produce a large number of male flowers with viable pollen, are less competitive and take up less field space than diploids varieties.  Different pollinizer configurations can be used successfully; however, placing pollenizers in-row with seedless varieties at like spacing or interplanting pollinizers between every 3rd and 4th seedless plant tends to promote better yields compared to dedicating separate rows of pollinizers. The latter strategy is preferred if growing triploid (seedless) and diploid (seeded) varieties within the same field. 

In some growing seasons, vine crops that have recently been transplanted or have just germinated suddenly wilt and die. Most often, this situation occurs just following a period of 4-5 days of rainy or cloudy weather. Without sunshine, soil temperatures drop below 55-60°F. At these soil temperatures the plant roots cannot absorb water from the soil. Consequently, when the sun does reappear, water transpires from the leaves much more rapidly than the roots absorb water, resulting in sudden wilting and death. There is no control for this problem, except to attempt to manipulate planting around weather forecasts. Earlier planting dates increase the likelihood of this problem. Transplants can also be injured by excessive heat, especially when planted into black plastic mulch when temperatures are high and air pockets under the mulch get superheated, and/or when stems touch black plastic and are scorched. White-on-black plastic, which does not absorb as much heat, can be used for late-season cucurbits to avoid this outcome.

Field Culture

Early and total yields are increased with black plastic mulch. For summer plantings when day time temperatures are 85°F or greater, more growers are using white-on-black plastic mulch to avoid high soil temperatures that develop under black plastic. Before the plastic is laid, be sure the soil is fertilized and the soil surface is smooth. The plastic should fit snugly against the surface. Do not lay plastic on dry soil; either irrigate or wait for rain to ensure the soil is moist prior to laying the mulch. In conjunction with plastic mulching, using hoops and spunbonded row covers early in the season will provide earlier and higher yields, while also helping to control insects such as striped cucumber beetle. Apply the covers at the time of planting and leave on until flowers are present to allow for pollination by bees. These crops can withstand high temperatures under the covers. A sufficient number of pollinating insects should be present to ensure adequate fruit set in cucumber and melons. One strong hive of honeybees per acre as flowers just begin to open is recommended.

Cucumber Protected Culture

For greenhouse or high tunnel production, growers may choose to use varieties that are parthenocarpic, meaning that they set fruit without pollination. Other types can be grown, but will require pollination which could be prevented or limited by the structure and other exclusion techniques employed for pest management. However, if parthenocarpic varieties are pollinated, fruit quality is reduced. In more open high tunnel structures where pollinators are likely to visit, it may be better to avoid parthenocarpic varieties and use gynoecious varieties, which produce mostly female flowers. 
 
In protected systems, cucumbers are best trellised to use space efficiently, promote an easier harvest and encourage airflow. This can be done by using netting (commonly used with unpruned field types) or by wrapping or clipping to strings (similar to high tunnel tomato production). Cucumbers can be pruned back to one or two leaders in these systems and subsequent pruning is needed on a regular basis to remove future lateral branches, known as suckers. Cucumbers are vigorous plants and often exceed the height of the trellis system.

Growers have managed this by heading the top of the plant above a node and allowing two lateral branches to develop and grow down in an “umbrella” system. Other growers simply allow the single or double leaders to hang and grow back down. A third system involves lowering and leaning cucumbers just like indoor tomato plants.

Protected culture cucumbers have been grown successfully with various spacings. A common spacing is 18-24” in-row spacing on beds with single rows. However, single rows using 12” in-row spacing and double rows using staggered 24” spacing are both used. Between-row spacing should be 4-6'. Match spacing with needs, varieties, pruning, and management systems. 

Harvest and Storage

Cucumber. Harvest on a regular basis (3-4 times per week) to obtain a maximum number of fruits. Cucumbers are sensitive to chilling injury; optimum storage temperature is 50-55°F.  

Muskmelon. Melons change color as they ripen, generally taking on a yellow hue. Harvest cantaloupe and galia-types from half- to full-slip, when the melon receptacle becomes corky and a slight push of the stem will cause the melon to separate from the vine. At half-slip they are less ripe and shelf life is increased, but some flavor may be compromised. 

Only well-netted cantaloupes should be harvested; fruits with poor netting have generally been stunted in growth and lack good flavor. Other muskmelon-types require different harvesting techniques which can be specific to individual varieties. Generally, honeydews lose their fuzzy feel and must be cut from the vine at peak ripeness. Canary and crenshaw melons are harvested at forced-slip.  Hold muskmelons for 1-2 days at 70°F for final ripening; for longer periods of storage, maintain a temperature of 50-55°F. Long shelf life (LSL) or ‘harper’ style melons have been bred to hold for controlled pick harvests. 

Watermelon. Varieties vary in maturity indicators. The proper time to harvest must be learned by experience (and perhaps by wasting a few fruits). Dried (brown) tendrils and ground spots are two generally reliable indicators of ripeness. When the tendril on the vine at the juncture of the fruit stem turns brown, the watermelon is close to maturity. A bright yellow ground spot on the underside of the fruit also indicates maturity. The thumping method to identify ripe melons can work, after some experience is developed. Store watermelons at 50-55°F.