Popular garden cucurbits include cucumbers, many melons (including watermelon), summer squash (including zucchini), winter squash (including pumpkin), and some gourds.
Cucurbits prefer loose, loamy, fertile soil with good drainage. Some gourds, mostly inedible varieties, and some other garden-cucurbit varieties can be drought-tolerant, but the vast majority of edible cucurbits need consistent soil moisture to maximize growth and yields. Most cucurbits suffer and become highly stressed in dry soils, and are also prone to diseases in wet soils or if overwatered. Cucurbits may suffer or require more-frequent watering in sandy or other soils that dry out quickly.
Cucurbits need good drainage and may benefit from being planted in raised beds or mounds that are raised several inches to a foot or more above grade. In loose and sandy soils, cucumbers may benefit from being planted in a shallow hollow or depression with mulch to retain soil moisture. The hollow can be filled to provide the extra water cucurbits may need in sandy soils while avoiding runoff. Keep mulch a few inches away from cucurbit stems to avoid encouraging rot.
Cucurbit seeds may rot if kept overly wet when germinating. Plant cucurbit seeds directly into moist, pre-irregated soil. As a general rule, wait to water germinating cucurbit seeds again until the soil surface is dry down to about 1/8 to 1/4 inch. Larger cucurbit seeds, such as those for large pumpkins and large winter squash, may need extra water to germinate well.
Water cucurbits at soil level. Allow soil surface around seedlings to dry between waterings. Cucurbit leaves as should be kept as dry as possible at all times. Avoid watering with sprinklers or wetting foliage, which encourages mildew that may reduce yields or even kill plants. Many a squash or melon harvest has been cut short because of sprinkler overspray from a nearby lawn. Walking or working near cucubit plants when they are wet after rain or from overhead irrigation may encourage the spread of foliar diseases.
The best method for watering cucurbits is generally drip irrigation, which allows for deep infiltration of water over time. As much as possible, keep cucurbit leaves entirely dry, particularly after plants begin to bloom and produce fruits. Consider installing drip irrigation before planting, which can save hassle and damage to plants later on. With drip tubing already in place, it’s easy to plant seeds or pre-germinated seeds near individual drip emitters. Tubing may need to be adjusted or moved from time to time as plants establish and for some varieties eventually become large.
Avoid applying strong streams of water that erode soil and expose roots, which may stress plants, encourage pests and diseases, and reduce yield.
Water progressively more deeply and less frequently as plants mature to encourage deeper rooting. Young cucurbit plants should be watered to a depth of several inches, while larger, mature plants should be watered slowly and for periods of 20 minutes to an hour or longer to wet at least the top 12 to 18 inches of soil. In loose, deep, fertile soil, many cucurbits may develop roots to a depth of 4 feet or more. Deep watering is particularly important in hot-summer areas; plants with deep roots will be more tolerant of summer heat, more productive, less prone to pests and diseases, and less likely to wilt during hot weather.
Mastery in watering cucurbits involves spacing drip emitters effectively and strategic, careful, infrequent watering so that soil surface is dry most of the time but with consistent moisture lower in soil for plant roots. Moist upper soil may create humid conditions aboveground, which encourages mildews and foliar diseases in cucurbits. This is a less-serious issue than wetting leaves with sprinklers or overhead watering, but over weeks and months can make a significant difference in plant longevity, vigor, and yield.
Frequency of watering may vary significantly for cucurbits depending upon depth of root system, plant maturity, soil texture, ambient temperatures, type and variety of cucurbit, and other factors. Established cucurbit plants may go 1 to 3 weeks or longer between deep waterings in cool weather. A healthy cucurbit plant with a reasonably deep root system may go 3 to 7 days or longer between waterings in warm weather. In poor or sandy soils, or if root systems are shallow, cucurbits may need watering every day or every other day during warm-to-hot weather.
To test moisture by hand in loose or sandy soils, press a finger into the soil at the edge or outside of a cucurbit’s root zone. If soil is moist and sticks to your finger, water is generally adequate. For dense and clay soils, use a tool such as a screwdriver or thin stiff rod. If the tool can be pushed easily into soil, water should be adequate; texture and friction will change as the tool encounters drier soil.
Water penetration in soil can generally be evaluated by pressing a long screwdriver or thin metal rod into soil and noticing when soil resistance changes as dry soil is reached. A shovel can also be pressed carefully into the soil outside or at the edge of an established plant’s root system.
Sufficient, even watering is especially important for cucurbits while they are flowering and fruiting. Water-stress while fruiting may increase bitterness or toughness, affect texture or eating quality, or otherwise reduce quality of cucurbit fruits.
At high temperatures, the large leaves of many cucurbits are prone to wilting regardless of how much water is available in the soil, as they transpire faster than their roots can uptake water. Any wilting is undesirable and stressful to plants, but can be difficult to prevent with cucurbits during hot weather. GardenZeus recommends providing shade during hot afternoons, and if wilting becomes severe or repetitive, trimming portions of large leaves or removing leaves if cucurbit plants wilt in hot weather despite being well-watered. Judicious leaf-thinning may reduce short-term yield but also will reduce wilting stress to the plant, which may allow it to survive, avoid disease or pest infestation, and produce a larger yield over time. If removing cucurbit leaves, avoid removing leaves that are shading fruit, as the fruits of most cucurbits are subject to sunscald if exposed to too much sun, especially during hot weather.