Growing melons (cantaloupe, watermelon, honeydew) in Minnesota home gardens
Melons are members of the cucurbit family, which includes pumpkins, zucchini, cucumbers, summer squash and winter squash. Being closely related, melons have similar growth requirements, however they will not cross-pollinate with cucumbers, squash or pumpkins.
Melon quality is a function of the sugar content of the fruit. High sugar content is achieved by avoiding all stress during the growing season. Stress comes from foliar diseases, insect pests, weeds, poor nutrition, and excesses or lack of water.
Melons prefer hot, sunny locations with fertile, well drained soils, and can be either transplanted or direct seeded. Transplanting can add 2 to 4 weeks to the growing season, but melons are particularly sensitive to root disturbance and growth will be retarded if transplants are not properly managed.
Melon seeds germinate optimally between 70 and 90 degrees F but can be sown when the soil temperature is above 65 degrees F. Planting in cooler soil favors soil borne root diseases which can decimate or stunt melons which are cold intolerant. An average planting date is a week to 10 days before the historic frost free date. This is approximately May 20 in Minnesota but will vary depending on your latitude.
Plant the seeds ½ to 1 inch deep. Plant 2 to 3 seeds in groups 18 to 24 inches apart within the row and later thin to the best plant per group. Space rows 5 to 6 feet apart.
Sow seed indoors at the end of April, about 2 to 4 weeks prior to the transplant date. Transplants should have 2-3 mature leaves and a well developed root system when they are moved into the garden. Plant the seeds in peat pots or other biodegradable containers that can be placed directly into garden soils. This will help avoid root disturbance and damage. Damaged roots in seedling transplants slow establishment and growth. Plant the potted seedlings 2 feet apart through plastic mulch for early maturity.
The use of plastic tunnels and fabric covers can protect seedlings and transplants from cool air temperatures and early insect pests. Covers can increase temperature around the plant and will stop pollinating insects from reaching the flowers. Remove covers once fear of frost has passed to avoid high temperature plant injury and to allow bees and other pollinators easy access to the flowers.
Cantaloupe plants can be grown in small gardens by training the plant to a fence or trellis. After the fruits begin to enlarge they will need support or the fruit weight may damage the vines!
Soil pH and fertility
Muskmelons grow best on well-drained, sandy loam soils with a pH level between 6.0 and 6.5. Soils with a pH less than 6.0 will produce plants with yellowed foliage and fewer perfect flowers. If drainage is a problem, plant in 6 to 8 inch high beds. Before adding any compost, manure, or fertilizer, have your soil tested (see Understanding Your Soil Test Report) to determine your soil’s pH and whether it should be amended.
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.
You can also improve both heavy clay soils and lighter sandy soils by adding organic matter. Addition of manure or compost is beneficial for vine crops and improves soil structure. Plow or till well-rotted manure and fertilizer into the soil before planting. If you use 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.
Timely and appropriate applications of fertilizer can make a significant difference in the quality and quantity of fruit and may promote earlier harvests.
Plastic mulch warms the soil, conserves water, helps to control weeds, allows earlier planting and maturity, and reduces ground rot of the fruit. The use of transplants with plastic mulch generally results in harvests that begin 7 to 14 days earlier as compared to growing melons on bare ground. To get the benefits of plastic mulch, proper installation is critical. First lay drip irrigation or a soaker hose on the soil. Be sure to offset the drip tape 2 to 3 inches from the center of the bed. Further maximize the benefits of plastic mulch by installing it over raised beds. Lay the plastic mulch during the hottest part of the day and make sure that the mulch is stretched tight over the soil without any wrinkles. Lay the plastic, secure the edges with soil on each side of the raised bed, and cut holes for the seeds or transplants. When using plastic mulches and row covers, seeds or plants can be set out about 2 weeks before the last frost date.
Organic mulches like woodchips or straw can also be used when growing melons, but do not apply organic mulches until soils are warmer than 75°F.
Frequent, shallow cultivation will kill weeds before they become a problem. The roots of melons 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 deeply 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 large weeds by hand.
Water deeply and infrequently, 1-2 inches per week. Use drip irrigation if possible. Mulch around the plant will conserve soil moisture and reduce weed growth. 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. Reduce watering amount as the fruits ripen to improve flavor. Even watering is extremely important especially in the last 2 weeks of growth. Excessive watering at this stage can cause the fruits to split.
Pollination and flower types
Cucumbers, squash, pumpkin and watermelon have separate male and female flowers. Cantaloupe (muskmelon) has two flower types, male flowers and complete flowers (having both male and female parts). Cantaloupe flowers have a pollination window of one day. Pollen must be transferred from the male flower to the female flower on this day for seed set and fruit development. Fruit size and shape are related to the number of seeds set. Poorly pollinated flowers either abort or produce misshapen fruit.
Harvest and storage
Cantaloupe requires 35-45 days to mature from flowering, depending on the temperature. As the fruit matures the skin surface netting gets coarse and rough, the background color of the fruit turns from green to yellow,the surface color becomes dull, and the tendrils near the fruit (which look like curly strings) on the stem dry and turn brown.
Harvest the fruits by twisting the fruit at which point it will separate from the vine. Do not wait for the melons to separate from the vine on their own. At full maturity and peak flavor the stem breaks (slips) away from the vine easily. This stage is called “full slip.” Commercial melons are harvested at "1/2 to 3/4 slip" to reduce shipping damage. This removes the fruit before it has reached maximum sugar content, and sugar content will not increase after harvest. This opportunity to harvest at maximum ripeness is one of the advantages of growing your own melons. Pick melons as they ripen as they will not all ripen at the same time. Cantaloupe will store for 1-2 weeks if held at 45-50°F.
Identifying ripe watermelon and honeydew melons is more difficult as most of these fruit types do not slip from the vine. Use a combination of indicators to determine ripeness. Look for (1). tendrils near the fruit stem to become brown and dry; (2) the fruit surface to become rough to the touch and the fruit color to become dull; (3) the bottom of the watermelon (where it lies on the soil) to change from a light green to a yellowish color. Assuring ripe honeydew melons can be achieved by placing the melon in a bag with ripening apples or tomatoes. The latter will release ethylene gas which will complete the ripening process.
Select melon varieties that will ripen under your conditions. Short season types ripen between 65 and 75 days. Full season types ripen around 85 days.
Poor fruit set could be due to improper pollination, very hot weather or water stress. Pollination may be hindered by cold rain and cloudy weather.
Tasteless melons could be due to dark, cloudy weather, or disease.
The first blossoms often drop off muskmelon plants but this is not a problem. The first flowers to appear on the vines are male. The female flowers, which open later, have a swelling at the base that forms the fruit (the ovary). After bees pollinate these female flowers, the fruit develops!
There are a few insects that occasionally attack melons. Squash bugs feed on foliage and can harm young plants. Squash vine borers can kill plants as they tunnel through the vines. Wilting vines will probably be the first symptoms you will notice. Striped cucumber beetles damage plants by eating leaves as well as stems and fruit. They are also a potential vector of bacterial wilt.
Melon seedlings are susceptible to damping off especially when planted into cold wet soils. In some years bacterial wilt can cause wilt and decline of cucumber plants. Powdery mildew, a fungal disease that causes powdery white spots to form on leaves and vines can infect melons. Look for resistant varieties if this disease has been a problem in the past. Several fungal leaf spot and fruit rot diseases can affect melons. Damage can include brown spots, tattered holes in leaves, sunken brown lesions on vines, and rotted fruit. To avoid these diseases do not grow melons in an area where any member of the squash family has been grown for 3-4 years. Reduce moisture on leaves by providing plants with proper space, controlling weeds, and using drip irrigation or soaker hose instead of sprinkler irrigation. Remove severely infected plants from the garden. At the end of the season, till in plant residue or remove plant debris if infection was severe.
Reviewed by Carl Rosen and Vincent Fritz 2009