15 Growing Watermelon Questions Answered…

Originally appeared at National Gardening Bureau.

Growing watermelon can be done successfully in all parts of the country. For those gardeners in northern or cooler climates, where hot days may not be long enough, choose an earlier-to-mature variety like AAS Winners ‘Shiny Boy’, ‘Golden Crown’, or ‘Yellow Baby’ that all mature in 70-75 days.

For a smaller variety that will fit in the refrigerator easily, try one of these newer ice-box AAS Winners like ‘Mini Love’, ‘Cal Sweet Bush’, ‘Gold in Gold’, or ‘Mambo’. Or go for the glory and sow watermelon seeds for an extra-large whopper like the 30-35 pound 1950 AAS Winner ‘Congo’. Heirloom fans will want to plant ‘Moon and Stars’, introduced in 1926, with a deep green skin speckled with tiny yellow stars and quarter-size moons.

National Gardening Bureau watermelon breeder members answer 15 FAQ on growing watermelons in your Victory Garden 2.0. These answers will help you grow refreshing watermelon this season.

1. What soil temperature is best for growing watermelons?
It is recommended that soil temperatures be 70 degrees Fahrenheit or above for seeding or transplanting watermelons. Melons were originally from Africa and Southern Asia, they thrive in warm long season conditions. If you live in a cooler climate, consider applying a plastic mulch before seeding or transplanting your melons. This will help warm the soil during cool nights, control weeds and help with uniform irrigation.

2. What are the major pests to watch for and how do you organically prevent them?
Surprisingly there are actually very few insect pests for melons and watermelons. The plants have many pubescence (hairs) that act as natural protection against pests. Crawling insects like flea and cucumber beetles can be controlled by floating row covers, diatomaceous earth, and organic insecticide soap applications. Be careful using oil-based biocides, in high light and hot conditions these products can burn the plants after applying. Also, consider releasing predator insects like Lady Bird Beetles to help control aphids and thrips. If you choose to release beneficial insects make sure to do this weekly for a month to create long term control.

3. Does watermelon need more water than typical fruiting plants (such as tomatoes) because the fruit is so large and mainly water?
These desert-inspired plants are actually very adapted at storing water. The fruits are indeed mainly water and a wonderous storage vessel for needed moisture in the dry climates. Since watermelons have survived in arid climates for centuries, they are well adapted at growing in minimal water conditions. Match your irrigation schedule to the plant’s needs. Too much water is much more detrimental to watermelons than too little. Over irrigation creates root pathogens that are difficult to control. At later stages, too much water can split fruit, apply minimal irrigation after fruits begin to ripen. Water in short intervals and do not let irrigation come into contract with the crown of the plant. Remember there is a complex set of roots below ground just like the vines above ground that feed the plant with moisture and nutrients.

4. Does the watering schedule change based on fruiting or not?
Watermelons are arid plants that do not require as much water as you think. Like most plants when larger, setting or sizing fruit, they require more irrigation than at earlier stages of growth. Your watering schedule should be based on the actual growing conditions and weather. In longer warmer days, plants transpire more than in cooler shorter days, just like we do. Consider frequent short irrigation cycles instead of a long soaking one. It is easier to harm your watermelon with too much irrigation than too little.

5. How long are most melon seeds viable if properly stored?
If properly stored at the optimal recommended rates: below 60 degrees Fahrenheit and 30% humidity, melon seeds can be viable for many years. A common rule of thumb for seed storage is that the temperature (in Fahrenheit) plus the relative humidity in the air (in percent) should total less than 100 for satisfactory seed storage. Remember humidity is the real killer when considering seed storage. Seeds are quite happy to be stored in any dark, dry, and cool location for many years. As the seed is stored and ages, the germination, and vigor are reduced. For best seed performance it is recommended to use seed packaged for the indicated growing season.

6. Any way to sweeten a watermelon or does it naturally grow like that?
Watermelons have naturally high levels of sweetness/sugars. One way to enhance the sweetness of your watermelon is to reduce the irrigation during the ripening stage. Sweetness can also be related to genetics; some varieties are recorded to have higher sugar levels when tested. A fun fact: seeded watermelon typically have higher sugar scores (Brix) than seedless watermelon.

7. Do watermelon plants need nitrogen?
Watermelons are not heavy nitrogen feeders, actually, too much nitrogen can create excessive vine growth and less fruit set. In commercial production fields, most melon growers apply less than 100 units of nitrogen per acre. A well balanced 15-15-15 or 10-10-10 fertilizer works great in a garden setting. The rule of thumb when applying a dry fertilizer to garden beds is to broadcast 3-4 pellets of fertilizer in a quarter size area before working the soil or overhead irrigation.

8. How much space does a growing watermelon plant need? Are there varieties for small spaces?
Watermelon can be grown easily in smaller garden areas with bush varieties. Try seeding a watermelon variety like Cal Sweet Bush, Mini Love, or Sugar Baby Bush in your smaller garden. The vines only reach 18 to 20 inches instead of 3 plus feet. Plant bush watermelon in hills of 2 plants about 12 to 14 inches apart. You should be able to grow one nice watermelon on every bush plant. Also, consider growing your standard vining watermelon vertical, train your large vines up like runner beans. Do not forget to support the fruits with a hammock as they grow. Big and little kids love to watch melons and watermelons grow vertically.

9. What kind of light do watermelon need and do they need heat as well? Can I grow them in zone 8 Willamette Valley in Oregon?
Yes, transplant or sow watermelon only when soil temperatures are above 70 degrees Fahrenheit. In cooler and shorter seasons watermelons can be transplanted but do not like their roots overly disturbed. Remember these warm-season desert annuals do not like night temperatures below 50 degrees and are very cold sensitive. In cooler growing areas consider using a plastic tarp to increase ground temperatures to above 75 degrees Fahrenheit. Soil temperatures at 75 plus degrees and 10 plus hours of sunlight are considered optimal. Also, consider growing a 70 to 80 day maturing or short-season variety like Tiger Baby or Sugar Baby.

10. What do I need to know about the blooms and pollination?
Watermelon vines produce both male and female flowers. Bees are necessary for pollination, as is the timing, meaning both male and female flowers need to be open at the same time. Sometimes, there may not be a pollinator present, in which case, the plant can be hand pollinated.

You might notice the blossoms dropping off the vines prematurely. This could be due to plant stress (such as a lack of pollination, lack of nutrients, or improper irrigation) so be sure to plant in fertile soil and keep the plant evenly watered.

11. I get opinions that are all over the place when talking about when to pick a properly ripened melon.
There are many wives’ tales about picking the perfect summer melon. One of the easiest ways to tell if a watermelon is mature is by looking at the small leaf (pig’s ear) next to the curly tendril at the stem end of a watermelon. If the pig’s ear and tail are dry or almost dry, the watermelon is ready to eat.

12. What about vertical gardens? My zone is 10B and I live in a 30th-floor apartment with a high balcony facing SW., In the summer, you can call my balcony (Devil’s Front Door) so with this info in mind is there a possibility to grow those gorgeous watermelons in a 5-gallon bucket on my balcony?
For a vertical watermelon wall, plant watermelon seeds in a large half wine barrel in front of a sturdy wooden structure or supported metal fence panel. Train the watermelon vines up and entwine in your well-braced structure, remember even small watermelons reach weights up to 10 to 12 pounds. Consider a small icebox variety, 10 to 12-pounds, for easier trellising. As the fruit begins to size add a hammock-like fruit support that can grow with fruit expansion. This well attached cloth or netted fruit support will need to be sturdy enough to hold the entire weight of your watermelon. Some people even add a waterproof stool or chair to support the fruit weight later in the growing cycle.

Water is going to be a real challenge in your situation. If you have enough space for two large containers, I would also try a small, mixed variety gourd to intertwine with your watermelon vines. The gourds vines and leaves will help shade your watermelon fruit from sunburn and add an ornamental fall look when the plants mature.

For a vertical watermelon wall for those who can plant inground, plant watermelon seeds in a hill in front of a sturdy wooden structure or supported metal fence panel. Follow the same trellising and support instructions as above.

13. Which variety grows best in Zone 8 and are seeded? I’m not a fan of the seedless variety.
Believe it or not one of the best overall performing watermelons is an heirloom, open-pollinated variety – Moon and Stars Red. These large 30 pound plus watermelons have dark green rind with small yellow spots (stars) and typically one large golden spot (moon). The flesh is very sweet, red, and has ok firmness for a variety that has been around since 1926. Even the leaves are dotted with yellow spots. If you like yellow flesh watermelon try Moon and Star’s Yellow.

14. How are seedless watermelons created?
Seedless watermelons are a hybrid that creates a genetic dead end. Both the parent lines have seeds, when they are crossed the progeny is seedless or triploid. What happens when you cross a horse and donkey? You get a mule. A mule is sterile and cannot reproduce, just like seedless watermelon. You have to grow a pollinator or seeded watermelon next to a triploid to even set fruits. Seedless watermelons can have undeveloped white seed coats inside the flesh, but even a fully colored dark seed coat has no embryo.

15. I have been growing watermelons, is growing cantaloupe similar?
Watermelons and cantaloupe are very similar to grow; both are heat-loving annuals. The important thing to remember is that these vining plants need plenty of space, warm soil temperatures, and long day length for best results. It is recommended that soil temperatures be 70 degrees Fahrenheit or above for seeding or transplanting melons. Remember melons were originally from Africa and Southern Asia, they thrive in warm long season conditions.

The easiest way to tell if a cantaloupe is ready is when the fruit will “slip”. Slip is defined when the stem attached to the melon separates easily with a strong tug on the stem. This separation typically occurs when the fruit is mature.

Melons like honeydew typically do not slip, so you must guess when the fruit is ripe to eat. Use the following strategy for choosing ripe melons that do not slip: when the shiny surface of the fruit rind is replaced by a dull almost grey/white cast, they are ripe. Most melons have this dull waxy look to them when they reach optimum maturity.

Still, have a question about growing watermelons in your Victory Garden 2.0? Visit National Gardening Bureau and ask their NGB Member Experts.

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