What summer picnic would be complete without watermelon?
Sweet, refreshing, and adaptable, watermelon is another easy-to-grow addition to your foodscape.
Botanically, watermelon is a type of berry called a pepo. It is also a gourd. As a member of the cucurbit family, watermelons are cousin to cucumbers, squash, pumpkins, and other melons.
History of watermelon
Watermelons were cultivated 5,000 years ago, in Ancient Egypt. Watermelon seeds were even found in King Tut’s tomb! Watermelon ancestors were not the bright red, sweet fruits we know. In fact, the original watermelons tasted pretty awful. They were bitter and hard. People grew them anyway, because these melons could hold water for weeks and even months, if stored properly. [That’s how they got their name - get it?] Five thousand years ago, that was a really Big Deal. As plumbing became a thing, watermelons had to up their game. Over time, and with selective breeding, they became the sweet summer picnic favorites that we love.
How to grow watermelon
Watermelon plants (Citrullus lanatus var. lanatus) can take up some space. The 5-sided vines may reach 10 feet in length and the leaves are large. Plant watermelon seeds one inch deep in groups of 6 to 10 seeds. These seeds should be planted in ‘hills’ that are 3 to 4 feet apart. These hills are mounds of loose, rich soil two feet in diameter. Once seedlings emerge, save the best 3 and snip the others off at ground level. Mulch around the plants to reduce weeds and retain moisture. Individual watermelons can be grown in a container, but it should be large - at least 5 gallons. They can also be grown up trellising or on stock panels, but each melon will need a hammock.
In the Bay Area, it is best to plant watermelon in May and June, though seeds can be started two weeks after the last frost date. Seeds will not germinate at temperatures below 70 degrees F. Row covers can be used over seedlings to protect them from pests and to retain some heat. Watermelons prefer a soil pH of 6.0 to 6.8. Watermelons do require a significant amount of water to produce fruit, but avoid getting the leaves wet to prevent fungal disease. If the leaves wilt in the afternoon, don’t worry about it. If they stay wilted into the evening, check moisture levels. Once fruit starts to appear, you will want to get it up off the ground with some straw. This reduces the chance of belly rot. Reduce watering just before your watermelons ripen to increase sugar levels and intensify the flavor.
Watermelon pests and diseases
Like most plants in the Bay Area, watermelon are likely to be attacked by aphids, cutworms, crickets and grasshoppers, armyworms, cabbage loopers, leaf-footed bugs, earwigs, flea beetles, leafhoppers, leafminers, nematodes, slugs and snails, thrips, whiteflies, and spider mites. As a cucurbit, watermelon is also subject to stinkbugs, cucumber beetles, and squash bugs. Many of these pests can be throated by dusting your melons with kaolin clay, a non-toxic fine powder that clogs up their breathing holes. Diseases that can affect watermelon include damping off, powdery mildew, downy mildews, verticillium wilt, root rot, fusarium wilt, angular leafspot, curly top, and white mold. Nearly all of these diseases are related to overhead watering, so don’t do it. Most watermelon varieties are resistant to anthracnose, but seedless watermelons (below) are not. Unlike other cucurbits, watermelon is not susceptible to cucumber mosaic and I have no idea why. Unsuitable environmental conditions can lead to blossom end rot, bitter fruit, blossom drop, and poor pollination.
One nice thing about growing watermelon is that you can plant the seeds in a raised bed, straw bale, or container, and then let the vine cover unplanted areas, or areas that are looking poorly. The large leaves shade the ground, stabilizing temperatures and making the soil more habitable for worms and beneficial soil microorganisms. Add a little mulch and you can be preparing that area for planting next season!
Add a watermelon plant to your foodscape every summer and save the seeds for next year's crop!
Note: What’s up with seedless watermelons?
Seedless watermelon production began in the 1990’s. This is how seedless watermelons happen:
Now you know.
Sweet, juicy melons are a gardening favorite. Easy to grow, productive and delicious, what’s not to love?
It just wouldn’t be summer without slicing through the hard outer rind of a melon and devouring the sweet, refreshing wetness within.
Melons are members of the Cucurbit family, along with pumpkins, squashes, and even luffas! Within the melon family, there are several different groupings (by genus) of some familiar, and some not so familiar, melons:
How melons grow
Like their cousins in the squash family, melons grow on vines. Unlike other vegetables crops, however, each vine has both male and female flowers. The male flowers generally appear first and usually only last for one day. Melon pollen is vert sticky, so wind pollination does not occur. Honey bees are needed to carry the pollen from one flower to the next. If there are not enough honey bees in your area, you can use a fine paintbrush to transfer the sticky pollen to the female flowers, or you can break off a male flower, remove the petals, and apply the pollen that way. [I collect the pollen-carrying stamen for hand-pollinating, just in case.] Female flowers can be identified by the miniature fruit (ovary) at the base of each blossom.
How to grow melons
Melon seeds are big and easy to work with. In the Bay Area, melons can be planted in May and June. They really love hot weather. Prepare the planting area by digging compost into the soil and creating hills. Each hill should be approximately 4 feet square. Plant 3 to 5 seeds, one inch deep and two inches apart, into the middle of each hill. Water the area well. Once your seeds have sprouted and grown into seedlings with a few sets of leaves, snip the smallest plants off at ground level, rather than thinning by pulling them out. This lets the remaining plant’s roots and helpful soil microorganisms stay undisturbed. Melons need to be watered every 2 or 3 days during the peak of summer. Sometimes even more. Regular watering can help prevent the fruit from splitting open. Side dressing melon plants with aged compost during the growing season also improves both crop quantity and quality. Side dressing simply means putting compost next to the plants and watering all those yummy nutrients into the surrounding soil. Easy and effective.
You may want to add a layer of straw or sawdust under your melons, to get them up off the ground. This helps prevent rotten areas, and insect and fungal infestation. Melons can also be grown in containers, towers, or straw bales, and trellised. The fruit itself will need personal hammocks if you use a trellis. You can tell a melon is ready to harvest when you see a slight crack around the stem where it is attached to the fruit. This is called the “full slip” stage. Crenshaw, casaba, and some honeydew varieties do not develop a slip. Casaba and honeydew melons can be stored for several weeks, while other varieties are best eaten right away.
Troubleshooting melon problems
Melons are susceptible to the same problems as cucumber, pumpkin, and squash. Use the symptoms listed below to find (and solve) your melon problems!
Cutworms, wireworms, crickets and grasshoppers, various beetles, earwigs, stinkbugs, and thrips may also try getting into your delicious melons, so be vigilant! (A light dusting of diatomaceous earth might help, too.)
All too often, gardeners hear the myth that members of the Cucurbit family can cross-pollinate. This is simply not true. Pollination between different species does not occur. What can happen is two different types of melon can cross-pollinate. In fact, that’s how Crenshaw melons came about - Persian melons were crossed with casabas.
As you prepare to start growing your own melons, be sure to Plant It Forward with any leftover seeds!
Spring is the time of year when it is common to see a white powder appear on the leaves of cucumber, melon and other cucurbits. You may also see it on tomatoes, roses, snapdragons, chrysanthemums, peas, artichoke, beets, grapes and practically everything else. This bane of gardeners is called powdery mildew.
What starts as a small white spot, powdery mildew expands to engulf an entire leaf as the nutrient-sucking fungi bleed the life from your garden. It can be found on either side of a leaf and sometimes on stems.
Powdery mildew is a fungus. It is caused by different types of fungi (e.g., Erysiphe spp., Sphaerotheca spp.), depending on which plant is affected. Contrary to common belief, moisture and humidity are not needed for these fungal beasties to appear.
Powdery mildew fungi simply need living plant tissue to survive and thrive. To make matters worse, their spores are carried on the wind, so the battle never ends. The reason powdery mildew seems to disappear in the heat of summer is that these microorganisms prefer shade and temperatures between 60° to 80°F. Our California summers are simply too hot for the spores to reproduce. Instead, they remain dormant until conditions improve.
The white powder seen on leaves is actually thin layers of fungal tissue (mycelium). Other symptoms of powdery mildew include:
Not only does powdery mildew cause leaf loss, it can also weaken a plant. This lowers production and increases susceptibility to other pests and diseases, such as Citrus Blast. Leaf drop can also lead to sunburn damage.
Prevention and vigilance are the best ways to counteract powdery mildew. These tips can help, but nothing will eliminate powdery mildew in the garden:
Now, some people recommend spraying plants with a baking soda and water spray. I have had mixed results, but other people swear by it.
You reach in to deadhead a rose and a tiny white insect flies out from under a leaf. On the underside of that leaf is a strange white spiral. You have discovered whiteflies.
Whiteflies are not related to flies at all. Instead, they are close cousins to aphids, mealy bugs, soft scale and armored scale.
Whiteflies got their name because most whitefly species look like tiny white flies. Adult bodies are actually yellow, but it’s hard to see. They have 4 white wings and are often no bigger than 1 mm. Some whitefly species are black or yellow. You can see a chart of the most common whiteflies found in California at the UC IPM Pest Note on whiteflies.
Whiteflies are quick and very difficult to see. It is much easier to tell if a garden is infested with whiteflies by noticing white spirals on the underside of leaves. These spirals are whitefly eggs. The adult walks a spiral path, laying eggs in a waxy trail that holds the eggs to the leaf. In warmer parts of California, whiteflies can breed year-round. Whiteflies go through four instars. Eggs hatch out nymphs (crawlers). The next three stages are nearly immobile, much like scale insects. The final instar is a pupal stage. At each stage, these pests are sucking plant juices, spreading disease, and leaving a behind drops of honeydew. Whitefly larval feeding can distort leaves and cause significant losses in some vegetable crops.
Whiteflies can reproduce at mind-boggling rates. They use piercing mouthparts to suck the sap from the phloem of a wide variety of garden edibles and ornamentals. Heavy infestations can cause leaf drop. The honeydew (sugary poop) left behind is host to sooty mold. Honeydew also attracts ants, which then protect whiteflies from their natural enemies. Some whitefly larva may transmit viral diseases and adults can also carry pathogens. Low whitefly populations are not a significant problem, but they can make citrus, pomegranate and avocado trees look shabby.
How to control whiteflies
Natural predators are the best defense against whitefly. Very often, population explosions are caused when gardeners apply broad-spectrum pesticides that kill off predators, or when ants are allowed free access to host trees. Ants can be prevented from protecting whiteflies by applying sticky barriers around the trunks of trees and shrubs. Dusty conditions can also put the odds in favor of whiteflies. Hosing off dusty plants can help reduce whitefly populations.
Heavy whitefly populations are very difficult to control. Any leaves with whitefly eggs should be removed and discarded. If the leaf looks particularly healthy, you can simply rub your thumb over the eggs to destroy them. Reflective mulches repel adult whiteflies, aphids, and leaf hoppers. Also, yellow sticky traps can be used to trap and monitor whitefly populations.
According to companion planting lore, whiteflies can be discouraged from an area by planting basil, mint, thyme, and nasturtium. Whitefly predators, such as parasitic wasps and flies, and hummingbirds, can be attracted to an area by planting zinnias, bee balm, hummingbird bush, and pineapple sage.
Mites are tiny spiders that suck the living juices from nearly a thousand different garden plants. Being closely related to ticks, some varieties of mites also suck blood from mammals, like us! The study of mites and ticks is called acarology.
Mites prefer soil that is high in organic content with plenty of moisture. Unfortunately, that describes nearly all of our container plants and many of the microclimates found in Bay Area gardens. A highly adaptable critter, there are over 42,000 species of mites worldwide. Aside from nest mites, dust mites, varroa mites, and many others that attack birds, animals, and bees, respectively, common garden mites include gall mites, spider mites, and thread-footed mites.
Spider mites get their name because they build protective webs around eggs and feeding areas. The most common spider mites in the Bay Area are the two-spotted spider mite, the strawberry spider mite and the Pacific spider mite. They are often found on the underside of leaves, where they pierce plant cells to feed. These mites are very small, usually less than 1 mm (0.04”) long, so they are all too easy to overlook until the damage becomes significant. It doesn’t take long for a population to develop, either. A single female can lay 20 eggs a day and live for up to 4 weeks. Since each offspring hatches within 3 days and becomes sexually active in only 5 days, a single, fertilized female and her offspring can produce millions of spider mites in a single season!
An interesting note: female spider mites have two sets of chromosomes, like we do, but males only have one. If an egg is fertilized, it will hatch female. If it is not fertilized, it will hatch as a male. Also, female spider mites are able to “decide” whether to lay male or female eggs, depending upon environmental conditions. To control spider mites, insecticidal soap is your best bet. Neem oil, diluted and combined with a surfactant (dish soap) can help. If chemical pesticides are used, repeated applications will be necessary (and progressively ineffective, as mites can develop resistance).
Most thread-footed mites, also known as white mites, feed on fungi and algae, a few varieties have evolved to attack leaves. Specifically, the cyclamen mite and the broad mite are able to inject toxins that thin the cell walls of mature leaves. Damaged leaves display puckering, twisting and stunting.
The only known effective chemical pesticides against mite infestations are endosulfan, dicol, and ethyl bromide fumigation. Endosulfan was globally banned due to its toxicity to humans and its ability to accumulate in an environment, dicol is considered a “moderately hazardous” pesticide, closely related to DDT, and the state of California classified ethyl bromide as carcinogenic and a reproductive toxin - not anything you want to be spraying on food plants. Broad spectrum pesticides do more harm than good because they also kill beneficial insects that feed on mites. You can buy predatory mites that help control mite infestations. If an infestation is discovered, sprays of water, insecticidal oils (neem, cottonseed or canola) soaps can be used to displace mites and make life harder for them. Garlic extract and oil of clove, rosemary, cinnamon, mint and others can also be effective. These natural treatments can be dangerous to plants, however, so use them carefully. The same goes for sulfur, especially on cucurbits. Observation and prevention are far easier than eradication.
One of the easiest ways to avoid mite infestations is to create a quarantine area for new plants. This protects established plants from new infestations and gives you the time needed to see if a new plant is carrying any pests or diseases. Also, proper irrigation reduces water stress in established plants, making them better able to protect themselves. Mites prefer dusty conditions, so keeping garden paths, trees, shrubs and other areas clean can significantly discourage mites. Encouraging beneficial insects, such as lady beetles, lacewing, and pirate bugs, by providing water and habitat, can significantly reduce mite populations without the use of pesticides or sprays.
Cucurbits refer to the gourd family and it includes squash, pumpkin, zucchini, melons and even luffas! Most of the 975 species are susceptible to frost and many are trailing annual vines.
Watering early in the morning allows the leaves to dry out before evening, helping to prevent powdery mildew and other fungal diseases. Because of the wide leaf coverage of most cucurbits, weeds are seldom a problem. Cucurbits are frequently attacked by squash vine borers and squash bugs, so squash those bugs whenever you see them!
Be sure to harvest fruits regularly, to ensure continuous production. Once plants believe they have completed their reproductive cycle, you generally won't get any more fruit.
Yesterday, I curb-scored 8 very nice tomato cages. While they come in a variety of sizes and shapes, the most common type are concentric circles held at different heights, usually with three legs.
I hope this information inspires you to grow more of your own food. You can ask your garden questions on my Home page.