Success with Growing Watermelons

Crimson Sweet Watermelon. Credit Southern Exposure Seed Exchange

 Watermelons are delicious as a snack on a hot day in the garden, helping improve your heat tolerance.  If lightly salted to balance the electrolytes, they can cure dehydration. The seeds, if well chewed to break up the indigestible seed coat, can provide amino acids, fatty acids, vitamin E, potassium and phosphorus. Watermelons are easily digested and add fiber to the diet. Second only to tomatoes as a source of lycopene (said to prevent some cancers), watermelons are also an excellent source of vitamin C, beta carotene, folic acid, biotin, potassium, magnesium and citrulline (an amino acid important for healing wounds and removing toxins from the body).

Watermelon Varieties

Amish Moon and Stars watermelon. Credit SESE

Watermelons are all Citrullus lanatus. After trying several varieties, we chose Crimson Sweet (85d from transplant, OP), a 20–25lb (9–11 kg), striped, 10″ x 12″ (25 x 30 cm) oval melon. It has tolerance to some strains of Anthracnose and Fusarium, and according to Southern Exposure Seed Exchange, it promotes beneficial soil fungi that inhibit Fusarium. We saved seed for many years, selecting for size, earliness, disease resistance and flavor. See Fruit of the Month for September for more about choosing varieties. At this point, you have probably made your choice for this year, and may have them in the ground.

Watermelon Crop Requirements and Yield

Watermelons do best in free-draining light soils that warm quickly in spring. Ensure high organic matter content, sufficient boron and a pH of 6.5. Black plastic mulch, either the removable or the biodegradable kind, will speed growth and ripening. If you want to use organic mulches, put them around the plants after the soil has warmed up, or you will delay the harvest. Drip irrigation is better than overhead, as it reduces the chance of foliar diseases. Water well during fruit development, then cut back during the harvest period for best flavor and to prevent fruit bursting. We often run our irrigation at the same time as harvesting, so we can easily check for leaks.

If drainage is an issue, make ridges or raised beds before planting. You can use straw or spoiled hay in the aisles to absorb some of the water. Watermelons easily die in waterlogged soil.

There are on average 24 seeds/g, 670/oz, 11,000/lb, 24,200/kg. Crimson Sweet seeds are about half the size of others, so need only half as much seed.

Yield of Crimson Sweet and other varieties can be 460lbs/1,000 ft2 (227 kg/m2). For our 6,600 ft2 patch, (613 m2) we can expect an average of 3,000lbs (1,400 kg), whether 150 melons at 20lbs (9 kg) or 300 at 10lbs (4.5 kg). We have got as many as 300 melons from this area, using 2′ x 5.5′ (0.6 x 1.7 m) spacing. More on spacing follows.

Dried watermelon seeds in a paper bag.
Photo Pam Dawling

Sowing Watermelon Seeds

Watermelon seeds need a soil temperature of at least 68°F (20°C) to germinate, taking 12 days at that temperature, but coming up in a mere 3 days at 95°F (35°C). If direct seeding, station-sow 4–6 seeds 1″–1.5″ (2.5–4 cm) deep at the final spacing. Later, thin the emerging seedlings to one or two at each spot. Pests are more likely to attack plants stressed by planting in cold conditions. If in doubt, wait.

Transplanting is the way to go for early melons. It allows young plants to be raised in close to ideal conditions, and it gives the soil time to warm up. We use Winstrip 50-cell ventilated plug flats for this crop, or soil blocks. Cells should be at least 1.5″ x 1.5″ (4 x 4 cm). We put two seeds in each cell and after emergence we pinch off the weaker seedling. We sow 30% more cells than we hope to take to the field, which is another 30% more than we need to plant because of their fragility. Casualties with melons are usually fatal. (We expect casualties on planting day.) We sow April 26.

They come up very fast in our hot germination chamber. Once the seedlings emerge, they need maximum light and warmth, but not too much watering. We transplant at 15–19 days old. Four weeks old is about the maximum for watermelons — they start to get stunted if held too long.

Watermelon transplants in a Winstrip tray on May 2nd. Photo Pam Dawling

Transplanting Watermelons

Don’t rush watermelon transplants into cold soils, it’s better to wait — cold conditions can permanently stunt them. Once outdoor daily mean temperatures have reached at least 60°F (15.5°C) and the first true leaf has fully opened, you can plant them out.

We have found watermelons to be amongst the crops needing the most skill at transplanting. The stems are fragile, the roots respond poorly to disturbance, and spending extra time later replacing the dead plants is frustrating and doesn’t lead to early melons. It also requires the grower to produce lots of spare plants, which all take time and care.

Pulling a roll of biodegradable mulch.
Credit Wren Vile

We roll out drip tape, test it for leaks and then unroll biodegradable plastic over the drip tape and shovel soil along all the edges of the mulch. See our method of using biodegradable plastic, setting it out by hand. The next day we turn on the irrigation while planting. This helps ensure no one stabs the drip tape, and the plants can be set by the emitters. (Yes, you can still find them, even though they are under the plastic.) Watermelon transplants can easily get leggy in the greenhouse, so make holes deep enough to bury the whole stem as well as the roots. We use pointed trowels to punch through the plastic.

We drape netting or rowcover over hoops. This prevents the cover abrading the leaves, creates a volume of warm air around the plants and keeps insect pests away. A week after transplanting, we fill any gaps with more transplants or with a few seeds station-sown at each spot where we want a plant. Sowing pre-sprouted seeds will help make up for lost time if something has gone wrong.

Watermelon Spacing

Spacing can make a difference to size and yield, but not sweetness. There are widely varying recommendations, from 9 ft2 (0.8 m2) to 80 ft2 (7.4 m2) each! The area is the important factor, so choose a row spacing that works nicely for you and adapt your in-row spacing to give the area you want for each plant.

 


Watermelons growing on (torn) plastic mulch. A tented row with rowcover is in the background. Photo Nina Gentle

We used to transplant our watermelons 2′ (60 cm) apart in rows 10′ (3 m) apart. I read about watermelons only needing 10 ft2 (0.9 m2) per plant, so we switched to a spacing of 2′ x 5.5′ (0.6 x 1.7 m), 11 ft2 (1 m2), in order to fit more plants in the space and therefore get more first and second melons. The new spacing seemed fine and the total yield was in the right range. We have tried 2.5′ (80 cm) in-row spacing, some at 3′ (90 cm) and some at 3.5′ (1.1 m). These spacings correspond to areas of almost 14 ft2 (1.3 m2), 16.5 ft2 (1.5 m2) and 19 ft2 (1.8 m2) each. We didn’t keep records and didn’t notice a difference in size. A Brazilian study on Crimson Sweet found that 13 ft2 (1.2 m2) per plant gave the highest total yield, but 15–20 ft2 (1.4–1.9 m2) gave bigger melons.

Factors in Deciding Watermelon Spacing

Total yield (by weight): reduced spacing (to a certain point) increases total yield. Reducing plant spacing 50% may increase the total yield by 37%–48%, while reducing the size of each melon only 10%-13%. Reduced spacing does not decrease the percentage of marketable fruit.

Yield/plant (by weight): decreases at close spacing, sometimes because the number of melons per plant is reduced, sometimes because the size of the fruit decreases. It is not a linear decrease.

Size: reduced plant spacing sometimes affects melon size, but not in a linear way. Other (environmental) factors affect melon size. Bigger varieties are more likely to have their size affected by closer spacing than small varieties are. Small size is an advantage in some markets.

Number of melons/plant: decreases as plant spacing is reduced, but not linearly. At close spacings, the difference is negligible.

Number of melons/area (fruit density): increases with plant density. More plants = more melons.

Early yield: variety, early transplanting, good conditions and hot weather will provide more early melons. The first melon on each plant is the early harvest. More plants means more first melons. Plastic mulch produces crops a month before organic mulch. Spacing has no influence on the ripening rate.

Sweetness: the flavor of watermelon is not related to the size of the ripe melon or the plant spacing. Healthy foliage and long hot sunny days are the biggest factors in building good flavor. August has shorter days than July, and September’s days are even shorter, so don’t expect late-season melons to be as sweet.

Plant health: overcrowding can increase foliar diseases, reducing photosynthesis and sweetness.

Labor requirement: closer spacing = more transplanting. More melons = more time harvesting.

Watermelon with healthy foliage and a flower. Photo Nina Gentle

Clarify your goals and choose your variety and spacing accordingly. If your goal is the highest weight of watermelons for a given area, plant Sugar Baby at 10–11 ft2 (0.9–1 m2) each. If your goal is the highest number of melons, try them even closer! But if you like Crimson Sweet and want fairly large melons, try 15 ft2 (1.4 m2) if 12lb (5.4 kg) melons are an acceptable size (you might still get 15lb/6.8 kg melons!). Otherwise, use 20 ft2 (1.9 m2). Go up to 30 ft2 (2.8 m2) if you want big melons and can accept a lower total yield.

Ideally, the ground will be filled with foliage by the time the first blossoms appear so that the crops can intercept and use all the available sunlight. Given that the market is for early melons, and early ones are sweeter, having many plants (one early melon each), and having them optimally cared for, is important.

Caring for the Watermelon Crop

Remove rowcover from transplants after three weeks (wait longer with direct sown crops) and remove netting once you see female flowers. Pollination is now the critical step, not warming. Pull any big weeds. (Cultivate between the rows if you have bare ground.) Water regularly — drip irrigation set out at planting is the best way to go, as there will be less chance of fungal diseases than with overhead watering.

Watermelons have separate male and female flowers on the same plant, and insect pollinators are necessary. Many species of native bees pollinate watermelons, but augmenting them with honeybees will help pollination, which means bigger, better-shaped melons as well as more of them.

Weeding is important and needs to be completed before the vines run. If big weeds get away from you and pulling them endangers the crop roots, wade in with pruners and clip off the weeds at ground level. This prevents the weeds seeding, and lets the melons get more sunlight again. Do not turn over the vines when weeding — cucurbits don’t like that! Removing damaged fruit will help the good ones grow better.

See Fruit of the Month for September for information on pests and diseases, harvesting and choosing varieties for next year. this material comes from my book, Sustainable Market Farming, where even more info can be found!

Ripe watermelons are a treasure! Photo Nina Gentle

Workhorse Crops for May

Young bush bean plants.
Photo Pam Dawling

Workhorse Crops for May

Workhorses crops are reliable under a wide range of conditions, including weather, soil, date and other variables. Some are easy to grow, some pump out lots of food, some are “insurance crops” like chard that stand in your garden until you need to harvest them, some are especially profitable (for those growing for market).

I’ve chosen 14 crops (including two pairs) to focus on in the next 12 months, ending April 2022: Asparagus, beans, cabbage, carrots, chard, garlic, kale and collards, potatoes, sweet corn, sweet potatoes, tomatoes, watermelons, winter squash, zucchini and summer squash.

My motivation for this series is to help all who want to be more efficient, productive and profitable (if selling) as other parts of our lives expand again.

Workhorse Crops to Plant in May

May is a busy planting month here in central Virginia and probably most places in the northern hemisphere. Ten of our 14 Workhorse Crops can be planted once frosts are behind us.

Beans: We grow bush beans because we don’t like putting up trellises. In the past we had uncontrolled Mexican Bean Beetles that destroyed slower-to-mature pole beans. We found we could get crops of bush beans faster and sow them every few weeks or so to get a good supply of presentable beans every couple of days. Click this link to read about soaking bean seed, using inoculant, sowing through biodegradable plastic mulch using a jig, sowing sunflowers in our bean rows as place-markers when harvesting. See my phenology post for information on when it’s warm enough to start sowing beans (and other crops) where you are.

Carrots: I wrote a lot about carrots in the past year, when the monthly series was on root crops. See this post on preparing beds for sowing carrots, and weeding and thinning. Check out this post on flame-weeding, if you plan lots of carrot-growing!

Multicolored chard. Wren Vile

Chard: A great insurance crop – it provides leafy greens when you need them, and you can ignore it when you have plenty of other vegetables! As a biennial, chard will not bolt the first year (unless stressed by lack of water). We use chard for fresh greens in summer, when kale, collards, broccoli and cabbage from the spring have long gone. Because we don’t need chard until late May, we don’t sow until late March. We transplant in late April, into a hay mulch. This crop will be in the ground until mid-winter, and mulch will keep back most of the weeds. You could, of course, sow chard earlier if you want to eat it earlier. We also grow chard through the winter in our hoophouse, where it feeds us during the Hungry Gap.

Potatoes: I wrote a special series on potatoes last year. Click the link to access the whole series, starting with planting in April. Here we plant in March and June. You can plant at any date in between, so long as you have 80 days until your first frost. If time is a bit short, choose a fast-maturing variety (or be satisfied with small potatoes that won’t store).

Sweet corn: we make 6 sowings of sweet corn, to harvest from July 4 to mid-October. Start planting sweet corn when the leaves of the white oak are as big as squirrel’s ears. Click the link to check our planting dates, and to read about our first sowing of the year, catching raccoons and skunks, avoiding mixing types of corn and to view my slide show on succession planting. There’s a confusing aspect of hybrid corn varieties: if you plant a mixture of different genotypes, it can lead to starchy unpleasant-flavored corn. Also don’t plant Indian corn, popcorn or any kind of flint or dent corn within 600′ (180 m) of your sweet corn. For this reason we grow only sweet corn in our garden.

Our first sweet corn of the season.
Photo Pam Dawling

Sweet potatoes: I wrote about planting sweet potatoes in 2020. Modern varieties of sweet potatoes grow to a good size in as little as 90 days, so they are not just for the South! The further north you are, the longer the daylight at midsummer and the more photosynthesizing the plants can do. I have known people grow sweet potatoes in hoophouses if their climate isn’t warm enough outdoors. This can fit with winter use of the hoophouse for greens and roots. My book Sustainable Market Farming contains a whole chapter on this crop, including growing your own slips, but it’s too late to start that this year. Wait for the soil to warm before planting out your sweet potato slips. We plant ours a couple of weeks after the last frost, around the time we transplant peppers and okra.

Tomatoes: We plant out our main crop at the very beginning of May, unless the weather is too cold. To my surprise, I find I haven’t written much about transplanting tomatoes outdoors. Here’s a post about planting tomatoes in our hoophouse. We use the same techniques in the hoophouse and outdoors. We transplant one row of tomatoes down the centerline of a 4ft (1.2 m) bed, 2ft (60 cm) apart. Outdoors, once the weather has settled so that we’re confident we won’t need rowcover any more, we stake and stringweave. We install a steel T-post every two plants (4ft /1.2 m) apart and start stringweaving when the plants are about 12ins (30 cm) tall. I’ll say more about stringweaving later in the year.

Watermelon transplants in a Winstrip plug flat. Watermelons give earlier harvests from transplants, and plants in plug flats transplant easier then from open flats.
Photo Pam Dawling

Watermelons: Watermelon growing isn’t easy, but the rewards are so wonderful, that I gave watermelon a “Circus Pony” place among the workhorses! We transplant our watermelons, to get ripe ones as early as possible. Melons are tricky to transplant, as the roots don’t do well if disturbed. We have successfully used soil blocks, and these days we use Winstrip 50-cell trays. Watermelons grow very well on black plastic mulch, which warms the soil as well as keeping weeds at bay. The first year we switched from using hay mulch to biodegradable plastic mulch, we were astounded to get ripe melons a full month earlier!

It’s important to keep the little seedlings in the greenhouse warm and in very good light, and away from drafts. Be careful not to overwater. They can keel over very quickly and once the stem collapses, remove that seedling before others die too. The goal is short stems!

When you transplant, get the start out of the flat and into the ground as quickly as possible with as little root damage as you can manage. This is not a crop where one person plops the plants out down the bed and someone follows planting them! Make the hole in the soil (through the plastic if you’re using that), by wiggling the trowel from side to side. Don’t dig a hole as if you are in a sand box, with a spoil heap at the side. Just form a space the right depth to get the whole of the stem in the ground.

Next gently pop the transplant out of the flat, perhaps using a table knife down the side of the cell. Push up from underneath. If all goes well, you’ll have the plant in a little block of soil (yes, like a soil block). Slide the transplant into the hole. You want all the leaves above ground, all the roots and stem in the ground. If the hole is too deep, lift the transplant carefully and scrape some soil into the hole. You don’t want to end up with the plant in a dip, as this can rot the stem. If the hole is not deep enough, you can to some extent hill up soil around the stem to protect it. You don’t want any of that fragile stem visible!

Water the day before, and one hour before transplanting, to help the soil hold together, and so that the plant has some reserves of water to see it through the initial shock of being set out. As you are transplanting, pause and water newly set plants every 20 minutes or so. Afterwards, water the whole planting and repeat on the 2nd, 3rd, 5th, 7th days and once a week after that.

Winter squash: By contrast, winter squash are very easy, and they store for months at room temperature. A true workhorse. We direct sow at the end of May, with the goal of harvesting in September and October, the last ones making Halloween lanterns. Soil should be at least 60°F (15.5°C), and all danger of frost should be past.

Young squash plant.
Pam Dawling

We have grown about 400ft (120 m) for 100 people, and mostly focus on Butternuts, Moschata types that grow best where we are and store longest. This is the type to focus on if you want trouble-free squash, with no damage from borers or cucumber beetles. The tougher stems are better able to repel invaders. They need warm growing temperatures above 60°F (16°C). As well as Waltham Butternuts, we include the large Cheese pumpkin, the long-storing Seminole, and the gigantic Tahitian Butternut. We also grow a couple of Maxima squashes which store quite well:  Cha-cha kabocha, and the large blue Jarrahdale, which have relatively high resistance to squash bugs compared to others in this group. Red Kuri, Festival (sweet dumpling type) and the New England Pie pumpkin are Pepo squashes, suitable for storing a few weeks only. (Pumpkins are squashes.) We grow some of these because they are sooner to harvest. Really they are more of a fall squash than a winter squash.

Winter squash do need a lot of space for each plant. This can mean a lot of hoeing until the vines spread, or mulch. Some can take 90-120 days to reach maturity, so plan carefully to be sure of getting a harvest. For dryland farming, without irrigation, it is important not to move the vines to new positions: the dew and rain drips from the leaf edges encourage root growth directly below the vines (where they get the most water and shade).

Sow 0.5”-1” (1-2 cm) deep. Either “station sow” 2 or 3 seeds at the desired final spacing, or make a drill and sow seeds 6” (15 cm) apart. There are various stick planters and jab planters that can be used for this kind of station sowing. Thin later. Rows will need to be 6’ (1.8 m) apart, or more. 9’ (2.7 m) between rows for the vining ones. Some growers plant in a square pattern so that spaces between rows can be mechanically cultivated in both directions. Bush varieties take less space than the vining types, and rows can be 4’ (1.2 m) apart.

You can transplant winter squash if you need to. We did this one year after our fields flooded. We started seeds in cell packs a week before our usual sowing date of 5/25. It worked just fine.

Summer squash plants under insect netting.
Pam Dawling

Zucchini (courgettes) and summer squash: Zucchini is a subset of summer squash. These are easy to grow, fast to produce warm weather crops. We make a succession of five or six plantings each year, so that we can harvest every day. Each sowing is half a yellow squash (Zephyr, Gentry) and half a zucchini (TenderGrey, Noche, Golden Glory). We grow our earliest squash in the hoophouse, setting out transplants at the beginning of April. Our first outdoor crop is also from transplants. After that, the soil is warm enough to direct sow – 60°F (15.5°C).

After transplanting or sowing, we hoop and cover the row with insect netting (rowcover also works if it has no big holes). We have many bugs that like these plants, especially the striped cucumber beetles, so we keep the rows covered until female flowers appear. At that point we need the service of the pollinators, unless the squash is parthenocarpic (sets fruit without pollination). At that point we pack away the covers, hoe and thin the squash to 24” (60 cm). it would be better to thin sooner, but we rarely find the time.

Zucchini and summer squash are another crop type that we succession sow, to get a continuous supply. More about succession planting another time. The time from sowing to harvest is only around 50 days.

Workhorse Crops to Harvest in May

Asparagus photo by Kathryn Simmons

Asparagus can be harvested if you have a patch. If not start to prepare a patch to plant out one-year crowns next early spring. Remove all perennial weeds while growing a series of cover crops. If you have asparagus, you probably know to snap off at ground level all the spears above a certain length. We chose 7” (18 cm). Do this every day for the 8-week harvest period. Daily harvest will also remove asparagus beetle eggs, controlling the pest level.

A bed of Early Jersey Wakefield cabbage in mid-May.
Photo Pam Dawling

Cabbage can be ready from late May, if you made an early sowing of fast-maturing varieties. Farao or Early Jersey Wakefield can take only 60 days.

Carrots can be ready from late May, if you sowed some in mid-late February

Chard is ready for harvest from late May (earlier if sown earlier), see above.

Harvesting garlic scapes in May
Photo by Wren Vile

Garlic scapes appear in hardneck garlic plants. Here it is also an indicator that our garlic will be ready to harvest in three weeks.

Kale and collards can be harvested until they are bolting, as long as the flavor is acceptable. Read more about bolting here.

Zucchini and summer squash from mid-May,

From storage: carrots, potatoes, sweet potatoes, winter squash

Workhorse Crops Special Topic: Deciding Which Vegetable Crops to Grow

Here’s a slideshow to help you decide which crops to grow. Some of the points are for commercial growers, some apply to anyone growing vegetable crops.

Deciding Which Vegetable Crops to Grow, Pam Dawling