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Setting up a Watermelon Garden

Growing & Storing Watermelons
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How to grow your own watermelons from seed?

Nothing compares to eating fresh watermelon that you’ve grown yourself. Kids especially get a thrill out of watching the plant vines spread as the watermelons grow. Plus, there is no better way to avoid herbicides and pesticides. But, if you are thinking about planting a few seeds, make sure you have enough space for the plants to grow. 

Growing watermelons requires lots of space, lots of sun, lots of water and lots of rich soils with lots of nutrients.  They are greedy, rambling vines, like all plants in the Citrullus lanatus (Thunb.), family Cucurbitaceae; e.g. zucchini, squash, pumpkin, cucumbers.  Watermelons are not particularly difficult to grow, but because they are so demanding watermelons may not be a good plant for beginner gardeners. Even so, watermelons are very popular, and who knows, you may get lucky and have all the “right stuff” to grow a large juicy melon!


Where and when can you grow watermelons?

In the true tropics, the dry winter season is the best time for growing watermelon.  Watermelons do not cope well with extreme heat, humid soggy conditions or wet summer season. Fungal diseases and bugs will wipe them out in no time.  If you live in a cooler climate, then summer is definitely the time to grow watermelons.

You do need at least three months of reliably hot, sunny weather to grow and ripen a watermelon. During that time your average daily temperature should be at average around 20-25°C or 70-80°F. Warmer conditions are even better. There are different watermelon varieties, so if you are at region that has shorter summers, look for a faster maturing variety.

Grow watermelons in full sun. You will need an abundant supply of water, rich soil and additional nutrients in order to have a thriving watermelon plant.  And you need space. Watermelons have rambling vine. They like to go wandering and smother everything around them.


Growing watermelons from seed

Watermelons are grown from seed. You may be tempted to use seed out of a melon you bought, but don't waste your time. These days it is almost guaranteed to be a hybrid.  Hybrid varieties are very special crosses that do not grow true to type. You would end up growing what they call pig melons. A melon variety that's only good for feeding to the pigs.

Buy your seed, and if possible buy an open pollinated heirloom variety. Because then you CAN use your own seed next year. The open pollinated varieties are also hardier.  You will find a lot more interesting varieties amongst the heirlooms then you can find in the standard collection of you local gardening centre.

Start your watermelon seeds in the ground, right where they are supposed to grow. The soil should be at least 18°C or 64.4°F for them to properly germinate.

Unless you have an extremely short growing season, do NOT start your watermelon seed in a pot or punnet. Do NOT buy watermelon seedlings from a nursery.  Watermelon seed germinates easily and quickly, within a few days. Watermelon plants will outgrow the seedling stage very quickly, and they do not like transplanting. You do not save much time and you end up with a weaker plant.  Save yourself this totally needless extra work and stick your seeds in the ground, about two centimeters or an inch deep.


Site selection and planting

Watermelon should not follow watermelon, other cucurbits (such as cucumber, squash, or pumpkin), tomatoes, or peppers for at least 3 years.  Watermelons grow best in sandy or sandy loam soils.  Watermelons grown on heavier soils tend to be irregular in shape and may contain less sugar.

Most soils will grow watermelons provided they are well drained.  Before planting, incorporate up to 4 inches of well-composted organic matter for your soil preparation.  Apply 4-6 cups of all-purpose fertilizer (16-16-8 or 10-10-10) per 100 square feet before planting.


Mound, ridge, black plastic mulch or small garden planting methods

If you have a long growing season, you may want to do several plantings, a few weeks apart.

Watermelons need deep, rich, friable soils. To grow watermelons it helps to raise the soil by making mounds, ridges or black plastic mulch. Raising the soil has several advantages.  A mound or ridge is free draining. Melons do not like wet feet. If you have heavy clay soil, definitely raise the bed.

Mound method 

  • Mounds are also good if you have poor soil. By making a mound of good soil with lots of compost in it, you will be able to provide the necessary nutrients to grow your watermelons. A mound that is at least one feet higher than the surrounding ground is a good start.
  •  Many prefer growing watermelons in clumps on a mound, in several different locations in the garden. By mixing things up this helps keep the pests and diseases at bay.  If you want several hills together, keep them about 2 meters or 6 feet apart.
  •  The mound should be about one meter square or 9 square feet (3 feet x 3 feet) and a 1-2 foot high. You can plant about ten seeds in each mound, in three groups of three to four seeds each. The groups are then spaced about a foot apart (30 cm).
  •  In about a few weeks you can see which watermelon plants grow the strongest, and snip off the weaker ones, leaving only one seedling in each group. Do not pull them up, just cut them off, otherwise you will disturb the roots of the other plants.

Row method 

  • If you like growing things in neat rows, or if you want to plant a large area, grow watermelons on ridges, like the commercial growers do.
  • Rows should be about 2 meters or 6 feet apart and the plants spaced at 30 cm or a foot apart.  Sow twice as many as you want, and keep the stronger ones.
  • Row Covers: Hotcaps, plastic tunnels and fabric covers protect seedlings and transplants from cool air temperatures. Row covers enhance growth and earliness. Covers need to be removed when plants start to flower or when temperatures exceed 90F.

Black plastic mulch method 

  • Black plastic mulch in raised beds with drip irrigation has been used successfully with watermelons. 
  • Advantages of plastic mulch include:  soils warm up faster, soil moisture is retained, nutrient leaching is prevented, and weeds are controlled. 
  • Planting in raised beds encourages earlier maturity and improves soil drainage. 
  • A hand corn planter can be used for planting seed through the plastic while a bulb setter or waterwheel setter may be used effectively for transplanting. 
  • Trickle irrigation increases fruit quality and quantity. 
  • In addition, fertilizer can be injected through the irrigation system.
  • Lay the plastic, secure the edges with soil, and cut holes for the seeds or transplants. When using plastic mulches and row covers, seeds or plants can be set out 2-3 weeks before the last frost.
  • Do not apply organic mulches until soils are warmer than 75ºF. Grass clippings, straw, newspapers, and etc., also conserve water and control weeds.

Small garden method 

  • If you have a very small garden but absolutely have to have watermelons, you can try growing them on a trellis. Really! 
  • You need a very strong trellis, you need to train the vines up the trellis as they are not natural climbers, and you need to support the developing fruit so the trellis holds the weight, not the plant. 
  • Putting a loose net around each fruit and tying the fruit to the trellis is an excellent solution.  It is a lot of work but it can be done.


Growing watermelon plants

Watermelons have very shallow roots and they need lots of moisture. The soil should never dry out, and mulch helps with that.  Mulch also keeps weeds down. Weeding could disturb the shallow roots, so it is better to not let them grow to start with.  Black plastic mulch usually works well to remove weed pressure from within rows.

Watermelons are VERY hungry plants. If your mulch is something like compost or aged animal manures that’s even better.  Like all cucurbits, watermelons can handle fairly raw compost and manures.  Otherwise, feed your watermelons regularly with something like pellet chook manure or another organic fertilizer.  Ideally you should use a high nitrogen fertilizer in the early stages, but cut back on nitrogen and switch to lots of potassium once they start to flower and bear fruit.

When the vines are about two meters or six feet long, pinch out the tips. It encourages branching.  As your watermelon vines grow bigger they will start trying to take over more space. If they start to smother other things you can remind them about sticking to their area by gently moving the tips of the vines, so they grow into the right direction.


Watering your watermelon

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. Irrigate so that moisture goes deeply into the soil. To improve flavor, reduce watering amounts as the fruits ripen.


Watermelon flowering and fruiting

Watermelons grows both male and female flowers on the same vine.  The smaller male flowers appear first while the female flowers are much larger that you cannot miss.  If you do not see any flowers, there could be several reasons: either it is too hot, too cold, not enough water, or not enough nutrients. Basically, your watermelon plant is not happy and the condition is not right. 

If the plant does produce female flowers but the little fruit at the base of it shrivels up and dies, then the flowers are not getting pollinated.  Watermelon flowers are insect pollinated. If you suspect the insects aren't doing their job, you can do it yourself, just to be sure.  Hand pollination is best done early in the morning. Pull off a few male flowers and remove the flower petals. Then brush the pollen laden stamen against the stigma in the center of the female flower, so the pollen sticks to it – Easy!

The first few female flowers on each branch will give you the best fruit.  To grow these fruit as large as possible, you can pinch-off the tip of the branch after a couple of fruits have set and are starting to swell up.  This is mixed amongst growers, some feel that this is not an essential step, and you can just let them grow to their potential size.


Harvesting watermelons

Telling when a watermelon is ripe is an art. You will get better at it with practice.

Watermelons are hand-harvested when fully ripe.  Watermelons will not continue to ripen after harvest. 

The presence of a dead tendril at the point where the fruit attaches to the vine helps in determining when to harvest seeded watermelons, but is not useful for seedless varieties. The first sign to look for is the curly tendril at the stem. Once it is dry, as in totally dry and not just starting to dry off, the melon maybe ready. 

The best indicator for ripeness is the change in color of the underside of the melon where it comes into contact with the ground.  However, because this color varies among cultivars, growers must become familiar with the varieties grown to determine the best stage of harvest.  Some starts as a light colored patch on the bottom of the fruit. It is initially greenish, but as the melon ripens the green tinge will start to disappear and becomes a yellowish color. A yellow-white, yellow or a cream-yellow color spot suggests ripeness and a white or pale green spot indicates immaturity. A green watermelon will have a white bottom; a ripe melon will have a cream- or yellow-colored bottom. Those fruit that show a change of color from green or olive-grey to yellowish brown should be considered ready to harvest. Also look for a breakup of green bands at the blossom end of the fruit.  The skin overall becomes duller and tougher.  For best quality, walk the patch daily. 

But the most popular way to tell if they are ripe is the sound. However, “thumping” the fruit is not a reliable indicator of fruit maturity.  You can thump the melon with your knuckles and listen for a dull, hollow sound. The unripe melons have a higher pitched, tighter, metallic ringing or hollow sound. This technique is not perfect however, because the dull sound you hear does not indicate if the melon is overripe.  Keep thumping lots of them and comparing until you can tell the difference.  Eventually you will have to take a chance and split one open.  The only way to get good at this is to grow and harvest lots of watermelons!

Some other possible signs include;

  1. Use the criteria of approximate size for variety.  It's not necessarily true that when a watermelon is big enough, it's ready; but under good conditions, it should be normal size. If it's not, you're probably too anxious.
  2. Ceasing of growth. 
  3. Look at the color on the top. The watermelon is ripe when there is little contrast between the stripes. Another indication is when the surface color of the fruit turns dull. 
  4. The rind at the soil spot should toughen and resist denting with a fingernail when the melon is ripe. Scratch the surface of the rind with your thumbnail. If the outer layer slips back with little resistance, showing a green-white color under the rind, the watermelon is ripe. Feel for development of ribbed indentations that can be felt with finger tips. It should be firm but not a rock. If soft or soft spots it’s too far gone. Sponginess is bad.
  5. Press on it. If the watermelon sounds like it gives a little, it's ripe. (This method can also ruin the quality of the fruit.)
  6. Count the number of days from anthesis (flowering) or the number of days from planting. This works pretty well if you know the variety of watermelon and how many days it's supposed to take for that variety to ripen under normal temperature and fertilizer regimes.
  7. The slipping of the stem from the melon with slight finger pressure is an excellent indicator of melon ripeness in the field. 
  8. Hold a melon up to your ear, if you can feel it squeeze and hear a slight mush instead of a crack it is ripe. 
  9. Rely on your nose, and look for a melon with the strongest fragrance, for this will most likely be the best tasting.  Breath deeply and follow your nose to the sweet ripe melon. Sniff the aromatic one out. Next, look for a melon that is heavy for its size, because if you have two melons of equal size, the heavier one is almost assuredly the riper and better tasting melon. Smell is something you learn with experience.
  10. Still confused? Guess. All indicators will not always work. Take your best shot and go with it.

When harvesting, make sure that the melon is cut from the vine instead of pulled. Pulling creates a cracking wound that pathogens can enter and quickly destroy the quality of the fruit, not to mention ruining the appearance of the fruit. Leave the stems on the melon for as long as possible, and treat for stem end rot after picking.  Melons should be handled gently to avoid bruising.  Do not harvest your melons until they are fully ripe. Melons will get softer after they are picked from the vine but they will never get sweeter.  Cooling harvested fruit removes field heat and prolongs shelf-life.  Watermelons may be stored for 3 to 4 weeks at the proper temperature and relative humidity.


Problems when growing watermelons 

Gummy stem blight is the most widespread and serious disease of watermelon.  Other diseases that can result in crop losses include anthracnose, Alternaria leaf spot, Cercospora leaf spot, and yellow vine decline.  Some disease resistance is available in certain cultivars. 

Watermelon insect pests include aphids, cucumber beetles, and mites.  Slugs and other seedling chomping critters like mulch and they like watermelons. Wait until the watermelons have outgrown the most vulnerable stage, where a slug can demolish them within minutes before you start mulching the area well.


Watermelon Pest Control


The biggest watermelon pest is the leaf eating beetles.  Not only do they damage the leaves, but they also damage the flowers.  For instance, the spotted and striped cucumber beetles, pumpkin beetles with or without dots, whatever you want to call them.  Those orange little buggers all look similar and all do the same: chomp away on your watermelon plants.  However, if they become a real problem it is mainly a sign that your watermelons are stressed.  A healthy watermelon in a balanced environment and in good soil should not attract too many beetles. Also, a watermelon should grow fast enough to cope with a few beetles. 

The other main problem with growing watermelons is mildew, a fungus that makes the leaves look as if they were coated with white powder. The fungus thrives in damp, humid conditions.  The best you can do is to avoid getting the leaves wet. If you cannot avoid overhead watering, do it first thing in the morning so they dry quickly. Never wet the leaves in the afternoon or evening. 

In the tropics, you probably will not be able to control the beetles or the mildew, once the wet season starts. And it is not worth it. The oppressive heat and the humidity is not a good conditions for growing watermelons.


Frequently Asked Questions

My watermelons are not very sweet or flavorful. Is the low sugar content caused by the watermelons crossing with other vine crops in the garden?

  • No. Although watermelon varieties cross with one another, but the effect of this crosspollination is not evident unless the seeds are saved and planted the following year. The poor flavor of your melons may result from wilting vines, high temperatures, or a short growing season in extreme northern areas.

What can I do to prevent my watermelons from developing poorly and rotting on the ends?

  • This condition is similar to blossom end rot of tomatoes and is caused by extremely dry weather when the melons were growing. It may be aggravated by continued deep hoeing, close cultivation or poor irrigation. Mulching the plants with black plastic film helps reduce this problem.


Storing your watermelon

So now that you’ve picked the perfect fruit, how do you keep it fresh? After buying your watermelon, it’s always best to eat it within the first few days. But, if you have to store it, keep it in your refrigerator. You can keep a whole watermelon in the refrigerator for about one week. If your watermelon has been cut into pieces, it should be eaten as soon as possible. Once the fruit has been exposed to the air, it deteriorates rapidly and can take on a slimy texture. Although some people prefer to eat watermelon slightly chilled or at room temperature, its flavor is most vibrant when icy cold.

How to Shop for the Best Watermelon

Picking the right watermelon at the market can often be challenging.

When you are anticipating a juicy slice of melon, the last thing you want is to come home with a watermelon that ends up being soft and mushy.

Watermelons don’t ripen after being picked, so it is crucial that they are harvested at the proper time.

Read more ...