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Kimber's watermelon

How to Determine When to Harvest Watermelon

Do you have questions about watermelon? When do you harvest watermelon? Why does my watermelon look funny? What’s happening to the leaves?

Kimber's watermelon

It’s watermelon harvesting time. Did you grow watermelon for the first time this year? When do you harvest watermelon? Why are the leaves changing? You probably have a few questions. Luckily, you’re in the right spot for some quick answers.

How long does watermelon take to grow?

The exact time varies based on the type of watermelon you’re growing. On average planting to harvest time is between 70 and 85 days. Small watermelons, such as sugar babies, take less time to fully ripen (70-75 days) than larger ones such as Queen of Hearts (80-85 days). It all depends on when you plant and what your gardening conditions are of course.

When should you plant watermelon?

Watermelon is a warm weather crop. Plant it when the soil is at least 60 degrees (15°C). You can start seeds inside as much as six weeks before your last frost date to get a head start or directly sow the seeds when the soil warms up. Watermelon will not survive a frost so make sure your night temperature isn’t forecasted to dip below 50° (10°C). The colder the weather, the less sweet your watermelon will be, so don’t plant them too early.

How do you care for watermelon?

Watermelon needs a full day of sun and soil rich in organic matter. It also needs plenty of water and fertilizer. The heat will sweeten the watermelon but it will also have the leaves looking wilted by the end of the day. Don’t panic. They’ll perk up again. Just make sure to consistently water the plants. They have shallow roots and can dry out quickly. You can pinch off early blossoms to promote better growth. You can also support the vines with trellis.

watermelon on trellis
When do you harvest watermelon?

This is a little tricky. There are signs that a watermelon is ripe, but truly it is a guessing game. There is one important thing to know: once a watermelon is cut from the vine it will not continue to ripen. So how do you know if a watermelon is ready to be harvested? Here are the signs to look for:

  • The curly tendril on the vine just above the watermelon will turn brown and wilt.
  • The part of the watermelon that is touching the ground will turn yellow. We call this the field mark.
  • As you’ve likely seen someone do in the grocery store, give the watermelon a thump. If it has a dull hollow sound, it’s ripe.
  • Finally, the color of the watermelon will soften to a dull finish.

Every watermelon won’t necessarily have all of these signs. It’s up to you to spot the ones you can and then harvest them with your best judgment.

How do you know if a watermelon will be sweet or watery?

Did you know that there are male and female watermelons? Male watermelons are long and oval shaped. These are generally more watery. Female watermelons are circular and sweeter.

female watermelon
watermelon harvested
What makes a watermelon oddly shaped?

All watermelons aren’t the same. While the watermelon below looks like it cross pollinated with a summer squash (which it can’t actually do), it is oddly shaped because it wasn’t fully pollinated. Bees and other pollinators have a very short window of time to pollinate female flowers on watermelon vines. These flowers open shortly after sunrise and close in the afternoon, never to open again. All three lobes of the stigma must be pollinated or the watermelon will be misshaped.

Why does the watermelon have white swirls inside?

We cut this watermelon open and discovered beautiful white swirls. This watermelon was not fully pollinated either, but it is beautiful and sweet. Don’t be afraid of imperfection.

What are the brown scars on the watermelon?

Don’t toss that watermelon. The brown or beige “scars” on the side of the watermelon are a good sign. That is where the bees tasted the pollen. Watermelons with these marks are usually sweeter than others.

watermelon odd shape
watermelon swirls
watermelon bee kissed
Why are the watermelon leaves changing color?

As watermelon season comes to an end, you’ll likely notice the leaves changing. If all is well and balanced in the garden, they should simply be dying off after completing the growing season. If your leaves are yellow or develop brown spots however, there’s a problem.

Yellow leaves can be a sign of one of these three things: nitrogen deficiency, Fusarium Wilt or Southern Blight. If nitrogen deficiency is the culprit, you might simply need to water more and add mulch. If your soil is lacking in nitrogen, which you can find out with a quick soil test, then add fertilizer. Unfortunately, if the problem is Fusarium Wilt there isn’t anything you can do to save the plants. They will need to be pulled and discarded. Fusarium Wilt is a fungi that slowly blocks water and nutrient absorption. Leaves and vines yellow and die from being unable to receive vital nutrients. Southern Blight is just as devastating and untreatable. It works in a similar way, but evidence of its arrival is more quickly visible. Usually the fruit will rot and die early on and then the leaves will yellow and die. There is nothing that can be done to stop the spread of Southern Blight.

Brown spots on leaves are another sign of trouble. On a positive side, if the brown spots are caused by Alternaria Leaf Blight, then it is treatable with neem oil. Brown spots on leaves that start small and grow into irregular shapes may be Alternaria Leaf Blight. If untreated, leaves may die. A quick treatment of neem oil can save the plant though. Angular Leaf Spot is characterized by angular brown spots. Copper fungicide can slow the spread of this disease, but leaves need to be able to stay dry for any lasting positive results. If the entire leaf, and even the stem, has turned brown then your plant might be suffering from Phytophthora Blight. Unfortunately, this disease is not easily treatable and the best course is to remove the plant.

Hopefully you’re harvesting delicious watermelon and not facing any of these problems.

Did you plant watermelon this year? How did it go? Share your adventure with us in the comments.
watermelon in basket
yellow petaled flower by elias sorey unsplash

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