We may receive a commission on purchases made from links.

A tasteless watermelon is the ultimate summer bummer. Preventing this problem is easier when you’re picking watermelons growing in your backyard rather than purchasing them at a supermarket. That’s because you probably know what types of watermelons you’re growing and when their seedlings started poking through the soil. These two details can tell you which of your garden’s melons are most likely to be ripe — and, by extension, sweet. These hints are even more useful when combined with other tried-and-true tips for telling if a watermelon is ready to harvest.

Most seed packets share several useful nuggets of information, including how far apart to place the seeds, how long the germination process is likely to be, and how many days it takes for a brand-new seedling to produce a mature fruit or vegetable. Keep the packet or write down the “days to maturity” number to remind yourself when you should harvest your watermelons. If you remember when every one of your seeds sprouted, it’s possible to predict which of the fruits in your garden will be ready first. Plus, counting down the days until you can harvest each of your melons makes the gardening experience a bit more exciting. This harvest countdown method hinges on the assumption that totally ripe watermelons will have the flavor you desire. It’s also important to harvest at the right time so you don’t end up with another summer bummer: rotting watermelons.

Keeping track of the dates and numbers you need increases your chances of success with the harvest countdown method. In addition to saving your seed packets, label each watermelon seedling with the date it emerged from the soil. Even if you plant all at once, your seeds are likely to germinate at different times, so it’s important record the order in which they made their debut. You can make DIY garden labels from household items to assist you with this task. If you’re pressed for time, grab a handful of white plastic spoons and a permanent marker to make quick-and-dirty signs for your watermelon vines.

One caveat to keep in mind: Counting the days between germination and maturity is helpful for finding the ripest watermelon in your crop, but it’s not a guarantee that your watermelon will have flawless flavor. Differences in sun exposure, soil nutrients, water intake, and other inputs can affect the taste of melons, even those planted in the same yard. If your soil is lacking in magnesium, for example, adding Epsom salt may lead to sweeter watermelons. Before trying this hack, check your garden’s nutrient levels with a product such as the MySoil test kit. Giving your plants too much magnesium can hamper their growth, which takes a toll on their fruit. The variety of watermelon you’re growing is also a factor when it comes to sweetness. Some types — Allsweet and Bradford Family, for instance — have a reputation for being sweeter than others.