You probably already have this secret ingredient tucked in a cabinet somewhere.

Credit: MyLoupe/Getty Images

When you've put your all into growing this year's crop of tomatoes and they turn out looking just plain puny on the vine (heartbreak!), you know it's time to take action. If your tomatoes need help, you may need to turn to an unexpected source—a salty source you may already have on hand hidden in a cabinet somewhere in your home.

If your tomatoes are looking less than their best, your soil may need a dose of nutrients (magnesium and sulfur, to be precise). Where can you find that? Epsom salts. The chemical compound also known as hydrated magnesium sulfate could be the key to better tomatoes when next year's crop rolls around.

Why Epsom salts? Plants need both magnesium and sulfur. While they usually get those two nutrients from the soil, if your soil is deficient in these two particular levels, your tomatoes will suffer. When your plants are struggling, it's hard to know just what exactly is lacking in the soil, but magnesium and sulfur have been known to jump-start stronger showings in tomatoes.

To try this strategy, pour a dose of Epsom salts into the soil before planting your tomato plants. One dose, and you could be on your way to bigger, juicer tomatoes once the fruits appear. To add Epsom salts to your garden, The Grumpy Gardener recommends adding 1/2 cup of Epsom salts per gallon of water and then drenching the soil.

The Grumpy Gardener does not recommend relying solely on Epsom salts, though. He recommends using an organic, slow-release fertilizer that will provide a complete dose of the nutrients your plants need. It's all about keeping the garden care balanced and robust. Care for your tomatoes, and they'll reward you once harvest time arrives.

WATCH: Grumpy's Tips For Beginning Gardeners

Do you use Epsom salts when planting your tomatoes each year? Do they make a difference in your garden? We've also heard rumors of baking soda and aspirin working wonders for tomato plants—have you ever tried those homegrown garden tricks for your tomatoes?