How To Prevent The Terrible Tomato Rot

About This Episode

A reader learns why their tomatoes are turning black on the bottom. Grumpy’s tip about reusing potting soil for growing vegetables.

Question Of The Week

"Why are my tomatoes black on the bottom?"

Grumpy's Response: Okay, my guess is that that's due to a condition called blossom-end rot, and it's caused by a soil that's too acidic. The reason they call it blossom-end rot is because the end of the tomato opposite the stem is the one where you'll see this starting. And the tomato will start to rot, and then it'll just turn black from that end and progress. And it's ugly and nasty, and you can't eat the tomato, and you just pick it and throw it away. And like I said, it happens because the soil is just too acidic. When the soil is too acidic, it prevents the plants from taking up enough calcium to build strong cell walls for the fruit. And so the fruit rots. Now, tomatoes like a soil with the pH of about 6.5. You can have your soil tested to see what it is. If a soil test shows the pH is lower than that, making it too acidic, sprinkle a cup of ground lime around the base of each plant, and that'll help. Another thing that can cause blossom-end rot is large swings in soil moisture because this can interfere with the function of the roots, and they might not function properly and, again, not pick up enough calcium. So to keep this from happening, try to keep the soil evenly moist and mulching around your plants will help do this too.

Tip Of The Week

This comes from a question that I got from a reader, and they were about ready to fill some containers and put out some new plants for the summer. And they had some old pots that had potting soil in which they had grown stuff in there last year.

They wanted to know whether it was okay to use the old potting soil again or put in fresh potting soil. My answer to that is I think you're better off taking the old potting soil and putting it into the compost, and then putting fresh potting soil in for your new plants. This is especially true if you're gonna be growing any kind of vegetable crop in containers because when you're growing vegetables a lot of them have insect and disease pests. And sometimes they can overwinter in the soil of the pot that's just sitting there all winter. If you plant the same kind of plant in there another time, you may have pest problems. Also, the potting soil tends to break down. I mean, you can have all sorts of things getting in there.

I would just start off with fresh potting soil because some of them have a little bit of fertilizer to get you going. But you could also have a fertilizer buildup in a plant that has old soil in there because some people will think it's necessary to go and fertilize every single week. So do yourself a favor. I think it's not that expensive. Take that old potting soil, put it in the compost, and then after everything is composted with all the other stuff you got in your compost bin, spread it around the garden.

About Ask Grumpy

Ask Grumpy is a podcast featuring Steve Bender, also known as Southern Living’s Grumpy Gardener. For more than 30 years, Grumpy has been sharing advice on what to grow, when to plant, and how to manage just about anything in your garden. Tune in for short episodes every Wednesday and Saturday as Grumpy answers reader questions, solves seasonal conundrums, and provides need-to-know advice for gardeners with his very Grumpy sense of humor. Be sure to follow Ask Grumpy on Apple Podcasts, Spotify, or wherever you listen so you don't miss an episode.

Editor’s Note: Please be mindful that this transcript does not go through our standard editorial process and may contain inaccuracies and grammatical errors.