Tomato plants struggle during the sweltering days of North Carolina summers, but they aren’t the only garden crops that suffer when temperatures soar. Squash, beans and pepper plant growth and production can also slow to a halt during this dead heat — but you can do a few things to lessen the damage and maybe even get to pick some ripe fruit off the vine.

For our N&O Summer Desk series, we talked to Ashley Troth, an agriculture expert with NC State Extension’s Durham County Office, for guidance. (This interview, presented as a Q&A, has been lightly edited for clarity.)

Q: Why does the heat impact our tomato plants?

A: We think of tomatoes as being hot weather vegetables, but they don’t actually want it that hot. They’re really happy around 75 to 80 degrees, and with even cooler nighttime temperatures than that, they would just be happy all the time and produce really well. But the big problem is that anytime they start experiencing more than 85 degrees during the day, or even more than 70 degrees at night, which is what we’ve been having, they have trouble pollinating their flowers properly.

The flowers form, but if they experience those higher temperatures in about a two-day window after the flower opens, they won’t pollinate quite right. So you’ll go out and see flowers, but they’ll yellow and almost just drop off. The plants are struggling to produce the energy they need, and the hotter it gets, the harder they’re working.

High temperatures prevent proper energy production, but they also require the plants to metabolize more. They can start shutting down, just saying “I can’t handle any of this. If I’m even going to stay alive, I can’t worry about reproduction.”

Q: Why do tomatoes have trouble pollinating in the heat?

A: Tomatoes are largely self-pollinated, mostly from the wind jostling it around. They can be helped along by bees, but it’s mostly that jostling. At high enough temperatures, the flowers will abort (or die). At slightly higher temperatures than that, around 100 degrees, the pollen doesn’t even grow well. So if the pollen landed where it needed to be, and even if the flowers didn’t abort, the pollen wouldn’t be able to spur fruit like it usually does.

Plus, when temperatures are above 90 degrees, a lot of pollinators don’t like to pollinate as much because they’re also trying to beat the heat. So certain crops, like peppers, won’t have the pollination they need, so you might get misshapen fruit or even reduced fruit.

If our temperatures start coming down a bit, we can get everything to work itself out.

Q: That means tomatoes won’t form from the plants’ flowers?

A: Maybe not ripe ones. Even if that tomato were able to set fruit at that high temperature, they actually can’t produce a lot of the red pigments over 85 or 90 degrees. So even if the fruit is there, you’ll see them just sit on the vine green for a really long time.

It’s because they can’t kind of do the final part of ripening. A lot of us are already impacted from the drought, but the people who got lucky and have some tomatoes might just see them sit on the vine green until the temperatures start coming down from below 85 or so.

Q: Can you pick your tomatoes green and ripen them off the vine?

A: Yes, but only if they already have a bit of red pigment. This is called blushing, and it’s a common method to ripen larger tomato plants. Usually the smaller varieties, like cherry and even grape, ripen quickly on their own.

But in this extreme heat, you can pluck them when they’re a bit red and put them in a paper bag to speed up the ripening process. If you don’t see any red and you’re just picking a hard green tomato, it won’t ripen at all.

The other one-two punch of this is that the lack of water means they’re struggling even more, and you’re more likely to get problems like blossom end rot where the ends of the fruit turn black and start rotting.

Q: Will manually watering the plants help prevent that?

A: It’s really a symptom of inconsistent watering — a symptom that the soil is drying out a lot in between watering. So if you can get out there and be really consistent with your watering — don’t drown them every day, but give them enough water every day or every other day — it also helps cool the soil.

Q: Can consistent watering help tomatoes produce even with temperatures over 85?

A: It definitely might. Anything you can do to cool it off and give it the resources it needs, even on just part of the plant, will help the whole thing. Applying a little bit of mulch around your tomatoes can be really helpful. That can help cool the soil which can help even help the roots

Now, that’s not going to help you in terms of the flowers pollinating, but it means that if any could pollinate properly, the plant will have an easier time maturing that fruit. You should also make sure you’re staying on top of removing diseased and damaged leaves and plant tissue. That’ll help too.

Q: What about shade?

A: A bit of shade can definitely help. But like always, you’re playing a delicate game. Especially a bit in the afternoon, when the sun is the harshest, could really help.

If your tomato could pick, it would want morning sun to feel really good. Around 2 p.m., it wants nothing to do with it. That’s when that sun gets really hot and hard for them.

For myself, last year I had tomatoes in pots in a spot that I thought was actually annoyingly shady. But they loved it because they weren’t just baking. I was really worried that I only got only four or five hours of direct sun, but I think that other shade was just enough that it took the edge off. I think we all feel that way, tomatoes included.

Q: Which other summer plants have issues in extreme heat?

A: Unfortunately, there are a number of garden plants that can have this trouble pollinating. We can see it in peppers, in beans and even in squash. Beans start dealing with this when temperatures are over 95, which we’ve already experienced a bit this summer.

Another way we see this is that a lot of squash produce both male and female flowers. The way you can tell them apart is a male flower has a really thin stem supporting it, and a female flower has a thicker, fat stem which will become the zucchini. In these high temperatures, they tend to produce more male flowers, so you’ll go out and see a squash plant absolutely covered in flowers, but no zucchini will come. So this is your time to practice your fried squash blossom recipes, but the squash itself might not be a part of the meal.

Q: Which summer garden staples love this heat?

A: Herbs! This is the time to shine for some of our Mediterranean herbs. Rosemary is super happy, doesn’t care about this heat.

The tender-leafed stuff like basil might need some more water, so keep watering them and they’ll be happy too. But make sure you’re watering at the base, because that’s when we can get into some more diseases. But they love this weather, this is their moment to succeed.

Q: Are we at the halfway point of the season?

A: If it stays hot like this, then absolutely. August is always hard for us, and July we expect to be a little better. But if it stays hot, it might just be a bad season. Which is unfortunate, of course, but it just sometimes happens.

And it’s a great moment to explore your local farmers market! You can always count on them to have the beautiful stuff that home gardens might just not in tough growing seasons.

Q: At what point do you give up and take your summer plants out of the ground?

A: As long as the plant isn’t too diseased, we should keep with it. The weather might turn around, which I say as an optimist. When you’re a gardener, you’re an optimist.

But we also know from a soil health perspective, it’s better to have living plants in the ground than to have bare soil. I’d rather have a not-too-diseased tomato sitting in the soil than having it bare and open, because even a decently healthy tomato is still giving sugars from its roots, which feeds and protects the soil.

So if you look at that thing and it’s really yellow or completely fallen over or extra dried out or wilting, then yeah, rip it out. But if it’s just limping along, let it go and just keep it where it is. Plus, we can’t plant anything else until it cools off anyway. I only take things out to put another thing in.

Q: When do we look ahead to the fall garden and those planting dates?

A: In September, but when in September depends on the previous season. If it’s super hot, then it’ll be later than usual. But we’re too early to make that determination. We start thinking about planting dates for the cool season in August.

Need gardening help? How to ask the Raleigh/Durham experts

The NC State Extension office has an Extension Master Gardener program in each of the Triangle’s five counties. Get connected to your county’s program by phone or email, and a master gardener volunteer can help troubleshoot and offer solutions for free.

Visit sites.google.com/ncsu.edu/garden-questions/home to find your best point of contact.

This story was originally published July 5, 2024, 10:48 AM.