With summer temperatures climbing higher each year, many gardeners suddenly find it harder to grow tomatoes. Plants that used to burst with fruit come July now seem stuck. Thankfully, an inexpensive garden tool – shade cloth – means we can still grow beautiful and juicy tomatoes even in the middle of a heatwave.
Okay, first off.
All you southern gardeners can quit sniggering at those of us further away from the equator. We’re in uncharted territory here. (But also, thank you for figuring all of this out already. We appreciate it.)
When the Heat is Less Than Ideal
Believe it or not, it can get too hot for tomatoes. I know, I know. We’ve all been led to believe that everyone’s favorite veggie to grow is all about that hot summer sun. But, like all plants, tomatoes do best when grown in their ideal temperature range. Anything outside of that, and weird stuff starts to happen.
Specifically – no or slow tomatoes.
Heat stress can slow plant growth down to a crawl, and it can put an end to fruit production. It makes sense when you think about it. Most of the plants we grow in our gardens will go into self-preservation mode, eliminating unnecessary processes to conserve water and energy until the temperatures cool again. If you want to zoom in on the issue a little more, it mainly has to do with certain chemical processes that happen within the plant. All of these have ideal temperature ranges in which they occur.
A big one for tomatoes is the production of ethylene.
Ethylene is what causes the ripening process in tomatoes. It’s a signaling hormone, meaning its presence in the fruit kicks off a variety of other naturally occurring changes in the ripening process, such as the production of lycopene and carotene, both of which give tomatoes their characteristic ripe hue.
The ideal temperature to grow tomatoes is between 65-85 degrees (that’s daytime air temperature, by the way). Once you get above 85 degrees, things begin to slow down. When temperatures sore into the 90s and 100s, tomato blossom set and fruit ripening all but stops as the plant goes into survival mode.
Shade Cloth to the Rescue
And that’s where shade cloth comes in. This magical stuff cuts the sun’s rays, effectively shading and cooling the plants growing beneath them. Depending on where you live and the type of weather you get, you may only need to use shade cloth periodically during extreme heatwaves. But when added to your normal tomato care routine, it can keep you growing during the hottest weather.
We northerners are used to dealing with the opposite end of the spectrum – covering our tomatoes to protect them from frost.
Well, this is the same thing, just on the higher end of the thermometer.
Above, Not On
Rather than draping the cloth over your plants like you would for frost protection, you want to suspend it above the tomatoes. This keeps the plants cool and, more importantly, helps to cool the soil around them as well.
Soil Temperature is Important Too
Speaking of soil temps. If you’re going to use shade cloth, then you need to do it right. That means mulching around your plants as well. As you can see in the photo below, the bare soil gets baked during the day, and it holds that heat even at night. That’s 105F soil on a day that was 92F.
Mulching helps to keep the soil beneath it cool and locks in the much-needed moisture your tomatoes will also need to thrive during these hot spells.
Repeat after me: apply shade cloth, apply mulch. They really do go hand in hand.
What Percentage to Use
When purchasing shade cloth, you’ll likely be treated to a range of shade percentages: 75%, 60%, 50%, 40%…and so on. It’s a bit as confusing as picking out an SPF when buying sunscreen.
Luckily, the Rural Sprout readership has plenty of southern gardeners who were willing to help. The consensus seems to be that between 50% and 40% is what you should be aiming for. From my personal experience, 40% seems to be right on the money. After all, I’m not dealing with the same temperatures as my southern friends. As the saying goes, your mileage may vary.
Alternatives to Shade Cloth
While shade cloth is incredibly effective, there are a few good alternatives to consider in a pinch.
Light Colored Sheets
Now, I’m not talking about your good 800-count Egyptian cotton sheets. No, no, you want that set of 200-count sheets you got as a wedding gift from your cheap uncle that are collecting dust in the back of your linen closet. The lower the thread count, the more light and air can pass through. After all, we’re shading our tomatoes, not blocking the sun out entirely.
Beach Umbrellas
Oh yes, once you’re done with your day at the sea or the lake, you can use your umbrellas to shade your tomatoes. Because these are quite a bit more opaque than shade cloth, you’ll want to use them sparingly or only during the hottest parts of the day.
An Added Bonus – Avoid Sunscald
Another benefit of using shade cloth (or one of its alternatives) is that you’ll avoid sunscald. Yep, your tomatoes can get sunburned too. (Honestly, I’m not all that surprised. I look like a tomato every time I get sunburned. So why wouldn’t the reverse be true?)
During especially hot weather, direct sun can burn tender young tomatoes as they ripen. You’ll notice white or yellowish blisters on the sides of tomatoes. These blisters become thin and papery and often rupture, leaving the fruit to rot on the vine.
While sunscald is most common in unripe tomatoes, if it’s hot enough, it can also affect mature tomatoes.
One of the best ways to prevent sunscald is proper pruning. (Which is why pinching back all those tomato suckers isn’t always the best thing to do.) Tomatoes, despite being sun-loving plants, rely on the leaves to protect the fruit from too much direct sun exposure.
Along with pruning your tomatoes you can use shade cloth when it gets hot as h-e-double-toothpicks out there to protect your ‘maters.
Managing a heatwave can be tough on gardens and gardeners alike, but thankfully, we’re a pretty ingenious lot that always comes up with a solution to keep on growing. With regular care and the addition of some shade cloth, you can still grow a bounty of tomatoes.
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