When I left Arizona for the Pacific Northwest thirteen years ago, I anticipated never needing air conditioning again. Now, I sit at the intersection of an A/C and two fans, and my garden has to put up with spikes of over 100 degrees every summer. This has prompted a sad but amusing phenomenon all over the city where folks construct elaborate installations to protect their summer vegetables: umbrella statuaries and white sheets draped everywhere. In garden groups, watering philosophy is hotly debated.
But here’s the advice from experts that is actually worth following to help your summer garden survive (and thrive) in a heat wave.
Use shade cloth selectively, and smartly
First, ditch the umbrellas. Global warming means whatever weather you have this summer is likely to repeat, so it’s time to build some infrastructure for it. Sheets help a little, but what you really want is shade cloth. This black fabric should be erected like a sail over your most tender garden spots. You can buy it in various percentages of blockage. For instance, 50% shade cloth will block out 50% of the UV rays and sun, and your local garden center (or Amazon) sells it by the foot.
You do not want it touching your plants or vegetables—you need to allow air flow around them. Lots of shade cloth has grommets in the corner so you can easily tie it to trees or fences. If you lack those, pick up some simple green U posts at Home Depot and use a mallet to put them into place, or use PVC pipe and pipe straps to set up a low tunnel to drape the shade cloth on.
Knowing what to protect and what to leave to the elements is clutch, and historically, we focus on the wrong items. Most people rush to protect their nightshades, like tomates, eggplant, and peppers. While they can all get a little sunscald (it’s like sunburn), these plants thrive in the sun and heat, and should only be something you protect once everything else is protected and you have leftover fabric. They won’t pollinate in that kind of weather and may drop their blossoms above 95F, but at this time of year, that’s not the issue—preserving the fruit is.
Peas are a very short season crop. By the time the heat dome hits, they’re about done for the season anyway. And I wouldn’t bother covering annual flowers. Artichokes don’t need the protection, roses don’t care, grass will recover, lilacs, irises, peonies, and tulips are long gone by this point of summer.
What to focus on protecting
I’d start with your hydrangeas, which will literally fry in a heat dome. I’d cover your berries, which are affected two fold—the leaves get severely burnt, and your berry crop will fail due to heat scald. This is true for strawberries and blueberries, but particularly for cane berries like raspberries, blackberries, and boysenberries.
Your lettuce and cabbage are particularly susceptible, so coverage is ideal. Anything in that tender, leafy annual group would fall into this designation.
You might want to cover your cucumbers in this weather, if only to keep them pollinating and to hopefully spare them from getting bitter, since unlike other crops, they may still be fruiting.
Watering is complicated
The old trope that watering mid-day damages plants by burning them has been debunked, but there is no doubt that roots seek out water and if you surface water during the heat of the day, the roots move closer to the surface, where they risk being burnt. You want to water early in the morning, and you want to water deeply at root level, not overhead. If you water deeply enough, you may not need to water every day. You want to check the soil by sticking your finger in it and seeing if it’s dry or moist a few inches down. That’s your guide.
You can overwater, and that’s where you need to be concerned about things like cucumbers and tomatoes, because even if you keep them thriving, they may taste terrible or develop blossom rot through the heatwave. The key is consistent watering and nutrients. If you feed your plants (and you should, weekly), make sure that fertilizer is going on early in the day, watered in. Avoid surface treatments during a heat wave.
The more established a plant, the more likely they are to survive
It’s unfortunate that heat waves are hitting as we transition to fall gardens, because plants that have been in the ground have established root systems to sustain them. Tender seedlings don’t have that, and need more babying. That can mean selective shading or hand-watering to supplement what your drip is giving them.
Change how you garden
If you garden, you surely know what zone you’re in, but you might not know that as a result of global warming, some places have shifted what zone they’re in. All this to say, what’s happening is not going away. When you think about how you build your garden you might want to ensure there are structures for shade and drip-watering.
It’s important to think about what you plant and where: Choose plants that are heat- and drought-tolerant. Make sure you’re really paying attention to whether the plants want shade or sun, and plant them appropriately.
Train your plants to use less water—by not overwatering, we encourage plants to establish strong root systems, and they’ll need less water as a result.
Mulch like hell
You really can’t overemphasize the importance of mulch in keeping plants hydrated and heat safe. A few inches of straw, wood chips, or any organic mulch on your beds will absolutely change your plants. It keeps moisture in the ground. Make sure any mulch is pulled away from the base of plants and trees so it doesn’t spread disease, but otherwise, lay it on. Remember you can get free wood chips any time in areas with Chip Drop.
Don’t leave crops out on the vine
Anything that is edible should be brought in. Even crops that you usually let ripen until you’re ready to do something with them, bring them in early. Otherwise, you’re inviting them to cook on the vine. This includes tomatoes, eggplants, peppers, green beans, cucumbers, and berries. Make sure you’re getting outside to check for ripe goods every evening or morning when its cool enough.
