Gardening: My city is turning into a desert for a week
June 24, 2021 4:55 PM   Subscribe

Starting this weekend, we are going to have what, for us, is a pretty freaking extreme heatwave. At least 6 days of temperatures around/above 30 degrees celsius and possibly getting up to 38 (99 degrees fahrenheit). It's a dry heat. The sun will be beating down, no clouds. Help me save my plants please.

I am not sure if I can rig something up to protect them. I have different flowers sprinkled across a large area. I think the perennials will be ok, as will my vegetables, but I am particularly worried about my young Asters and Zinnias, which I grew from seed. They are actually North-facing but we get sun from the East, North and West all day. They get 12 (?) hours of sun this time of year and they have had a rough start (I grew them from seed, foolishly let them get wind and sun burnt when hardening off...) They are only just starting to show signs of good growth about 3 weeks after being transplanted. But now this is about to happen. Ideas, please? The cheaper the better? Sprinkler when the sun is highest (water is expensive, though)?. Also, my tomatoes. Although they are together in one spot and I can probably easily rig up a bedsheet over them.
posted by kitcat to Sports, Hobbies, & Recreation (12 answers total) 6 users marked this as a favorite
Water your tomatoes before or at sunrise and as long as they don't dry out they'll be fine. A week of flirting with 40 is normal for my area and tomatoes in the ground are fine without extra precautions.
posted by Mitheral at 5:02 PM on June 24, 2021 [9 favorites]

Best answer: It may be too late to get shadecloth locally, which is really want you want to use for this. All my garden centers have it on industrial-sized rolls and you just ask for so much of it, even the big-box hardware stores have it by the garden center doors/checkout stands - you might go tonight and see if you can get some.

Do not water while it's over 90 degrees, they won't drink and it can increase the ground heat and humidity in the immediate vicinity. Actually getting water on them will cook them. Water deeply as early in the morning as you can, and ideally only water the ground and keep the foliage as dry as possible.

Without shadecloth, yes use sheets or old light-colored t-shirts or whatever you can use to tent them from overhead sun but still allow as much airflow as possible at ground level. You can also use umbrellas if you can anchor them so they don't blow away, either actual weather umbrellas or the patio type if you can drag them into a spot to provide some kind of shelter from midday on. If any of your flower beds are up against a house or similar, you could make cardboard lean-to shelters to make shade but you're going to have to be concerned about airflow too.

Some plants just will give up when sensing those kinds of ambient temperatures, no matter what you do or how protected from the sun they are. They'll just be like ope, my season is over now I guess, byeeeee.
posted by Lyn Never at 5:05 PM on June 24, 2021 [8 favorites]

Best answer: Maybe a tunnel of garden fabric like this:

I use something similar to protect seedlings I planted too late in the spring; it could protect from the worst of the sun and keep what moisture is there inside the tunnel.

I make the hoops with lengths of narrow PVC pipe, they are a few dollars each or big box home improvement stores.
posted by acantha at 5:06 PM on June 24, 2021 [1 favorite]

These are normal summer temperatures where I live, although we have higher humidity most (not all) of the time. We do fine with the "standard" vegetables you'll find in a "standard" garden, like tomatoes, squashes, and so on. As well as lots of different types of flowers. Some of these plants were started from seed and put out when it was quite hot.

We've already had several days in a row of weather this hot and sunny, and our zinnias are doing fine. Great, actually. We don't have any asters but haven't had trouble with them before.

Your plants should be fine as long as you follow the previous advice and water them deeply in the morning. The main thing is not to wait - you want them to be very well hydrated before the heat hits. Water the ground, not the leaves - water can magnify the sun's rays and scorch the plant.

If you miss a morning watering and your plants start to wilt, watering in the afternoon is better than not watering at all. However, you might need more water (it will evaporate faster) and it's more important to keep the water off of the leaves.

Tbh, we almost never use shadecloth even when we should. Sometimes the tops of our tomatoes get slightly burnt, and this is our biggest "heat" issue. I'm guessing you don't have any ripening tomato fruits yet, though, and that's when you really have to start worrying about it.

If your seedlings are super small and delicate you might want to rig some shade over them (like a sheet or something), but it might not even be necessary.
posted by Kutsuwamushi at 6:03 PM on June 24, 2021 [1 favorite]

Best answer: Sprinkle very late at night or first thing after dawn. Definitely don't do it when it's hot -- around noon or the afternoon is the WORST time, because the water will evaporate before it hits the plants, and won't have a chance to soak into the ground.

In very bad droughts, we put a hose on our mature trees at a constant trickle all day and all night, and ignore all the other (cheaper, younger, replaceable) plants. But if your trees are safe and you're trying to save your perennials, I'd honestly set the sprinkler for like 2 a.m. and let it do its thing if it's 80*F/25*C at night. Plants where I live are used to dire humidity during the daytime, and if it's 80*F at night, they're not going to develop mold from being wet. (Also it rains here in the night in the summer, all the time.)

If I lived somewhere were plants got very sensitive about nighttime moisture, I'd set my sprinklers for 4 or 5 a.m. and cross my fingers. But if it's getting that hot during the day, it should dry up most molds and fungi that want to grow on the plants.

But a constant trickle on mature trees is THE most important thing for the urban environment!

But yeah, never sprinkle when the sun is highest, then you're just paying for evaporation.
posted by Eyebrows McGee at 6:26 PM on June 24, 2021 [2 favorites]

Just want to emphasize again that you want to water deeply now, before the heat wave starts. Make sure your flowers are well hydrated before the heat kicks in.
posted by bluedaisy at 8:24 PM on June 24, 2021 [6 favorites]

Also, my tomatoes. Although they are together in one spot and I can probably easily rig up a bedsheet over them.

Tomatoes love heat to grow giant plants. They don't love heat for setting fruit, so they probably won't set any flowers while it's hot but plant-wise they will be fine. They'll set fruit again when it gets colder.
posted by The_Vegetables at 7:51 AM on June 25, 2021 [2 favorites]

Zinnias do very well here in central TX where we have months of 100F+ dryish heat. If they're already well established from your planting 3 weeks ago you will probably keep them through this heatwave. Like everyone else said, you've got to water everything early in the morning (or late at night).
posted by fiercecupcake at 8:48 AM on June 25, 2021

Best answer: We're about to have a pretty bad heat wave in my town, and here are tips for plants as published in my local paper.
posted by bluedaisy at 9:38 AM on June 25, 2021

Best answer: Mulch? We've been getting hot and dry temps for two weeks now. I put down some straw around the bases of the plants. On the advice of a master gardener friend, I also covered the stone and brick walkways between the garden rows with a layer of wood chips.
posted by olopua at 9:40 AM on June 25, 2021

Seconding mulch. We heavily mulch under all our plants(wood chips for perennials, straw or marsh hay for veggies) and that keeps the soil moisture way up while also slowly breaking down and adding nutrients to the soil.
posted by rockindata at 10:45 AM on June 25, 2021 [1 favorite]

Thirding mulch. It is essential for moisture retention in soil, and acts as an insulator against both heat and cold for the roots.
posted by spitbull at 2:34 PM on June 25, 2021 [1 favorite]

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