Summer can come so suddenly! And an unexpected heatwave can spell disaster for your veggies, and for some decorative plants too. It’s good news for peppers and eggplants, true, but lettuce, spinach, all your Brassicaceae and peas too, high temperatures are a real stress! But it’s not so much the sultry air that gets them flagging, as the overheated soil!
For this reason, you need to prepare for hot spells of weather, and if, like me, you are sweating already – you need to act fast! But how can you cool down the soil in your garden? Thankfully, there are a lot of simple ways to protect plants from the hot sun. With a few preventative and protective measures, you can easily help your garden survive a hot spell with minimal impact.
So, how can you cool down the soil in your garden when the temperature soars? If you’re already sweating just thinking about it, it’s time to act quickly! Fortunately, there are many simple ways to protect your plants from the intense sun. With a few smart moves, you can help your garden survive a heatwave with minimal impact.
What Do We Mean by Hot Soil Temperature?
When temperatures reach the 80s and 90s Fahrenheit, (high 20s and 30s on the Celsius scale), it is starting to get hot. But keep in mind that soil temperature is usually lower than air temperature. However, this may depend on many factors, and it is on these that we need to act, to keep the roots of your veggies and flowers cool.
When soil gets too hot, it messes with the plant’s chemical activities, slowing down their growth. High soil temperatures make it harder for plants to absorb water and nutrients, which are essential for their health and development. As a result, plants struggle to perform basic functions, leading to stunted growth and other stress symptoms.
How Do I Know That My Plants Are Feeling the Heat?
The first signal that your plants are telling you that it’s too hot is flagging, when leaves go limp, also called wilting, or technically, plasmolysis. At this stage, if they are still green, you can still save them.
Of course, if you wait, they will dry up…
Another telltale sign is wilting. This occurs when a plant doesn’t have enough moisture, leading to reduced water pressure within its structure. Nonwoody annuals and perennials are particularly susceptible. While many plants recover when temperatures drop, prolonged wilting can cause lasting damage. If you notice plants wilting during the hottest part of the day but recovering in the evening, they are likely experiencing heat stress.
Some plants, especially those with large leaves like squash and pumpkin, may develop dry leaf edges. This is a survival tactic where the outer edges of the leaves dry up to conserve moisture while keeping the rest of the leaf functional. Although it can look similar to disease symptoms, it’s actually the plant’s way of coping with heat.
High temperatures combined with poor air quality can lead to ozone damage. This is common in areas with frequent air inversions, such as the Klamath Basin. In tomatoes, for instance, you might see dry brown spots between the leaf veins, which can be mistaken for bacterial leaf spot but lack the yellow halos. In cucumbers, squash, and pumpkin, ozone damage makes the leaves appear bleached and dry.
Extended heat exposure often causes many ornamental plants to shed their buds and flowers. This helps them conserve resources for the essential parts of the plant. This phenomenon is common in peppers, squash, and cucumbers, but these plants usually return to normal production after the heatwave passes.
Finally, bolting, or premature flowering, can occur in cool-season vegetables due to high temperatures. Plants like cilantro, broccoli, cauliflower, lettuce, and spinach are particularly prone to this. If a heatwave is predicted, it’s a good idea to harvest these plants to ensure the best quality and flavor.
1: Protect Your Plants from Heat with Mulch!
You should have done it long ago, but if you haven’t yet, mulch all your heat intolerant crops and decorative plants! This is the easiest and most permanent and long-lasting action you can take to cool down the soil.
Mulch has two effects:
- It insulates the soil from high as well as low temperatures, and temperature changes,
- It keeps water in the soil, therefore keeping it fresh as well!
Check it out with a soil thermometer, where you have mulched it will be a good 10 degrees lower than where you haven’t, even with a thin layer!
2: Keep the Soil Cool Watering Frequently
Frequent watering will help you cool down the soil. And, true, we should irrigate in the evenings, but during a heatwave you can break the rule.
In fact, if your plants flag, the first thing you need to do is water them, no matter what time of the day it is.
If you expect a very hot day, water your heat intolerant plants in the morning! I know, it will consume more water, but you risk losing your crops. Still, you don’t need to worry about heat tolerant varieties, so don’t irrigate the whole garden…
3: Water Deeply to Keep the Soil Cool, and to Train Your Plants!
We gardeners say one thing, “If you shallow water, you get shallow roots.” What does it mean? Ok, that the radical system doesn’t grow deep, but let’s remember that the soil temperature gets cooler as we go deeper… And that the first moisture to evaporate is in the surface levels.
So, keep this in mind, if you live in a hot country; train your heat intolerant plants to grow deep roots by deep watering them!
4: Water Your Potted Plants from Below to Keep the Soil and Their Roots Cool
Potted plants are in real danger when a heatwave hits. Those you have in your garden have the advantage that soil distributes the heat, and it compensates for it, while containers can’t. On top of this, they receive heat from all sides, sometimes even from the bottom…
Well, if it gets too hot, instead of irrigating your potted plants from above, water them from below! This way, the soil will suck up all the water it can hold, and their roots will have plenty to drink and they will keep fresh. Even better, get a big tray or tank, and leave them in fresh water (not too cold, you don’t want to stress them) for half an hour.
5: Shade Your Heat Intolerant Plants to Keep Them and the Soil Cool
A good way to protect your plants from overheated soil is to shade them. You can use a shading net, a 50% shading capacity will do, so, some light gets through, but not enough to heat up the ground. Alternatives can work as well, but make sure you don’t rest them straight on your veggies or decorative varieties.
Support the net with a frame, even some stakes and sticks, so that air circulates underneath.
For stronger plants, you may want to shelter them at the peak of the heat, from midday and into the late afternoon, but you can let them enjoy the morning sunshine. For weak varieties, like lettuce and spinach etc., you want to leave the net (or shading) on all day long till the heatwave is over.
6: Give Your Plants a Barrier Against Strong Sunshine
An alternative, especially for taller plants, is to put a barrier to their west. This will stop the sunshine from reaching them at the peak of the day, and, in case you can add one to the south.
But what could be a good barrier? Of course, a hedge, a wall, a fence… But they take time to grow or build… Do you want a very simple one? Cardboard! It’s cheap, light, it fully blocks the sunshine, and you can place it and remove it quickly!
And it also has insulating properties!
Keep Your Plants’ “Feet” Cold and Save Your Harvest from a Heatwave!
So, here we go, 6 easy ways to cool down the temperature of the soil when the summer heat, or a sudden heatwave hits. Act now, act quick, and you will sweat less, and so will your plants – and that will save your crops!
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