How to Help Your Plants Survive a Heat Wave

We are going through one of our typical mid-spring heatwaves where temperatures soar into the upper 90’s and plants struggle to stay hydrated. Rather than a gradual climb, it is normal for our temperatures to suddenly spike making it feel like late August rather than late April. This sudden increase in temperature can be really hard on plants as they haven’t had time to acclimate to the rising temperatures.

// ]]>Especially sensitive are those that have been recently planted and haven’t had time to establish a nice, deep root system. Although we prefer to retreat into the our air-conditioned homes on such days, spending just a little time, especially in the early mornings or cooler evening caring for our plants can make the difference between whether or not they survive. Here is what you can do:
1. Water. Obvious yes? Well, not exactly. How and when you water really matters during a heatwave. Watering in the early morning or late evening means plants can take up moisture before the heat evaporates it from the soil. Watering deeply, especially for trees and shrubs, allows water to get down to the lowest portion of the roots. If your plants need water midday, then by all means give them some. But don’t just assume that wilting leaves mean a plants needs water. During particularly hot days, water evaporates from the leaves faster than plants can take it up from the roots. This can be especially true of large-leafed plants like rhubarb, for example. Before you turn on the hose, stick your finger in the soil near the plant. It will often still be wet just below the surface and watering now will just waste water and can actually cause problems.
2. Move pots and hanging baskets to shadier locations. Those full,FLOWERS OUTSIDE THE CAMDEN HEAD lush hanging baskets can almost be impossible to keep watered during hot, windy days. The best thing you can do is take them down and place them in a location where they will get morning sun until the weather cools down. Moving other container plants to a shadier location will make your watering chores easier. I like grouping my water-needy pots in one area, preferably near a hose, so I can easily water them when needed which is sometimes two (even three if it’s really hot) times a day.

If your hanging pots become really dry, soak them in a bucket to rehydrate them. What often happens with hanging baskets is the potting mix will actually shrink away from the edges of the pot. When you  water the basket,  it runs down the side of the pot and out the bottom without actually hydrating the rootball itself.

3. Add some temporary shade. Newly planted plants or those with large, tender leaves really struggle when it’s hot. Giving them some temporary shade during the hottest part of the day can help them survive. Putting in four stakes around a plant and draping some shade cloth over the stakes can greatly reduce mositure loss from plant leaves. Moving patio furniture is another solution. I’ve temporarily moved plastic chairs to cover newly planted crops of lettuce when the weather gets hot.
4. Mulch. If you haven’t done so already, add a good 2″-3″ layer of mulch around your plants. Not only does it help suppress weeds and reduce moisture loss, natural mulches like bark or straw help keep roots cool.
5. Check your drip systems. The high mineral content in our water can quickly clog drip emitters making them useless. Plants that might have been getting by with water from the neighbors may not make it during hot weather. Make sure to flush your system and check that every emitters is flowing smoothly. And instead of turning on your drip system an additional day, spot water those plants that seem to be in need.
6. How to tell which plants need water. Most plants do give off signs that they are stressed due to lack of water, but the signs are often subtle. Normally when a plant’s leaves start to wilt it has been struggling for some time. Before wilting, leaves tend to look a bit dull and lose their sheen. Hard leafed plants will often start to curl their leaves just a bit to try and reduce more moisture from being lost. Also keep in mind what your plants normally need. Plants that like to stay moist really need to stay moist. And newly planted transplants will still have that tiny root system about the size of the container they came out of. Pay particular attention to these plants.
7. Don’t fertilize plants during a heatwave. Plants that are dry can take up too much fertilizer at one time which will cause their leaves to burn and could even kill them. Wait until temperatures drop to fertilize.
8. Don’t immediately prune off wilted growth. Dry, wilted growth if often still protecting the rest of the plant. Pruning it off before temperatures drop could cause even more damage. Watch the weather reports and wait a week or two to clean up heat damaged plants.
Hanging basket photo by Stephen McKay [CC-BY-SA-2.0], via Wikimedia Commons

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2 comments for “How to Help Your Plants Survive a Heat Wave

  1. Peggy A
    at 7:24 am

    Thanks for the information, I learned something new. Sometimes the warm temps catch me by surprise after our wet winters in Seattle. I’ll be taking your advice this year.

    • Kat
      at 10:37 am

      I hope it helps. Our weather here is pretty unpredictable in spring. After our heat wave, we dropped to about 60, then next week back in the high 80’s. The plants, and the gardeners, get so confused.

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