Newsflash: Summer is HOT, Even for Plants
Learn to recognize and combat the signs of heat stress in plants. Master Gardener Jennifer Deeks also shares which plants are faring best in the record-breaking heat this summer.
COMMUNITY CONTRIBUTION
A series of record-breaking high temperatures this summer has been unpleasant at best. For those of us who work outdoors or are vulnerable to heat and poor air quality, it has been sometimes dangerous. I have wilted heavily in the heat more than a few times this season!
My own gardens are curated in such a way that once plants are established, I normally don’t water them at all. I have found myself watering well-established plants, even some natives like my grey coneflowers (Ratibida pinnata).
Plants and trees are absolutely feeling the heat, and unlike humans or animals, they aren’t able to move around to seek shade or water.
Signs of Heat Stress in Plants
The most obvious sign of a plant suffering is when it wilts. Wilting is caused by water loss and can be caused by both a lack of water from poor rainfall or evaporation losses from high temperatures that exceed the plant’s ability to replenish moisture.
You may notice plants that wilt in the midday heat that have perked up the next morning, and most plants recover from short periods of wilt. You may see “leaf scorch” where leaves brown and die, most often at the tips and edges. This condition is often quite apparent on young trees.
When heat stress happens over an extended period of time, plants rely on more extreme measures — such as dropping flowers or leaves — to help reduce water loss.
It can be challenging to pick out primary heat stress signs from a number of pests and diseases. To further complicate things, plants that are experiencing heat stress are more vulnerable to attack by pests and disease, so they can have multiple issues going on at the same time.
Ways to Help
Hydrate: Water plants slowly and deeply, ideally early in the morning. A light spray of the hose will not penetrate the soil, and roots will stay up near the surface, where they are more exposed to the heat. Watering deeply encourages the roots to follow the water downwards, where they are more protected.
Mulch: A good layer of mulch will help retain water in the soil, slow evaporation, and help regulate the temperature around the roots.
Don’t fertilize: when a plant looks like it’s struggling, it can be tempting to think that more nutrients are better. When a plant lacks water, the salts in fertilizers can draw more water out of the plant. Fertilizing can also burn the roots, leaving the plant with even less ability to absorb water when it does become available.
These types of extreme temperatures and unpredictable rain events are likely to become more common as the climate continues to change. If you are planning a new garden, seek out plants that are more drought-tolerant.
I have the privilege of seeing many gardens. Some of the plants I have observed to be thriving this year under these conditions are the pale coneflower (Echinacea pallida), butterfly milkweeds (Asclepias tuberosa), the Catmints (Nepeta spp.) and (rather unexpectedly) roses of many types.
The plants that seem to be performing poorly this year include the New England asters, cup plants, and Japanese maples.
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