The extreme heat in metro Phoenix isn’t leaving any time soon, so make your peace with it. From getting burned by your seatbelt buckle to constantly being sweaty, it's the price we pay for living here the rest of the year when the weather is lovely.
But humans aren't the only life forms that struggle in the excessive heat we're experiencing this summer.
Gardeners know what I’m talking about. From sunburned plants and heat-stressed trees to wondering when and how to water your lawn when the thermometer hits 118 degrees for days in a row, people are concerned about keeping their plants alive this summer.
Here's how to care for plants during extreme heat.
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Why are my plants dying in the heat?
There are many reasons why your plants could be dying in the heat, including not being in the shade enough or water stress.
The University of Arizona Cooperative Extension's website says that "extreme heat is a form of stress and will negatively impact plant health."
Here are some common reasons why plants may be dying in the heat, according to the Cooperative Extension:
- Water stress: High temperatures cause plants to lose water quickly through a process called transpiration. If the rate of water loss exceeds the plant's ability to take up water from the soil, it can lead to dehydration and wilting.
- Root damage: In hot conditions, soil can become dry and compacted, making it harder for roots to absorb water and nutrients.
- Heat stress: Extremely high temperatures can disrupt the plant's metabolism and overall functioning.
- Sunburn: Some plants are more sensitive to direct sunlight, and intense heat can cause sunburn on leaves and stems.
- Lack of shade: If plants are not provided with adequate shade during the hottest parts of the day, they may be exposed to too much direct sunlight, increasing the risk of heat-related damage.
- Soil quality: Poor soil structure and lack of organic matter can contribute to decreased water retention and nutrient availability for plants. You can start doing a homemade compost bin to help.
- Plant selection: Some plants are better adapted to handle heat than others. If you've chosen plants that are not suited for your climate or weather conditions, they may struggle to survive in extreme heat.
How do I keep plants alive in extreme heat?
"Do not plant or prune plants during intense heat," said Michael Chamberland, assistant agent for urban horticulture at the University of Arizona Maricopa County Cooperative Extension.
Under normal circ*mstances, plants can recover quickly from pruning. But during a heat wave, it adds unnecessary stress that can put plant health at risk.
To help your plants thrive in hot conditions, consider implementing the following measures from HorticultureUnlimited.com, based in Tucson:
- Water your plants deeply and regularly.
- Mulch around the base of your plants to retain soil moisture and regulate temperature.
- Provide shade or use shade cloth during peak sun hours.
- Consider using drought-tolerant or heat-resistant plant varieties.
- Improve soil quality by adding organic matter to enhance water retention and nutrient availability.
- Use water-conserving techniques like drip irrigation to reduce water wastage.
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Should I water plants every day in extreme heat?
During extreme heat, watering your plants every day may seem like a good idea to combat the high temperatures and keep the plants hydrated.
However, watering frequency should not be based solely on a fixed daily schedule, as it can lead to overwatering and other problems. The best approach is to water your plants as needed, taking into consideration various factors that influence their water requirements.
"Plants recently planted within the last year or two may need water more frequently. Watch your plants for signs of wilt or dried leaves," said Chamberland.
Tailor your watering approach to each species in your garden. Some plants might need more water during extreme heat, while others may be better adapted to survive with less frequent watering.
Here are some guidelines from MoonValleyNurseries.com, with locations throughout metro Phoenix, to determine when and how often to water your plants during extreme heat:
- Check soil moisture: Assess the soil moisture level by sticking your finger or a trowel a few inches into the soil. If the soil feels dry at that depth, it's time to water.
- Observe plant behavior: Pay attention to your plants' appearance. If they look wilted or show signs of stress (e.g., drooping leaves), it's a sign that they need water.
- Water in the morning or evening: Watering during the cooler parts of the day helps reduce water loss through evaporation, allowing the plants to absorb more water. Moon Valley Nurseries recommends between 4 a.m. and 6 a.m. during a heatwave.
- Use mulch: Apply mulch around the base of your plants to conserve soil moisture and reduce the need for frequent watering.
- Monitor local weather conditions: Watch for potential changes in temperature or rainfall. Adjust your watering schedule accordingly.
What plants do well in extreme heat?
If you want to cultivate a garden that can withstand high temperatures, the Gilbert Public Works Department's Plants for the Arizona Desert page recommends:
- Succulents and cactus.
- Lavender.
- Rosemary.
- Hibiscus.
- Lantana.
- Zinnia.
- Yucca.
- Texas sage.
- Desert marigold.
Keep in mind that while these plants are heat-tolerant, they still need initial care and watering until they establish their root systems. Once established, they should require less maintenance and water compared to more delicate plants.
How to keep plants cool in extreme heat
Here are ways to help your plants withstand excessive heat using tips from SummerWindsNursery.com:
- Drip irrigation: Consider using drip irrigation or soaker hoses to water your plants directly at the soil level. This method reduces water waste and ensures that the water reaches the root system where it's needed most.
- Evaporative cooling: Mist the leaves and surrounding area with water during the hottest part of the day. As the water evaporates, it cools the plant's surface and the surrounding air. This will also increase humidity.
- Use reflective mulch: Reflective mulch, such as white or silver mulch, can help bounce back some of the sun's rays and reduce heat absorption around the plants. According to the Summer Winds Nursery, which has three locations in metro Phoenix, mulch "also acts as a natural substitute to fertilizers."
- Use shade structures: Install pergolas, arbors or shade sails to provide protection from intense sunlight.
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What is the best time to water plants in extreme heat?
The best time to water plants during extreme heat is early in the morning. Watering in the morning allows the plants to absorb moisture and hydrate before the temperatures rise to their peak.
"Keep in mind that hoses and water inside them will heat up in the sun.If your irrigation system turns on late at night, it is harder to see if you have leaks or problems.If you are watering by hand, early morning before sunrise can be the most comfortable time with adequate visibility," said Chamberland.
For more information on how to properly water your plants at any time of the year, go to Chandler's "Landscape Watering By the Numbers" guide.
Is it bad to water plants at night during summer?
While it's not necessarily bad to water at night, here are the reasons why watering at night can be less favorable:
- Fungal diseases: According to Moon Valley Nurseries, "Watering in the evening time, especially during moist or humid nights, will promote mold and fungal growth that can affect your plant or your tree's overall health."
- Reduced absorption: Plants absorb water more effectively during the daytime when they are actively photosynthesizing and growing. Watering at night may result in less efficient water uptake, as plants' metabolic processes slow down during the dark hours.
- Root rot: If water remains on the foliage or soil overnight, it can promote root rot and other issues, as excessive moisture can suffocate the roots and encourage fungal growth.
- Attracting pests: Dampness at night can attract slugs, snails and other pests that prefer moist environments.
Can plants recover from extreme heat?
Yes. Many plants can recover from extreme heat if they receive prompt care. The extent of recovery depends on the severity of the heat stress and the specific plant species. Some plants may suffer irreversible damage and may not fully recover.
Should I cover my plants in extreme heat?
Covering plants during a heatwave is probably not necessary if you have selected heat-tolerant varieties and provided adequate watering and mulching. However, for particularly sensitive plants or during periods of unusually intense heat, using temporary covers can offer some protection.
"Consider using horticultural shade cloth over sensitive plants," Chamberland said. "Use a light shade cloth of 30% shade (which will let through 70% of sunlight).Do not use a heavy weave shade cloth, which will block too much light.Plants need a good amount of light to grow.They can be burned by the sun if they are overshaded and the shade cloth is removed."
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