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Webpage Feature

Helping Plants Handle Summer Heat

2011-07-01

Frog taking cover from summer heat
Watering wisely helps greenery handle high temperatures

Plants cool off just like we do, by shedding water from surface areas. But with temperatures in the triple digits in Texas and many other states, evapotranspiration might not do the trick by itself. Andrea DeLong-Amaya, horticulture director at the Lady Bird Johnson Wildflower Center, has some tips for meeting plants' watering needs during the Dog Days of summer.

DeLong-Amaya notes that the biggest concern she hears is people not knowing how much to water. If you've "gone native" and installed plants or turfgrass that grow naturally in your area and are adapted to the regional climate, you usually can water less than if you have exotic plants that originated elsewhere. Still, native plants can vary greatly in their watering needs, and where they're located matters. Here are her tips for keeping your outdoor greenery going strong.

  • Learn the water needs of plants and take that into consideration when buying new ones and watering your yard. To explore U.S. native plant watering needs and other traits, visit http://www.wildflower.org/explore/. Also pay attention to which plants in your yard dry out quicker because of being on a hill, in full sun or for other reasons.
  • Once established, many native and adapted plants will do fine with watering once or twice a week during the peak of summer. A deep watering is best so water reaches plant roots and encourages them to grow deeper, making plants more drought-resistant. The soil layer nearest the surface dries out faster than deeper zones. One inch of water applied during each watering is usually appropriate, and can be confirmed with a rain gauge.
  • Soil can behave like a sponge, where water sheets off of it at first until it starts absorbing the moisture. If soil is very dry, watering twice in one day may be necessary: the first watering saturates the soil, making it more receptive to a second sprinkling. Then allow the soil time to dry before the next watering. Leaving the soil soaked for days encourages growth of fungi and other microbes that damage or kill plants.
  • If you have drip irrigation or soaker hoses installed below ground, you likely save water by getting it right to the roots. The water also won't be exposed to the evaporative heat of hot air. But if you water from a hose or overhead sprinkler, try to do so in the morning to avoid evaporation and so plant leaves have time to dry out quickly. Leaves that stay wet too long become susceptible to fungal diseases. When you do above-ground watering, consider covering the same area several times with a sweep of water if your soil tends to absorb it poorly. "Water lightly once and then go back over the plants again several times," DeLong-Amaya says.
Blade of grass with water droplets
  • Inspect plants regularly and know the signs of sun and heat-stress. If their leaves droop during the day but perk up by the next morning, they are probably fine. Drooping protects some of a plant's surface from the sun's direct rays. If brown, yellow, or white areas appear on plant leaves, that can mean too much sun exposure (they can sunburn just like we do!). A sure sign of sunburn is when leaves turn brown only on the sections in direct sunlight.
  • Droopy leaves could also signal a waterlogged plant. Be concerned if drooping lingers overnight, or plants lose color and vigor -- possible signs a plant is getting too much water. It is best to feel the soil before watering wilted plants.
  • Water potted plants more often since they have less soil protecting them from the elements and to hold moisture. Consider switching to a larger pot if a plant's roots occupy most of the space – becoming root bound. Little soil means little material to retain water in a pot. Keep in mind that a lighter colored pot in the sun stays cooler and loses moisture slower than a darker colored pot; plastic pots and glazed ceramic ones will also dry out slower than unglazed terra cotta ones. Grouping potted plants so they provide shade for each other or are in the shade of other plants can help overcome these container issues. DeLong-Amaya also recommends saucers to hold water under potted plants and extend the watering interval. Be careful that the plant doesn't stay in a wet saucer for too long, though.
  • Drinking water is costly to produce. If you are not using gray water or rainwater on your lawn, your pocketbook and the environment would benefit from letting your lawn go dormant (brown) during the summer -- assuming you have something like Buffalograss (a native grass) or Bermudagrass (an exotic) that recovers from this. You can also consider starting a new lawn from scratch consisting of a mix of native grasses indigenous to your region, as is being tested for southwestern states at the Wildflower Center.

DeLong-Amaya will discuss ways to protect the roots and leaves of heat-stressed plants in an upcoming feature on the Wildflower Center home page.

By Barbra Rodriguez

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