Predicting the Weather With Plants

Look to These Plants for Your Daily Forecast

September 12, 2021
Pine Cones

Many plants can predict the weather! Look no further than the trees, flowers, and grass in your own garden for cues about impending rain and other weather events. Here are more than 20 weather-predicting plants which are known to be good forecasters.

While we use satellites and sophisticated technology today to forecast the weather, you can do what farmers and many others have always done.  Look to the skies, consider the behavior of birds and animals, and also look to our plant life! Yes, plants! 

Watch for Weather-Predicting Plants

Humidity and Rain

  • In a pine forest, your friend is the pinecone. While not a traditional bloom, the pine tree’s cone is believed to be one of the most reliable precipitation prognosticators. They change shape according to whether it is wet or dry! In dry conditions, a cone’s scales stand separately and stiffly; in dampness, the scales soften a bit and close up to assume the cone’s familiar shape.
     
  • Also, look up at the leaves of oak or maple trees. These leaves tend to curl in high humidity, which tends to precede a heavy rain. Just like frizzy hair does! 
     
  • If the small white flower of common chickweed, or stitchwort (Stellaria media), is closed, this means that rain is close at hand. In dry weather, it is regularly open from about 9:00 in the morning until noon. 
     
  • So it is also with the purple sandwort and the scarlet pimpernel. They open in sunny weather, but close tightly when rain is expected. The latter, also known as the “poor man’s weatherglass,” closes when the air’s humidity reaches about 80! Hence, we have this adage.

Pimpernel, pimpernel, tell me true,
Whether the weather be fine or no.

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  • On the other hand, don’t put too much faith in Tragopogon pratensis (aka yellow goat’s beard or Jack-go-to-bed-at-noon), as this sleeper does indeed nod off, regardless of the weather.
     
  • When the African marigold opens later than 8:00 a.m. or closes before 5:00 p.m., rain can be expected.
     
  • Keep an eye, too, on morning glory blooms: Wide-open flowers are a sign of fair weather, but closed petals indicate that rain or bad weather is on the way.

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Morning glory. Credit: Borchee/Getty Images

  • The common daisy will close its petals as rain approaches and not allow a single drop in; sometimes the petals will even droop downwards. When the weather if fair, however, they’ll keep their petals open. This happens because the upper surface of the petal grows faster at higher temperatures than the lower surface of the petals. Rain cools the temperatures, which encourages the underside to grow faster, and making the petals close up. The same thing happens at nighttime.
     
  • Many other flower varieties close their petals as rain or night approaches, to open them again after the rain or on the next morning—germander speedwell, hieraciums, red campion, succory, tulips, white water lily, wintergreen, and wood sorrel, to name a few. 
     
  • If any of the following open later or close earlier than their usual times, watch for rain: daylily (opens at 7:00 a.m., closes at 7:00 p.m.); dandelion (opens at 7:00 a.m., closes at 8:00 p.m.); lettuce (opens at 8:00 a.m., closes at 9:00 p.m.).
  • If you see dew on the grass at sunrise, this indicates clear weather for at least a few hours; in warm weather with clear skies, the loss of surface heat drops the temperature down to the dew point.  But if the grass is dry, there’s a good chance of rain clouds. 

When grass is dry at morning light/
Look for rain before the night.

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Changing Temperatures 

  • Rhododendrons have an amazing ability to act as a temperature gauge. Their leaves will unfurl as it gets warmer. They will be closed at 20 degrees by when the temperature is above 60, the leaves are open!  See if you notice!

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Watch for these signs—just some of nature’s weather indicators—and keep an eye out for others, too. You never know what you’ll notice.

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Reader Comments

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Rhododendron leaf curl!

I noticed the leaf response to cold right away. For my specimen, and in this area of NY, the leaves curl at around 25 degrees. Very cold winter nights, leaves can be nearly completely closed, then open if the afternoon "warms" to about 30. Leaves will also curl when the plant needs a drink during rain-free hot summer weather. I'm sure the amount of water the plant is getting in winter slightly changes that temperature range for the leaves to open and close.