Weather-Forecasting Flowers: Which Plants React to the Weather

Folk wisdom has long said that if dandelions close in the daytime and pine cones on the ground tighten up, rain is coming. These signs really are linked to plant behaviour, but plants do not forecast the weather days ahead. They react to what is happening right now: air humidity, light and temperature. Here are the most sensitive plants and what botany says about them.

Flowers in any weather: tulips and chrysanthemums.

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How it works

• Humidity. Some plant tissues swell in moist air and shrink in dry air. Pine cone scales open in dry weather to release seeds and close when it is damp.
• Light. Many flowers close when light levels drop, on overcast days and in the evening, protecting their pollen from damp and cold.
• Temperature. Tulips and crocuses open in warmth and close in the cool, because the inner and outer sides of the petals grow at different rates at different temperatures.

Botanists call these movements nastic responses. Before rain, humidity usually rises and clouds thicken, so plants “signal” a change in the weather, but after the fact rather than in advance.

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The best-known “forecasters”

• Scarlet pimpernel, known in England as the “poor man’s weatherglass”: its small red flowers close in dull, damp weather.
• Dandelion: the flower heads close in the evening and under heavy cloud and open in bright light.
• Pot marigold: open in sunshine and closed on overcast days.
• Wood sorrel: folds its leaves in dim light and when touched.
• Clover: folds its leaflets in the evening and in dull weather.
• Pine and spruce cones: open in dry air and close in damp air, something you can watch at home.

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Folklore and science

Many folk weather signs rest on sound observation: plants really do respond sensitively to humidity, light and warmth. But flower-based forecasts only work for the next few hours and depend on many factors. For weekend plans, a weather forecast is more reliable, while watching “living barometers” makes a fun walk. More folk beliefs in “Flower superstitions”.

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Try it at home

Put a dry pine cone in a bowl of water: after a while the scales close, and once it dries out they open again. This simple experiment shows how nature’s “hygrometers” work. More fascinating plant facts in “Interesting facts about flowers”.

FAQ

Can a plant predict rain in advance?

No, it reacts to conditions that have already changed: rising humidity, less light, cooler air.

Why do flowers close at night?

To protect pollen and nectar from dew and cold; they open again in the morning for pollinators.

Author: Maria Svitlovir

Graduated from Taras Shevchenko National University of Kyiv, Institute of Biology and Medicine (2001). BSc in Biology, MSc in Horticulture. Writes about plants, works at a garden centre selecting and repotting plants, and contributes to plant reference guides.

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