Weather extremes can have negative effects on plants. Growers of horticultural crops need to be prepared. They use shade nets to protect plants from damage caused by hail and sunburn. The color of shade nets can affect plant growth and development. Heuchere are perennial plants. In a three-year experiment, we found out how color affects the growth and flowering of three species of heucheras, as well as the content of plastid pigments and phenolic compounds. The experiment was conducted in four treatments where we covered the Heucheras with green, black and blue netting, the control had no netting. The higher daytime temperature on clear and cloudy days was higher under the blue net than under the black one. Plants of orange cultivar 'Cassandra' were tallest under the blue net in the black net, purple cultivar 'Shanghai' was taller underthe black net, green 'Lime Marmalade' was tallest under the black net in the green net. The nets had no effect on flowering. The blue net transmitted the least amount of light, as indicated by PPFD measurements and spectrum measurements. The content of carotenoids was higher in the plants under the nets. We detected 27 different phenolic compounds and classified them into 5 groups. The content of phenolics was higher in the plants under the blue net.
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