Red leaves are one of the most colourful elements of autumn. Leaves that turn red in spring or summer, however, may be sending out distress signals. Like out-of-season yellowing leaves, red leaves may be caused by a light problem, watering problem or soil chemistry concerns. Learn to respond to signals to keep your plants healthy and growing well. One or more problems may be stressing your plants.
What Red Leaves Mean
Red leaves signal plant stress from several different possible sources. We associate red leaves with fall, and seeing them in summer indicates that something has accelerated the ageing process in a plant. Nearly always, red leaves are followed by brown ones and leaf death unless the cause or causes can be found.
Test soil around ailing plants. Reddening leaves may indicate a lacking soil nutrient, like magnesium for geraniums. Perennial plants are particularly susceptible to nutrient problems; sitting in the same soil year after year, they deplete soil chemicals and become increasingly dependent on gardeners to provide more. An experienced berry grower, for example, assures that plans will get enough nitrogen by side-dressing them all with peat moss each spring.
Neighbours are another issue for perennial plants. Plants may function well until a new plant is introduced close by. Fertiliser intended for the newcomer can leach through the soil to the roots of its new neighbours, adversely affecting the acid/alkaline soil balance that the original plants need to function well. Hydrangeas are well known as beacons for soil pH. Flowers of some varieties turn blue in alkaline soil and pink in acid soil. Red leaves on other kinds of plants may signal a need for overall soil conditioning.
Changes in drainage or water supply can precipitate the accelerated ageing indicated by summer red leaves. Again, look beyond the plant for possible causes. Paving a gravel driveway, replacing old timbers with a new stone retaining wall and even cutting down a large tree can cause plants in the surrounding area to receive either more or less water than they need to function well.
Basic botany teaches us the link between green chlorophyll production and the sunlight that plant leaves receive. We learn also that in fall leaves do not so much change colour as they lose colour, when dying chlorophyll reveals underlying leaf pigments. What is less well known is that excessive sunlight may overwhelm chlorophyll production in the leaves of a shade-loving plant, with the result that leaves appear red. New plants may need a shadier location; established plantings may benefit from shade cloth in summers of intense sunlight.