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The case of the Copper Beech, pursuing the color purple

  • Anne-Marie Walker
  • Acer palmatum (Japanese maple) is a purple focal point gracing this home’s entry. Remember to practice fire-safe landscaping.
    Acer palmatum (Japanese maple) is a purple focal point gracing this home’s entry. Remember to practice fire-safe landscaping.
    In the gardens of Blenheim Palace, Winston Churchill's birthplace in Oxfordshire, England, there stands an immense Copper Beech, Fagus sylvatica "Purpurea." The tree is at once majestic and dramatic in large measure because of its bronze leaves amid an otherwise very green, leafy garden. It begs the question of why some plants have bronze, red, or purple leaves and how these leaf colors intensify landscapes.

    In the case of the Copper Beech, bronze, coppery, and purple leaves were traced to a genetic mutation that occurred around 1450 CE. Ever since, the prevalence of Copper Beech has increased due to human selection. In other words, red-leafed trees and plants draw us presumably because they are different, and as landscape designers are quick to point out, purple plants give depth to our gardens and make edges visually seem to disappear. Put another way, choosing to accent with the color purple makes our garden spaces feel less flat.

    Loropetalum chinense gives depth as a focal point in this planting bed.
    Loropetalum chinense gives depth as a focal point in this planting bed.
    Plants are truly amazing. Anchored in place, they absorb light and transform and channel this energy to form chemical bonds that make energy-rich food molecules called carbohydrates. This is the chemical process by which plants feed themselves. Called photosynthesis, it literally translates to "light put together." The leaves of plants have pigments, including chlorophyll, xanthophyll, and beta-carotene, that help capture light. When the dominant pigment is chlorophyll, the leaf is green. If the plant has purple leaves, the dominant pigment is anthocyanin, the same pigment found in red and purple foods like strawberries and blueberries. As daylight hours and temperatures decrease, signaling the end of the growing season, production of the dominant pigment chlorophyll decreases. Low temperatures and bright sunshine cause the destruction of chlorophyll such that when dry sunny days are followed by cool, dry nights, we get fall color. When this occurs, leaves turn red, purple, and yellow and fall from trees.

    Purple-leafed Heuchera ‘Plum pudding’ begins its long bloom cycle adding pizazz to this planter.
    Purple-leafed Heuchera ‘Plum pudding’ begins its long bloom cycle adding pizazz to this planter.
    Plants with high anthocyanin levels gain protection from excessive light and some protection from pests and predators while still having to produce enough chlorophyll to thrive. Exploring this balance, scientists have observed that the concentration of anthocyanins can be influenced by several factors, including mutation, hybridization, and environmental conditions, including light, temperature, and soil. Here are some helpful tips when planting purple-leafed plants. First, make certain there is sufficient light in the area you select to plant a purple-leafed plant because insufficient light may cause purple leaves to turn green. If this occurs, give the plant more sun, and barring interference from high temperatures, you will likely see purple leaves again. Second, review the temperature range in your garden because purple leaves seem to do better in cooler conditions, which allows increased anthocyanin accumulation. High temperatures reduce the accumulation of anthocyanin. A combination of low temperatures and high light will often produce the darkest purple leaves. Lastly, assess your soil, paying close attention to the levels of iron and magnesium, which support the function of absorbing sunlight during photosynthesis. Attention to these three factors will help ensure your purple-leafed plants thrive.

    There is a long list of bronze, purple and red-leafed plants that grow happily and successfully in our Marin gardens, including Heuchera 'Plum Pudding' (Coral bells native to California), Dodonaea viscosa 'Purpurea' (Purple hopseed bush good for screening), Prunus cerasifera (Flowering plum), Loropetalum chinense (Fringe flower that blooms early), Cotinus coggygria' Royal Purple' (Smoke bush), Acer palmatum (Japanese maple with light, green bark), Phormium tenax purpureum (Flax), Penstemon' Midnight Masquerade' (Beard tongue that's a drought tolerant native and attracts hummingbirds) and succulents like Aeonium' Purple Queen'. There is quite a world of purple-leafed plants waiting to be discovered and introduced to your garden. Get ready to intensify your landscape!

    Photos: Anne-Marie Walker