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A soap or oil spray will turn your blue spruce green.

Warning: horticultural oils (dormant oil, summer oil, etc.) and soaps (insecticidal soap, dishwashing soap used as a pesticide, etc.) will melt away the bloom that covers the leaves of many conifers, hostas and other plants: the waxy white powder that gives them their blue coloration. These products have the same effect on the bloom that covers many fruits (blueberries, grapes, plums, etc.). So if you spray your blue spruce or your blue hosta, their leaves will turn green! And you will see your blueberries go from blue to deep purple! The effect is not harmful, but it can be disappointing.

Fortunately, the effect is temporary. No, the discolored leaves and fruit will never regain their original color, but the new ones that grow back the following year will be as blue as they ever were.

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

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