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Updated 8 hours ago
Question: When should you fertilize azaleas and rhododendrons? Is it better to do it in the spring or the fall? What happens if you fertilize in the winter?
Answer: Azaleas and rhododendrons are very common landscape plants here in Pennsylvania, probably due to their evergreen nature and beautiful flowers. They make terrific foundation plants, and when grown in the right conditions, they're easy to care for.
In their native habitats, both azaleas and rhododendrons are understory shrubs, meaning they much prefer full to partial shade conditions, especially during the hot afternoon hours. They are not a good choice for areas of the landscape that receive full sun. When planted in full sun, azaleas and rhododendrons often suffer from infestations of an insect pest called lacebug. To grow the best azaleas and rhododendrons, site them properly.
Another thing these two plants have in common is their need for acidic soil. Azaleas and rhododendrons grow best in woodland areas with a soil pH between 4.5 and 5.5, so even when you're growing them as a landscape plant, this pH requirement is necessary. If your soil's pH is not optimal, these two plants will show it with leaves that turn yellow between their leaf veins (called interveinal chlorosis), slow growth, and reduced flowering.
If you test your soil and the pH is optimal, and you're growing these plants in well-drained soil that's high in organic matter, fertilization is seldom necessary. But, if soil test results come back informing you that your rhododendrons and azaleas do, in fact, need to be fertilized, choose an acid-specific granular fertilizer, such as HollyTone, to do the job.
Fertilization of these plants is best done in the early spring, just before they flower and enter a period of active growth.
Fertilizing in the late summer or autumn generates new, late-season growth that's susceptible to damage from freezing winter temperatures because it does not have time to harden-off before frosts arrive.
Winter fertilization should be avoided as well. Since the plant is not in an active state of growth during the winter, most of the nutrients are likely to run off before they can be absorbed by the plant the following spring. It would likely be a waste of your money and time.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control” and “Good Bug, Bad Bug.” Her website is jessicawalliser.com. Send your gardening or landscaping questions to email@example.com or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.
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