Give ming aralia water and warmth

Q: My ming aralia looked lush and healthy until it suddenly started dropping leaves. It's near an east-facing window and gets lots of bright morning light, and I have watered twice a week. What could be wrong? -- Kirsten Andersen, Wheeling A: Overwatering, cold temperatures and a high concentration of soil salts are the common reasons why established ming aralias (Polyscias fruticosa) will suddenly drop leaves. Ming aralias need to be watered thoroughly, but only after their soil becomes dry. The twice-weekly schedule that worked in spring and summer might be too frequent in fall and winter, when ming aralias grow slowly, if at all, and usually need less water. How often they need to be watered will depend on your conditions, including amount of light, room temperature and how moisture-retentive the soil is. Because they are tropical plants, ming aralias are happiest when temperatures are above 60 degrees. Since your plant is growing close to a window, be sure the drapes are closed at night, or pull the plant farther from the window so it's less likely to be in too-cold air. If you or the grower fertilized with tap water high in sodium or with softened water, or the plant has been fertilized frequently, it's possible that salts have built to damaging levels in the soil. Consider switching to watering with rainwater or distilled water, and don't fertilize again until new growth resumes. If new growth doesn't appear in spring, flush the current soil with water to leach any remaining salts, and then replant in new potting soil that is light and fast draining. As long as leaves are green, ming aralias usually need only light fertilization. Fertilize three times a year (spring, mid-summer and early fall) with a dilute mixture of water-soluble fertilizer, or once in spring with a slow-release fertilizer. Finally, unlike some other aralias that need very bright light, ming aralias will tolerate bright to moderate light, but they must have higher humidity, a condition that is harder to maintain in winter. Low humidity alone probably wouldn't have caused your ming aralia to suddenly drop leaves, but it might have added to your problem.
Robin Carlson, Chicago Botanic Garden
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