Hollies, with their lush, evergreen foliage, beautify the garden during all four seasons. Add berries for Christmas, and you have one of the most generous plants in the garden. Hollies--usually easy to care for--sometimes require a little TLC. Usually bright and green, holly leaves sometimes turn yellow, often signaling a cultural problem. Chlorosis, one of the more serious holly ailments, is often the cause of yellow leaves.
Chlorosis shows itself on hollies by all-over leaf-yellowing. Leaves start to lose their deep green color and glossiness. The severity of chlorosis determines how yellow the leaves will become. Pale green coloring of leaves can last months or even a few years. Severe cases can turn leaves completely yellow and kill a holly in one season.
Chlorosis is caused by iron deficiency. Even though iron may be present in the soil, holly trees cannot take it in unless the soil is slightly acidic. Yellow leaves lack green chlorophyll, necessary for photosynthesis.
Hollies with chlorosis can be treated by regular fall feedings of acid-loving tree-and-shrub fertilizer, according to label instructions. For a shot in the arm, spray with chelated iron, which turns leaves green quickly. Scratch iron sulphate into the soil for a long-term solution. Annually top-dressing the soil with an inch of compost and pine bark will add acidity over time.
Hollies like moist, well-drained soil rich in organic matter. The ideal pH is between 4.5 and 6. When planting, mix in lots of compost to increase acidity. If existing soil is alkaline, mix in iron sulphate to lower pH. Replenish mulch each year. As it breaks down, it will slightly acidify soil. Fertilize annually with fertilizer formulated for acid-loving plants.
Yellow leaves do not always signify chlorosis. Hollies, like many evergreens, shed about one-third of their leaves in the spring. Leaves turn yellow first before falling off. This is normal. Spring leaf drop should be followed by fresh, green growth. Bright yellow leaves can be a sign of water-logged roots. Hollies in wet soils should be transplanted to well-drained locations.