Native Plants

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Tuesday - March 17, 2009

From: Wharton, TX
Region: Southwest
Topic: Non-Natives, Compost and Mulch, Shrubs
Title: Yellow leaves on non-native pittisporum in Wharton TX
Answered by: Barbara Medford

QUESTION:

Green pittisporum that I planted 2 years ago and 1 year ago are getting a lot of yellow leaves. Variegated pittisporum that I planted at the same 2 times are doing fine.

ANSWER:

Pittosporum is a group of plants native to China, Japan and Australia. As such, they are out of our range of expertise at the Lady Bird Johnson Wildflower Center, where we specialize in the use, care, and propagation of plants native not only to North America but to the area in which they are being grown. However, yellowing of the leaves, referred to as chlorosis, can occur in native as well as non-native plants.

Chlorosis is a yellowing of leaf tissue due to a lack of chlorophyll. Possible causes of chlorosis include poor drainage, damaged roots, compacted roots, high alkalinity, and nutrient deficiencies in the plant. Nutrient deficiencies may occur because there is an insufficient amount in the soil or because the nutrients are unavailable due to a high pH (alkaline soil). Or the nutrients may not be absorbed due to injured roots or poor root growth.

If the soil is not draining well, the roots will be inhibited from picking up the trace elements in the soil, especially iron, and that will result in the plants becoming chlorotic. The major cause of chlorosis is a deficiency of one of the essential micronutrients such as iron or manganese. This deficiency occurs not because the nutrients are lacking in the soil but because they are unavailable due to alkaline soil. At these higher soil pH levels (6.5 and above) many trees and shrubs are incapable of taking up adequate amounts of iron or manganese. Central Texas has a lot of alkaline soil; however, some compost mixed into the soil or used as a top dressing often will address the problem, providing better drainage, reducing the alkalinity and improving the texture of the soil and permitting access to the trace elements needed.