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Over the Fence

Where gardeners come to find out what's happening out in the yard.

Yellow Leaves That Should Be Green

Posted by Richard Hentschel -

Down the Garden Path

Richard Hentschel, Extension Educator

Have you got a tree or shrub with leaves of yellow that are normally green in your landscape? Chlorosis is a common problem in some years and in lots of situations, temporary depending on what causes it. Leaves can be completely yellowed, a mottling of green and yellow or just showing green along the veins in the leaf. If the chlorosis is long lasting, expect to see marginal browning and leaf tip dieback. Later those browned cells drop away leaving a tattered looking leaf.

If the condition has been caused by weather, the symptoms should go away as the changes in the weather become more stable. In the spring, cold wet soils can influence nutrient uptake by the plants and cause a yellow of the leaf tissue as young leaves are developing. As the plants are able, they will catch up and turn a leaf that is slightly yellowed green again. Some trees will naturally lose some of those first leaves that emerge as more leaves develop. Birch is a good example. The resources from those early leaves are moved to the leaves at the growing point where they can be more effective. These leaves that are lost are often much smaller than normal too.

When most homeowners hear the word chlorosis, it usually means a condition where a nutrient in the soil is lacking or the plants inability to absorb that nutrient in a timely fashion during a period of rapid growth. The more common nutrient is iron. Iron is involved with the chlorophyll molecule in the leaf. There can be a number of different colored pigments in the leaf, but in this case it is the green color and that chlorophyll molecule produces photosynthates that in turn are returned to the root system for growth. So a plant that is suffering from chlorosis is also not producing the much needed food for healthy growth. A good example of a plant that routinely has chlorosis is a Pin Oak. Pin Oak really needs a more acidic soil pH than is typical in our area. Our alkaline soils make it very difficult for a pin oak roots to absorb iron from the soil.

Homeowners have some remedies that are fairly easy. Be sure your soil has a pH range of between 6.0 and 7.0, 6.0 to 6.5 is even better. This will allow the plants to absorb the iron they need naturally. If you suspect iron chlorosis, there are products on the market that can be sprayed on the leaves. If iron is the problem, a leaf will turn green in 24 to 48 hours. Spraying the leaves helps, yet you are treating the symptom and need to work on the cause by adding organic matter which is naturally acidic or consider using elemental sulfur to adjust the pH of the soil. Organic matter works pretty well on smaller plants. Sulfur can be applied with an inorganic fertilizer containing sulfur or by itself. Sulfur is an element and by itself is considered organic. Be sure to apply enough to allow for a pH change for a couple of years.



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