'Yellow' azaleas may be linked to December storms

This azalea shows signs of chlorosis in its new growth. Waterlogged soil likely kept the plant from accessing iron in the soil. (Photos: Debbie Arrington)

Waterlogged soil can lead to iron deficiency

By Debbie Arrington

Are your azaleas looking a little peaked? It may not be a lack of nutrients, but too much water.

Cindy Nalepa-Nelson, an observant longtime gardener, noticed yellowish growth on azaleas in her Land Park garden. In a walk around her neighborhood, she spotted several other examples of azaleas that were showing telltale signs of chlorosis, or yellowing of normally green leaves.

Usually, this yellowing is a sign of iron deficiency. But that doesn’t mean there’s not enough iron in the soil. Due to soil conditions, the plant’s roots couldn’t access that iron when the bush needed it for green, chlorophyll-packed leaves.

Cindy wondered if the yellow leaves could be linked to recent rain, particularly December’s deluge. According to UC Cooperative Extension master gardeners, the heavy rain likely did play a role. But it didn’t leach out the iron; it waterlogged the soil.

“Azaleas, citrus, gardenias, rhododendrons, and other plants that are adapted to acidic soil are especially prone to iron deficiency when soil pH is above about 7.5 (alkaline),” say the master gardeners. “Iron deficiency is also common when soils are cool, high in calcium, poorly drained, or waterlogged.”

Here's another azalea with chlorosis. Notice the green veins

in the yellowish leaves.

Plants can’t access iron (or several other nutrients) when their roots are standing in water. Azaleas – especially older foundation bushes – may be stuck in spots with less than ideal drainage such as next to the house, in concrete beds or under trees. If the bushes stay waterlogged, that can lead to crown rot and death.

Iron deficiencies tend to be more common in clay soils; the iron becomes “locked” in the soil and unavailable for plant roots.

Other signs of iron deficiency: Stunted or malformed new growth; mottled yellow leaves with green veins; and bud or fruit drop. Leaves may develop brown margins, too.

Because azaleas are shooting out new growth now, those yellowish leaves are more noticeable.

To remedy the problem, aerate the soil. Poke holes to encourage drainage. Add compost or other organic matter to help drainage as well as the soil’s acidity.

Then go ahead and feed those yellowish azaleas with chelated iron, a form of this nutrient that’s easily and quickly absorbed by plants – even in clay soils. Chelated iron is available at nurseries and home centers.

For more about iron deficiency in plants, check out these UC integrated pest management plant notes: http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISORDERS/irondeficiency.html.