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'Yellow' azaleas may be linked to December storms

Waterlogged soil can lead to iron deficiency

Sacramento Digs Gardening
BY Debbie Arrington PUBLISHED JAN 12, 2022

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)

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.

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Keywords:

Sacramento chlorosis weather iron deficiency gardening chelated iron azaleas waterlogged soil rainfall alkaline soil perennials pH levels winter

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Garden checklist for week of Aug. 2

Get out early in the morning and monitor your garden’s moisture needs. Deep water and add temporary shade structures for plants that are feeling a little burned. In particular, protect developing peppers and eggplant.

* Put off fertilization until this heat passes; plants need to concentrate on hydration instead of growth.

* Harvest tomatoes, beans, squash, pepper and eggplants to prompt plants to keep producing. Give your plants a deep watering twice a week, more if planted in containers.

* Watch out for caterpillars and hornworms in the vegetable garden. They can strip a plant bare in one day. Pick them off plants by hand in early morning or late afternoon.

* Mulch can be your garden’s best friend – it conserves moisture while blocking out weeds. But don’t let mulch mound around stalks, stems or trunks. That can promote rot.

* Pinch off dead flowers from perennials and annuals to lengthen their summer bloom.

* Pick up after your fruit trees. Clean up debris and dropped fruit; this cuts down on insects and prevents the spread of brown rot.

* Prepare for a fall full of flowers by paying a little extra attention to your garden. Cut off spent blooms from roses, annuals and perennials. Roses will rebloom about six to eight weeks after deadheading.

* Indoors, start seedlings for fall vegetable planting, including bunching onion, cabbage, broccoli, cauliflower, kale, radicchio and lettuce.

* Sow seeds of perennials in pots for fall planting including yarrow, coneflower and salvia.

* In the garden, direct seed beets, carrots, leaf lettuce and turnips. Make sure to keep seeds and seedlings consistently moist.

* Plant potatoes.

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