Waterlogged soil can lead to iron deficiency
|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.
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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For week of Dec. 3:
Make the most of gaps between raindrops. This is a busy month!
* Windy conditions brought down a lot of leaves. Make sure to rake them away from storm drains.
* Use those leaves as mulch around frost-tender shrubs and new transplants.
* Rake and remove dead leaves and stems from dormant perennials.
* Just because it rained doesn't mean every plant got watered. Give a drink to plants that the rain didn't reach, such as under eves or under evergreen trees. Also, well-watered plants hold up better to frost than thirsty plants.
* Prune non-flowering trees and shrubs while they're dormant.
* Clean and sharpen garden tools before storing for the winter.
* Brighten the holidays with winter bloomers such as poinsettias, amaryllis, calendulas, Iceland poppies, pansies and primroses.
* Keep poinsettias in a sunny, warm location. Water thoroughly. After the holidays, feed your plants monthly so they'll bloom again next December.
* Plant one last round of spring bulbs including daffodils, crocuses, hyacinths, anemones and scillas. Get those tulips out of the refrigerator and into the ground.
* This is also a good time to seed wildflowers such as California poppies.
* Plant such spring bloomers as sweet pea, sweet alyssum and bachelor buttons.
* Late fall is the best time to plant most trees and shrubs. This gives them plenty of time for root development before spring growth. They also benefit from fall and winter rains.
* Lettuce, cabbage and broccoli also can be planted now.
* Plant garlic and onions.
* Bare-root season begins. Plant bare-root berries, kiwifruit, grapes, artichokes, horseradish and rhubarb. Beware of soggy soil. It can rot bare-root plants.
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