Garden Detective

Garden Detective: Dogwood not happy amid landscape conversion

The leaves of this pink dogwood indicate possible chlorosis, or iron deficiency.
The leaves of this pink dogwood indicate possible chlorosis, or iron deficiency.

Q: There’s a problem with the leaves on my pink dogwood. The tree is about 25 years old and is large and has been very healthy. It gets sun and dappled shade. Our soil here in River Park is great. We recently removed our turf and replaced it with new landscaping including drought-tolerant plants, hardscape and a drip system. Could that be causing the problem? In May, I gave the tree some 30-10-10 water-soluble fertilizer, which I have done every spring after it blooms. I’ve also noticed it did not form berries this year even though it was in full bloom this spring. What could be causing this?

Gayle Abbott, Sacramento

A: According to UC master gardener Annie Kempees, your dogwood tree has issues that may have to do with change in watering practices, soil type, potential iron deficiency and the fact you have an acid-loving plant.

Because our rainfall last winter was so sparse and sporadic and most people don’t water their large shrubs and trees in winter, lack of winter moisture may cause some plants to hold off producing berries, flowers and/or leaves. Dogwoods require deep watering, twice a month, all around the dripline (the outside edges of the leaf canopy). On drip irrigation, a dogwood tree needs a total of six to eight emitters evenly spaced around the dripline. Speak with irrigation professionals for the correct size emitters to ensure the dogwood has enough water to survive the ongoing drought.

Is your dogwood getting enough water? See how far the water is penetrating the soil. At the beginning of this process, water the tree well, taking care to avoid watering near the trunk; water out at the dripline and slightly beyond it.

Use a narrow shovel and dig into the soil within and out past the dripline to determine how deep the water is penetrating into the soil; 18 to 24 inches down is a good rule of thumb.

A layer of mulch 3 to 4 inches deep within the root zone, keeping it 4 to 6 inches away from the trunk, will help retain moisture, keep weed seeds from getting a strong hold and keep the soil cool in the heat. Dogwoods are not particularly drought tolerant; when young and not yet established, most of their genus (Cornus) prefer weekly water. Mature trees do well if given deep watering twice a month.

Most components of soil in the Sacramento area are very slightly acidic to neutral (6.5 - 7.0). Acid-loving plants such as your dogwood prefer a moderately acidic soil (5.0 - 6.0) to thrive. When dogwoods are not growing in drought conditions, an acid-based fertilizer may be used.

The photo you sent gave a visual sign that your tree may be chlorotic, indicating an iron deficiency. This may mean your dogwood needs iron. Iron deficiency is usually caused by alkaline soils or those that are very wet, or have drainage problems. In a healthy plant, most of the leaves are green. In leaves with iron deficiency, veins are green, and the areas between the veins of young leaves have changed to light green or yellow. As the chlorosis increases, the leaves may become smaller, taking on a whitish cast and have dead margins and tips. Twigs die back and defoliate as the deficiency increases.

Iron deficiency can be corrected by acidifying the soil or using iron fertilizers, according to package directions.

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