Signs of a Sick Magnolia Tree in Arlington, Texas

Most sick magnolias in Arlington have the same problem

Southern magnolia is a beautiful, appropriate tree for North Texas with one significant caveat: it wants slightly acidic soil, and Tarrant County's runs alkaline — commonly pH 7.8 to 8.3 over the Fort Worth Prairie. At that pH iron and manganese are chemically present but biologically unavailable.

The result is iron chlorosis, and it is by a wide margin the most common magnolia complaint we see. The signature is unmistakable once you know it: leaves turn yellow between the veins while the veins themselves stay distinctly green. Newest growth shows it first and worst.

Chlorosis versus actual disease

Yellow between green veins → chlorosis

Soil chemistry, not a pathogen. Treated with chelated iron — soil-applied for mild cases, trunk-injected for severe ones — plus, longer term, sulphur or acidifying amendments to move the root-zone pH. Do not reach for general fertiliser; it does not address the problem and the nitrogen can push soft growth a stressed tree struggles to support.

Uniform yellowing, oldest leaves first → normal, or nitrogen

Magnolias shed a flush of old interior leaves every spring. Yellowing on the oldest leaves only, with the canopy otherwise fine, is usually just that.

Black sooty coating on leaves → scale insects

Sooty mould grows on honeydew excreted by magnolia scale. The mould is cosmetic; the scale is the actual pest. Treat the insects and the black disappears over a season. Look for small bumps on twig undersides.

Brown or black leaf spots, especially after a wet spring → fungal leaf spot

Usually cosmetic on an established magnolia. Rake up and dispose of fallen leaves, improve air movement with careful thinning, and avoid overhead irrigation.

Wilting whole branches, dark streaking in the wood → verticillium wilt

Soil-borne, no cure, and the tree may or may not compartmentalise it. Reduce stress, remove affected wood, and do not replant a susceptible species in the same spot.

Culture beats chemistry

• Magnolias hate wet feet. Check drainage before adding water.
• Keep the root flare exposed — buried flares rot, and magnolias are often planted too deep.
• Mulch out to the drip line if you can; magnolias resent lawn competition and string-trimmer damage.
• Do not over-prune. Magnolias flower on the previous season's wood and heavy cutting costs you bloom for years.

If the leaves are yellow with green veins, you very likely have a soil problem with a straightforward fix. Our Arlington diagnosis visit is free and we will tell you which of the above you are actually looking at.