Why are my tree’s leaves turning yellow in summer?

Summer yellowing can be a dry spell, a soil problem, or something more serious. Where the yellow sits, and which leaves it hits, tell you a lot.

Green leaves turning yellow in June or July is a tree telling you something. It might be as minor as a dry spell, or as serious as a disease in the wood. Two clues narrow it down fast: where the yellow sits on each leaf, and which leaves on the tree are affected.

Sometimes it’s normal

In dry summers, tulip trees and river birches yellow and drop some of their older, inner leaves to cut their water use. That isn’t a sign of decline, and watering helps (University of Tennessee; Purdue Landscape Report; Iowa State University Extension). If whole limbs or the whole tree changes color, or branches die back, look for another cause (Purdue Landscape Report). See why trees lose leaves in summer for more on drought drop.

Yellow leaves with green veins: chlorosis

When a leaf turns yellow but its veins stay green, the usual cause is a shortage of iron or manganese. It starts with leaves that are lighter green than normal and can progress to bright yellow, then to small, nearly white leaves with scorched edges that drop early. Oaks are usually short of iron, maples more often of manganese (The Morton Arboretum).

The soil usually has plenty of both. The problem is high pH: in alkaline soil, trees can’t absorb them. Iron and manganese are generally most available in slightly acidic soil, around pH 6.0 to 6.5 (The Morton Arboretum). In more alkaline soil, iron in particular becomes less available above about pH 6.5 (University of Maryland Extension). The ideal pH varies by species, and trees prone to chlorosis include pin oak, red maple, white oak, river birch, tulip tree, sweetgum, bald cypress, and white pine (The Morton Arboretum). Drought and girdling roots can cause the same pattern (UMass Amherst).

What to do: start with a soil test to confirm the pH. The longest-lasting fix is better rooting conditions: replace turf under the tree with 3 to 4 inches of mulch and water in dry spells. Trunk injections, done by a certified arborist, last two to three years, while leaf sprays fade within a few months (The Morton Arboretum). Lowering soil pH is slow and doesn’t last, since alkaline soils drift back, so for new plantings the best approach is choosing a tree that suits the soil (Michigan State University Extension).

Old leaves or new leaves?

Some nutrients can move inside the plant, and some can’t. When a tree runs short of nitrogen, phosphorus, potassium, or magnesium, it pulls them from older leaves to feed new growth, so the older leaves yellow first. Iron, manganese, zinc, and other nutrients that can’t move show up first on the newest leaves (University of Delaware Cooperative Extension). Either way, test the soil before you fertilize (University of Delaware Cooperative Extension; University of Maryland Extension).

Too much or too little water

In drought, young trees often yellow, then brown, wilt, and lose their tips (University of Florida IFAS). Too much water looks surprisingly similar: in waterlogged soil, roots run short of air and the tree yellows, wilts, and browns as if it were dry (University of Kentucky). Check the soil a few inches down before adding more water.

Root problems

Trees planted too deep, or buried under added soil, often show yellowing, leaf scorch, early leaf drop, and stunted growth; the telltale sign is a trunk that goes straight into the ground with no flare at the base (Montana State University Extension). Roots circling and squeezing the trunk cause a thin crown and early color (University of Maryland Extension). Roots cut or crushed in construction often show up as sparse leaves, scorch, or early fall color on the damaged side, sometimes years later (University of Maryland Extension). Newly planted trees can yellow and wilt from transplant shock for two years or more (Purdue Extension).

Diseases in the wood

Yellowing that hits one branch or one side of a tree, with leaves wilting and the branch dying, is a warning sign. Verticillium wilt does this to maples, ashes, lindens, catalpas, elms, redbuds, and others; peeling back the bark on an affected branch often shows brown or green streaks in the wood. It can’t be cured (University of Wisconsin–Madison Extension).

On elms, leaves that wilt, curl, yellow, and brown, often starting at branch tips, can mean Dutch elm disease (UNH Extension). On oaks, oak wilt turns red oak leaves bronze and brown from the edges inward, often from the top, and can kill a tree within weeks; to reduce the risk of spreading it, avoid pruning or wounding oaks during the high-risk season. In much of the Upper Midwest, that’s April through July (Iowa State University Extension), and in Texas, February through June (Texas A&M Forest Service), so check local forestry guidance before pruning. Bacterial leaf scorch browns leaf edges in mid to late summer, sometimes with a yellow border, starting on the lower, inner, older leaves, unlike drought scorch, which starts at the top (University of Maryland Extension). All of these need a professional diagnosis.

Tiny pests

Leaves that look finely speckled before turning dull yellow may have spider mites, which thrive in heat, especially around pavement (NC State Extension). Lace bugs leave yellow-to-white speckling on top of the leaf and black, varnish-like spots underneath, on oaks, sycamores, and other trees (Utah State University Extension). See what’s damaging these leaves? for a full guide.

Weed killer drift

If leaves are twisted, cupped, or curled rather than simply yellow, suspect lawn or roadside weed killer that drifted onto the tree (Montana State University Extension). Trees usually survive a single drift, but give them a full growing season before judging recovery (UT Extension).

Quick clues

• Green veins, yellow leaf: iron or manganese chlorosis; check soil pH.
• Oldest leaves yellow first: a mobile nutrient such as nitrogen, or normal drought shedding of inner leaves.
• Newest leaves yellow first: iron or manganese.
• One side of the tree: root damage on that side, or verticillium wilt.
• Scattered branches wilting on an elm or oak: Dutch elm disease or oak wilt; call an arborist.
• Speckled leaves: spider mites or lace bugs.
• Twisted or cupped leaves: herbicide drift.

When in doubt, your county extension office can help identify the problem from a sample, and a certified arborist can inspect trees near homes and driveways.