Yellow leaves in summer: iron chlorosis, wet roots, drought and the normal shed
Why a tree's leaves turn yellow in July and August, how the pattern tells chlorosis from drought or soggy roots, which trees are prone, and what to do for each.
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Yellow between green veins: iron and manganese chlorosisOlder leaves yellowing in July and AugustYellow, then wilted, on wet groundA whole new tree turning yellowWhat fixes the yellowing, and what does notTrees that take limy groundWhere to startCommon questionsSourcesWhich leaves turn yellow, and how, points to the cause. Yellow between green veins on the newest leaves of a pin oak, river birch or another tree of acid ground is iron or manganese chlorosis, from soil above pH 7. Scattered older leaves that yellow and drop in July and August are the normal summer shed, which dry weather speeds. Leaves that yellow and then wilt on soggy ground mean roots short of air. A whole crown yellowing on a tree planted in the last year or two is most often transplant shock.
The pattern, read from the leaves, sorts the usual causes:
| What you see | What it usually is | Check first |
|---|---|---|
| Yellow between green veins, worst on new leaves | Iron or manganese chlorosis on alkaline soil | A soil pH test |
| Scattered older leaves yellowing and falling in midsummer | The normal shed, sped by drought | How dry the soil is |
| Leaves yellowing, then wilting, on ground that stays wet | Roots short of air in waterlogged soil | Water standing after rain |
| A whole tree yellowing in its first year or two | Transplant shock, or a tree set too deep | The root flare |
| One whole limb or the whole crown turning on an older tree | A root or trunk problem, borers or a wilt | The trunk and the ground over the roots |
Yellow between green veins: iron and manganese chlorosis
Iron chlorosis starts as pale green leaves in summer, the veins still green, and turns to a general yellowing later in the season. In bad cases the leaves come out small and nearly white, their edges scorch and they drop early. It may show on one or two branches or over the whole tree.
The iron and manganese are in the soil. Above pH 7.0 they take a form roots cannot absorb, and soils over limestone and the disturbed soils of city and suburban yards often run that high. In oaks the shortage is most often iron, and in maples manganese. Too much phosphorus, potassium or magnesium in the soil can bring the same yellowing.
Pin oak is the tree most often affected. Red maple, white oak, river birch, tuliptree, sweetgum, bald cypress and white pine yellow on high-pH soil too, and river birch begins at about pH 6.5. We do not grow red maple, tuliptree, sweetgum or white pine. These natives we grow yellow on alkaline ground:
- Pin oak yellows on alkaline ground, and the tree can die there. Zones 4 to 8, 50 to 70 feet.
- White oak takes clay, sand and dry spells, but not alkaline soil, where its leaves yellow. Zones 3 to 9, 50 to 80 feet.
- Swamp white oak yellows in alkaline soil, so it belongs on ground on the acid side. Zones 3 to 8, 50 to 60 feet.
- Willow oak yellows on alkaline soil and wants acid or neutral ground. Zones 5 to 9, 40 to 75 feet.
- River birch yellows on alkaline soil. Zones 3 to 9, 40 to 70 feet.
- Bald cypress turns its needles yellow on limestone. Zones 4 to 10, 50 to 80 feet.
- Black gum prefers acid soil and turns yellow on limestone. Zones 4 to 9, 40 to 70 feet.
- Carolina silverbell yellows between the veins on high-pH soil, and watering will not fix it. Zones 4 to 8, 30 to 40 feet.
- Sassafras yellows on limestone. Zones 4 to 9, 30 to 60 feet.
Older leaves yellowing in July and August
A tree gets rid of some older, less productive leaves in favor of new growth, and in a dry summer it sheds more. From late June through August a tuliptree drops scattered yellow leaves from all through its crown, a response to dry soil that some trees repeat every year:
“Although it can be quite striking to have your tree drop its leaves, this rarely affects the overall health of the tree.” (Purdue Landscape Report, Tulip poplar summer leaf drop)
River birch does the same, shedding leaves and twigs in late summer dry spells, and in a severe drought even an old river birch yellows and drops its leaves. Yellowing from drought usually leaves no green veins: the whole leaf turns. A deep soak over the roots in a dry spell is the answer, in the amounts that drought and an established tree gives.
Scattered leaves are the shed. A whole limb or a whole crown turning at once is something else: a root or trunk infection, borers, or injury to the trunk or roots, and it needs a closer look. Weed killer that reaches the roots can yellow leaves as well, as herbicide damage on trees explains.
Yellow, then wilted, on wet ground
Roots need air. In soil soaked by heavy rain or flooding, water fills the pore space, and roots short of oxygen stop taking up nutrients, so the leaves yellow and can drop early. The yellowing passes once the soil drains, unless it stayed wet long enough to kill roots, and then the tree must grow new ones.
Flooding in the growing season does far more harm than in winter, and some trees decline after a little over two weeks under water. Root rot moves into the weakened roots. Overwatering and mulch piled deep can starve roots of air the same way. Trees differ:
- Carolina laurelcherry yellows and dies with too much water. Zones 7 to 10, 15 to 40 feet.
- River birch takes floods of a few weeks, but not water that stands all summer.
- Pin oak takes winter flooding, but flooding through the growing season can kill it.
Let the soil dry before watering again, keep mulch 4 inches from the trunk, and find where the water stands.
A whole new tree turning yellow
A tree planted in the last year or two that yellows all over is most often short of roots, the transplant shock of its first seasons. Planting too deep suffocates the roots and yellows a new tree too, and so does too much water. Finding the root flare shows how to check whether a tree went in too deep.
What fixes the yellowing, and what does not
Test the soil first, since the pH decides the fix. Penn State Extension gives pin oak a range of pH 5.0 to 7.0, while soil over limestone in one Pennsylvania town runs as high as 7.4. On ground like that, chlorosis is chronic, and holding the soil in a pin oak’s range is a fight:
“Institutional landscape managers who have inherited pin oaks and white pine in this Pennsylvania community are forced to wage a yearly battle to maintain the soil pH within the desired range for these pH-sensitive specimens.” (Penn State Extension, Consider Soil pH Before Selecting Trees and Shrubs for Landscape Use)
Sulfur lowers the pH as a long-term fix, but it is hard to spread over the whole root zone of a grown tree, and many soils resist the change. Chelated iron or manganese is the stopgap. In the soil it needs repeating, sprayed on the leaves it lasts 60 to 90 days and greens only the leaves it touches, and a certified arborist’s trunk injection works for two or three years.
The lasting help is a better root zone. Take the grass out from under the crown, lay 3 to 4 inches of mulch, or 1 to 2 inches on clay, and water in dry spells.
Leave the fertilizer bag closed unless a soil test calls for it, since extra phosphorus and potassium can deepen chlorosis. Why the pH matters more than the bag is the subject of organic or synthetic fertilizer.
Trees that take limy ground
On limy ground, the lasting answer is a tree that takes it. These natives we grow do:
- Shumard oak is little troubled by the yellowing that alkaline soil causes in many oaks. Zones 5 to 9, 50 to 80 feet.
- Bur oak grows wild on limestone bluffs. Zones 3 to 8, 60 to 80 feet.
- Chinquapin oak does well in alkaline soil, at a pH of about 6.5 to 8, unlike most white oaks. Zones 3 to 8, 40 to 60 feet.
- Blue ash prefers thin, alkaline ground over limestone. Zones 4 to 7, 50 to 70 feet.
- Common hackberry grows fastest on neutral to limy loam. Zones 3 to 9, 40 to 60 feet.
- Eastern red cedar grows on thin, rocky ground over limestone. Zones 2 to 9, 30 to 50 feet.
Where to start
Read the leaves, then:
- A tree planted in the last two years: the new-tree check starts from yellow leaves and weighs water, soil and planting depth.
- An older tree yellow between green veins: a soil pH test before any treatment or fertilizer.
- Scattered yellow leaves in a dry spell: a deep soak over the roots, and nothing more.
- Still unsure: Blue Whale Trees answers questions about a tree you already have through its support page. Say when the yellowing began, and photos of the whole tree and a close-up of the leaves can follow by email once we reply.
Common questions
Why are my tree’s leaves turning yellow in July?
Scattered older leaves that yellow and drop in July and August are usually the normal summer shed, sped by dry weather. Yellow between green veins, or a whole limb turning at once, points instead to the soil pH, the roots or the trunk.
Why are my pin oak leaves turning yellow?
Most often iron chlorosis: on soil above pH 7 the iron is there, but the roots cannot take it up. Test the soil pH, since only a lower pH or a tree suited to the soil ends it.
Why are my river birch leaves turning yellow in summer?
River birch sheds yellowed leaves and twigs in late summer dry spells, so soak it deeply. If the leaves yellow between green veins, the soil is likely too alkaline, since river birch yellows from about pH 6.5.
Will fertilizer fix yellow leaves on a tree?
Not when the veins stay green, since the iron is already in the soil and extra phosphorus or potassium can make the yellowing worse. Chelated iron greens the leaves for a while, but the yellowing returns until the pH is corrected.
Sources
(6 references)
- Chlorosis: The Morton Arboretum, with its page River birch: the first pale green leaves and later yellowing, mild to advanced cases, scorched margins and early drop, one branch or the whole plant, iron and manganese unavailable above pH 7.0, iron in oaks and manganese in maples, excess phosphorus, potassium and magnesium, the species chlorotic on high-pH soil, saturated soil and roots without oxygen, drought yellowing without green veins, prevention by choosing the tree, chelated iron in the soil, foliar sprays lasting 60 to 90 days, trunk injections for two or three years, grass removed and 3 to 4 inches of mulch, water in dry periods, no potassium or phosphorus without a soil test, and river birch yellowing and dropping its leaves in severe drought.
- Fertilizing Trees and Shrubs and Nutrient Deficiency Symptoms: University of Maryland Extension: fertilizer as no remedy for landscape problems, the soil test, iron chlorosis as a yellowing between the veins of new leaves above pH 7.0, chelated iron as a temporary correction, sulfur to lower the pH, and poor drainage, overwatering, overmulching and deep planting as other causes of chlorosis.
- Chlorosis: University of Wisconsin-Madison Division of Extension, Wisconsin Horticulture, with Analyzing Reasons for Yellow Leaves (Bruce Spangenberg): pin oak the tree most often affected, the soil test before any treatment, sulfur to lower the pH and the difficulty of treating a grown tree’s root zone, mulch 1 to 2 inches deep on clay and 3 to 4 elsewhere and kept 4 inches from the trunk, older leaves shed for new growth, waterlogged soil and root injury, and weed killers among the causes of yellowing.
- Consider Soil pH Before Selecting Trees and Shrubs for Landscape Use: Penn State Extension: pin oak’s preferred pH of 5.0 to 7.0 against limestone soil near 7.4, decline and death on high-pH soil, the quotation, soil buffering that limits pH treatments, and hackberry and eastern red cedar for high-pH ground.
- Tulip poplar summer leaf drop: Purdue Landscape Report, Purdue University, with Flood Damage to Trees and Purdue Extension’s Transplant Shock of Trees and Shrubs (Paul C. Pecknold, BP-31): scattered yellow leaves dropping from late June through August under drought and root stress, the quotation, water as the remedy, a whole limb or crown as the sign of a root or trunk infection, borers or injury, saturated soil without oxygen, chlorosis and early leaf drop after flooding, growing-season flooding worse than winter flooding, decline after a little over two weeks under water, root rot afterward, yellowing among the signs of transplant shock, and the suffocated roots of a tree planted too deep.
- River Birch: Clemson Cooperative Extension, Home & Garden Information Center: river birch’s need for acid soil, chlorosis from pH 6.5, and leaves and twigs shed in late summer dry spells.
