Tree · Oleaceae
Green Ash
Fraxinus pennsylvanica
A tough, fast shade tree for hard sites, now living under the shadow of the emerald ash borer.
Full sun
Every 7–14 days
USDA 3–9
50–70 ft · 15.2–21.3 m
Overview
Green ash is a fast-growing native shade tree in the olive family, and it thrives on ground where other trees fail, which makes it a generous anchor for a difficult property. Flooding, drought, wind, and alkaline soil scarcely register, and that resilience is why it once lined streets and parking lots across North America. Its opposite, pinnately compound leaves and winged seeds, called samaras, are what set it apart from the lookalike mountain ash, a rose-family tree it is not related to.
Across a yard it brings real presence, rising 50 to 70 feet (15 to 21 m) tall under a broad, even crown, filling out fast in its early years and turning a clean yellow each autumn. Cold poses no threat, since it endures winters down to -40°F (-40°C) and settles comfortably across USDA zones 3 to 9.
One honest caveat shapes how this tree fits a landscape today. The emerald ash borer, an invasive beetle, has killed hundreds of millions of ash and reaches almost any untreated tree in time. Most extension services no longer recommend planting new green ash, so the considered approach is to care for the trees already standing and watch them closely.
Care
The short version: give it full sun and room to spread, keep young trees evenly moist, and prune in late winter for a strong frame. An established ash asks almost nothing of a property, though it earns a watchful eye for borer.
Light
Give ash full sun for the densest crown and the best fall color, though it will accept partial shade where that is what a site offers. The more direct light it draws, the stronger and more even the tree grows.
Water
Keep young trees in consistently moist, humusy loam while their roots establish, watering roughly every 1 to 2 weeks through dry spells. Once settled, ash takes occasional flooding and drought in stride and rarely needs any help.
Soil
This is an unusually adaptable tree underfoot. Ash grows in clay, loam, or sand so long as it drains reasonably well, and it tolerates a wide pH from 5.5 to 8.0, acidic right through to alkaline.
Temperature
This tree is deeply cold-hardy, at ease anywhere from about -40°F to 104°F (-40°C to 40°C) and right at home across USDA zones 3 to 9. Winter is no threat to a healthy ash.
Humidity
Whatever the outdoor humidity, ash takes it as it comes, so there is nothing to manage there. Air movement through the canopy matters more, since stagnant, damp air invites leaf fungus such as anthracnose to settle in.
Feeding
An established landscape ash rarely needs feeding. Offer a balanced complete fertilizer in spring only when a soil test shows a genuine deficiency, never on a calendar.
Pruning
Prune in late winter while the tree is dormant, clearing dead, broken, or crossing limbs and shaping a strong structure early. The wood is brittle and prone to wind and ice breakage, so the good form you build now pays off for decades.
Repotting
none
Size & spacing
Green ash matures at 50 to 70 feet (15 to 21 m) tall and spreads 35 to 50 feet (11 to 15 m) wide. Site it well clear of buildings, walks, and power lines, and give that broad crown all the room it needs.
When to plant
Plant ash as balled-and-burlapped or container stock in spring or fall, whenever the soil is workable, which leaves a wide window to fit it into a planting season. The small flowers open in April and May, just before or as the leaves emerge, and the winged seeds ripen through fall.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring or fall; balled-and-burlapped or container stock when soil is workable
- Harvest: Inconspicuous flowers April to May before or as foliage emerges; samaras mature in fall
Hardiness
USDA hardiness zones: 3–9
Temperature: down to -40°C
Troubleshooting
One pest outweighs every other concern on this tree, so it is the first thing to learn to read. The rest are mostly cosmetic and tend to resolve on their own. Match what you are seeing to the picture below, then decide whether to act or simply keep watch.
The upper canopy thinning out while small D-shaped holes appear across the bark
Catching this one early changes everything about how a property fares. The cause is the emerald ash borer, an invasive beetle whose larvae quietly girdle the trunk from inside the bark, and it takes down nearly every ash left untreated. Watch for those small D-shaped exit holes, the looping S-shaped galleries tucked beneath bark that has gone loose, the pale flecking where woodpeckers have been working, and a crown that fades from the top toward the ground. A treasured specimen still showing less than 30 to 50 percent canopy loss has a real shot, since professional systemic treatment can carry it through; a tree already badly hit is best brought down without delay, and never move ash firewood, since that is how the beetle spreads from place to place.
Fix:
- Confirm infestation and assess canopy loss
- Treat high-value trees with under 30-50 percent canopy loss using a systemic insecticide on a professional schedule
- Remove and properly dispose of heavily infested or dead trees promptly because untreated ash usually die
- Do not move ash firewood, which spreads the beetle
A slow fade marked by tufted witches-brooms and small, pale foliage
This is ash yellows, a phytoplasma infection that thins the tree over several years and pushes up tufted witches-brooms of weak, crowded twigs. There is no cure once it takes hold, though you can still ease the path. Steady watering and a good mulch ring slow the decline and buy a few more seasons, and when failing limbs begin to threaten what is below, that is the time to schedule removal.
Fix:
- No effective cure exists
- Maintain vigor with proper watering and mulch
- Remove severely declining trees that become hazardous
Brown markings following the leaf veins once the spring weather turns damp
This problem reads as worse than it is and asks little of you. It is ash anthracnose, a fungus that stirs in cool, soaked springs and leaves uneven brown marks along the veins and edges. It tends to settle in the lower, inner part of the canopy and can shed leaves ahead of schedule, yet a healthy tree shrugs it off and flushes new growth without help. Sweep up and discard the dropped leaves, open the structure a little for better airflow, and skip the fungicide on an established tree in the landscape.
Fix:
- Rake and destroy fallen infected leaves to reduce overwintering inoculum
- Prune to improve air circulation
- Maintain tree vigor with proper watering; fungicides are rarely warranted on established trees
Clumpy green-then-brown galls gathered on the spring blooms
Here is one to leave well alone. These are ash flower galls, the doing of a tiny eriophyid mite that warps only the male flower clusters into odd little knots. They darken to brown and hang on as dry clumps, but they never touch the leaves or the wider health of the tree, so nothing needs fixing. No treatment is called for, and if the look ever bothers you, raking up the fallen galls is entirely a matter of taste.
Fix:
- No treatment is needed because the galls are cosmetic
- Rake and discard fallen galls if desired
Toxicity
Reassuring news for any household: true ash does not appear on the ASPCA toxic-plant lists and is considered safe for cats, dogs, and people, with no known poisoning risk to grazing animals or birds. The point to keep clear is that it is not the unrelated mountain ash or prickly ash, which are entirely different plants.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
You can set this worry aside: true ash is absent from the ASPCA toxic list, so a curious cat batting at a fallen leaf is perfectly fine. A really large mouthful of any plant can still unsettle a sensitive stomach, as ever.
Dogs None
For dogs, ash registers as non-toxic, and a chewed twig or leaf will not poison them. The greater concern is a splinter from gnawed wood rather than the plant itself.
Horses None
Horses can graze around an ash with no trouble at all, since the tree carries no toxin known to bother them.
Rabbits None
A rabbit nibbling ash leaves or bark stays safe. Just bring any new green in gradually so the gut has time to adjust.
Livestock None
Cattle, goats, and sheep can browse ash foliage without any risk of poisoning, and in some regions the leaves have long been cut as fodder.
Birds None
Backyard and wild birds are unharmed by ash. Many of them feed happily on the winged samaras straight through fall and into winter.
People None
There is no poisoning risk to people, and the wood has been worked and burned safely for generations. It is simply not grown as food, so nothing here is meant for the plate.
Keep ash firewood out of pet bedding only for splinter and mold reasons, not toxicity.
Varieties
Most ash chosen for the yard are seedless male clones, picked to skip the litter of samaras and to hold a reliable shape season after season. Here are the names you will come across.
Patmore (green ash)
A seedless male green ash that takes cold in stride, hardy all the way to zone 2, holding an even, tidy shape with clear yellow color in fall.
Marshall's Seedless (green ash)
A longtime favorite, this seedless male green ash is prized for its glossy, dark green summer foliage and for leaving no messy seed behind.
Autumn Purple (white ash, Fraxinus americana)
A seedless male white ash clone grown for fall color that moves from reddish purple to deep mahogany and lingers on the tree.
How to propagate
Ash grows readily from seed if you have the patience for its long chill, but the prized cultivars are a different matter, coming from grafting rather than from a seed tray.
SeedModerate
Collect samaras in fall; sow after stratification for spring germination · 1 to 2 growing seasons to a transplantable seedling
Ash grows readily from seed if you have the patience for its long chill, since the seed is dormant and will not sprout without one. Gather the winged samaras in fall, then provide cold, moist stratification near 35°F to 40°F (2°C to 4°C) for about 90 to 120 days, and sow afterward for spring germination, growing the seedling on for one to two seasons before it is ready to move. Bear in mind that the named seedless cultivars will not come true this way, so those are budded or grafted instead.
GraftingDemanding
Late summer budding or dormant-season grafting · 1 to 2 years to a saleable tree
This belongs to the nursery rather than the backyard, so there is no need to take it on yourself. Named clones such as Patmore, Marshall's Seedless, and Autumn Purple are budded in late summer or grafted during the dormant season onto seedling rootstock, which is what keeps them seedless and true to type. Allow one to two years for the graft to grow into a saleable tree.
Myths
Ash and mountain ash are simply two names for one tree.
They share a name and little else. True ash is Fraxinus, part of the olive family, carrying opposite, pinnately compound leaves, while mountain ash is Sorbus, a rose-family tree with alternate leaves and clusters of red berries. Sitting in entirely separate genera, the care advice for one will rarely fit the other.
A thinning ash crown just wants a little water and feeding to perk back up.
This is the one worth spotting early. When dieback starts right at the top and you find D-shaped exit holes along with S-shaped galleries, the cause is emerald ash borer, not thirst or hunger. No watering or feeding will halt it, and untreated trees usually die within about 2 to 5 years. Only early professional systemic treatment gives a valued tree a real chance.