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 does well right where other trees fail, which makes it pretty forgiving. Flooding, drought, wind, alkaline soil? None of it bothers it much, so it once lined streets and parking lots all across North America. The 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.
It grows 50 to 70 feet (15 to 21 m) tall with a broad, even crown, moves fast when young, and gives you clean yellow fall color. Cold? Not a problem, since it is hardy to -40°F (-40°C) and happy across USDA zones 3 to 9.
There is one honest catch worth knowing. The emerald ash borer, an invasive beetle, has killed hundreds of millions of ash and reaches almost any untreated tree eventually. Most extension services no longer recommend planting new green ash, so the smart move 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 strong structure. An established ash needs almost nothing from you, but do watch for borer.
Light
Plant ash in full sun for the densest crown and the best fall color, though it will tolerate partial shade if that is what you've got. The more direct light it gets, the stronger and more even the tree turns out.
Water
Keep young trees in consistently moist, humusy loam while the roots establish, watering roughly every 1 to 2 weeks in dry spells. Once it is established, ash tolerates the occasional flooding and drought and rarely needs your help.
Soil
This tree is really adaptable about where it sits. Ash grows in clay, loam, or sand as long as it is reasonably well drained, and it tolerates a wide pH from 5.5 to 8.0, acidic right through to alkaline.
Temperature
Ash is very cold-hardy and comfortable anywhere from about -40°F to 104°F (-40°C to 40°C), which is USDA zones 3 to 9. Winter is no threat to a healthy ash.
Humidity
Outdoor ambient humidity doesn't really matter to ash, so there is nothing to worry about there. What matters more is air movement through the canopy, because stagnant, damp air invites leaf fungus like anthracnose.
Feeding
An established landscape ash rarely needs feeding. Give it a balanced complete fertilizer in spring only when a soil test shows a real deficiency, not just because the calendar says so.
Pruning
Prune in late winter while it is dormant, taking out dead, broken, or crossing limbs and shaping strong structure early. The wood is brittle and prone to wind and ice breakage, so good form pays off for decades.
Repotting
none
Size & spacing
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 room to grow.
When to plant
Plant ash as balled-and-burlapped or container stock in spring or fall, whenever the soil is workable, so you've got a nice wide window. The small flowers open in April and May, right before or as the leaves emerge, and the winged seeds ripen through the 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 all the other problems on this tree, so its signs are the first thing to learn. The rest are mostly cosmetic and tend to sort themselves out. Match what you are seeing to the entry below, then decide whether to act or just keep watch.
The crown is dying back from the top down, with little D-shaped holes in the bark
So here is the big one, and catching it early really does count. This is the emerald ash borer, an invasive beetle whose larvae girdle the tree from inside the bark, and it kills nearly every untreated ash it gets to. What gives it away? Tiny D-shaped exit holes, winding S-shaped galleries tucked under bark that has gone loose, pale flecking where woodpeckers have been at work, and a crown that thins from the top down. A high-value tree losing less than 30 to 50 percent of its canopy can still be saved with professional systemic treatment, but a heavily infested one should come down fast. And whatever you do, never move ash firewood, because that is how the beetle spreads.
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 decline, with tufted witches-brooms and pale, undersized leaves
This is ash yellows, a phytoplasma infection that thins the tree out over several years and throws up tufted witches-brooms of weak growth. Once it has taken hold there is no cure, sadly, but you can still do something. Watering and mulching helps slow it down, and when the declining limbs start to turn hazardous overhead, that is when you have the tree removed.
Fix:
- No effective cure exists
- Maintain vigor with proper watering and mulch
- Remove severely declining trees that become hazardous
Brown blotches along the leaf veins after a wet spring
This one looks worse than it is, so you can ease up. It is ash anthracnose, a fungus that flares up in cool, damp springs and leaves irregular brown patches tracing the veins and edges of the leaves. It mostly hits the lower, inner part of the canopy and can drop leaves early, but a healthy tree shrugs it off and re-leafs just fine. Rake up and toss the fallen leaves, prune a bit for better airflow, and skip the fungicide on an established tree.
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-to-brown galls on the spring flowers
Here is one you can just leave alone. These are ash flower galls, caused by a tiny eriophyid mite that distorts only the male flower clusters. They turn brown and hang around as dry clumps, but they never affect the leaves or the tree's health, so there is nothing to do. No treatment is needed, and if the look bugs you, raking up the fallen galls is entirely up to you.
Fix:
- No treatment is needed because the galls are cosmetic
- Rake and discard fallen galls if desired
Toxicity
Some good news here. True ash is not on the ASPCA toxic-plant lists and is safe for cats, dogs, and people, with no known poisoning risk to grazing animals or birds. Just don't confuse it with the unrelated mountain ash or prickly ash, which are different plants entirely.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
You can relax here: true ash is not on the ASPCA toxic list, so a curious cat batting around a fallen leaf is totally fine. That said, a big mouthful of any plant can still upset a sensitive stomach.
Dogs None
Ash is non-toxic to dogs, and a chewed twig or leaf won't poison your dog. The bigger risk is a splinter from the chewed wood, not the plant.
Horses None
Horses graze around ash with no trouble at all, since there is no toxin known to bother them.
Rabbits None
A rabbit nibbling on ash leaves or bark is perfectly safe. Just introduce any new green slowly so the gut has time to adjust.
Livestock None
Cattle, goats, and sheep can browse ash foliage without any 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 actually feed on the winged samaras right through fall and winter.
People None
There is no poisoning risk to people, and the wood has been worked and burned safely for generations. It just isn't grown as a food, so there is nothing here for the plate.
Keep ash firewood out of pet bedding only for splinter and mold reasons, not toxicity.
Varieties
Most ash grown for the yard are seedless male clones, chosen so you skip the samara litter and get a reliable shape. Here are the names you'll run into.
Patmore (green ash)
A seedless male green ash that is cold-hardy clear to zone 2, with an even, tidy shape and clear yellow fall color.
Marshall's Seedless (green ash)
A long-popular seedless male green ash, prized for its glossy, dark green summer foliage and the bonus of no messy seed.
Autumn Purple (white ash, Fraxinus americana)
A seedless male white ash clone whose fall color runs reddish purple to deep mahogany and lingers on the tree.
How to propagate
Ash grows readily from seed if you've got patience for the long chill, but the prized cultivars are a different story and come from grafting, not seed.
SeedModerate
Collect samaras in fall; sow after stratification for spring germination · 1 to 2 growing seasons to a transplantable seedling
Ash grows from seed readily enough if you have the patience for the long chill, since the seed is dormant and just won't sprout without it. Gather the winged samaras in fall, then give them cold, moist stratification near 35°F to 40°F (2°C to 4°C) for about 90 to 120 days, and sow after that for spring germination, growing the seedling on for one to two seasons until it is ready to transplant. The named seedless cultivars won't 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 is a nursery job, not an easy backyard project, so don't feel you need to take it on. Named clones like Patmore, Marshall's Seedless, and Autumn Purple are budded in late summer or grafted in the dormant season onto seedling rootstock, which is what keeps them seedless and true to type. Give it one to two years for the graft to grow into a saleable tree.
Myths
Ash and mountain ash are the same tree.
They only share a name, really. True ash is Fraxinus, in the olive family, with opposite, pinnately compound leaves, while mountain ash is Sorbus, a rose-family tree with alternate leaves and clusters of red berries. They are unrelated genera, so advice for one rarely fits the other.
An ash with a thinning crown just needs water and fertilizer to bounce back.
Worth catching early, this one. Dieback that starts at the top plus D-shaped exit holes plus S-shaped galleries adds up to emerald ash borer, not thirst or hunger. No amount of watering or feeding stops it, and untreated trees usually die within about 2 to 5 years. Only early professional systemic treatment gives a valued tree a chance.