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 from the olive family, built for ground that turns off other trees. It takes flooding, drought, wind, and even alkaline soil in stride, which is why it once lined so many streets and parking lots across North America. Its opposite, pinnately compound leaves and winged seeds, called samaras, set it apart from the lookalike mountain ash, a rose-family tree it isn't related to.
The tree earns its keep with shape and color. It runs 50 to 70 feet (15 to 21 m) tall with a broad, even crown, grows quickly when young, and turns a clean yellow in fall. Cold holds no fear for it, since it shrugs off winters down to -40°F (-40°C) and ranges across USDA zones 3 to 9.
There's a hard truth, though. The emerald ash borer, an invasive beetle, has killed hundreds of millions of ash and will reach almost any untreated tree in its path. 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 to build strong structure. An established ash asks for almost nothing, but it does need watching for borer.
Light
Plant ash in full sun for the densest crown and the best fall color, though it will take partial shade. The more direct light it gets, the stronger and more even the tree grows.
Water
Keep young trees in consistently moist, humusy loam while the roots take hold, watering roughly every 1 to 2 weeks in dry spells. Once established, ash handles occasional flooding and drought with ease and rarely needs your help.
Soil
Few trees are this easy about soil. Ash grows in clay, loam, or sand as long as it's reasonably well drained, and it tolerates a wide pH from 5.5 to 8.0, acidic through alkaline.
Temperature
This is a cold-hardy tree to the core, comfortable across roughly -40°F to 104°F (-40°C to 40°C) and at home in USDA zones 3 to 9. Winter is no threat to a healthy ash.
Humidity
Outdoor humidity is whatever it is, and ash doesn't mind. Air movement through the canopy matters more, since stagnant, damp air is what invites leaf fungus like anthracnose.
Feeding
An established landscape ash rarely needs feeding at all. Give a balanced complete fertilizer in spring only when a soil test points to a real deficiency, not on a calendar.
Pruning
Prune in late winter while the tree 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
Green ash matures at a substantial 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 the broad crown all the room it needs.
When to plant
Ash is planted as balled-and-burlapped or container stock in spring or fall, whenever the soil is workable. The small flowers open in April and May, before or just as the leaves push out, 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 looms over every other problem on this tree, so learn its signs first. Most of the rest are cosmetic and pass on their own. Match what you see below, then decide whether to act or simply watch.
Crown dying back from the top with D-shaped holes in the bark
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. Watch for tiny D-shaped exit holes, winding S-shaped galleries under loosened bark, and pale woodpecker flecking as the crown thins from the top down. A high-value tree with less than 30 to 50 percent canopy loss can be saved with professional systemic treatment, but a heavily infested one should come down fast, and you should never move ash firewood.
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
Slow decline with tufted witches-brooms and pale, undersized leaves
This is ash yellows, a phytoplasma infection that thins the tree over several years and throws up tufted witches-brooms of weak growth. There's no cure once it takes hold. Keep the tree watered and mulched to slow the slide, and take it down once declining limbs turn hazardous.
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 is ash anthracnose, a fungus that flares up in cool, damp springs and leaves irregular brown patches tracing the veins and margins. It mostly hits the lower, inner canopy and can drop leaves early, but a healthy tree shrugs it off and leafs out again. Rake up and destroy the fallen leaves, prune 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
These are ash flower galls, caused by a tiny eriophyid mite that distorts only the male flower clusters. They turn brown and hang on as dry clumps, but they never touch the leaves or the tree's health. No treatment is needed, though you can rake up fallen galls if the look bothers you.
Fix:
- No treatment is needed because the galls are cosmetic
- Rake and discard fallen galls if desired
Toxicity
Good news on this front. True ash is not on the ASPCA toxic-plant lists and is treated as safe for cats, dogs, and people alike, 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
True ash isn't on the ASPCA toxic list, so a curious cat batting at a fallen leaf has nothing to worry about. A big mouthful of any plant can still upset a sensitive stomach.
Dogs None
Ash is treated as non-toxic to dogs, and a chewed twig or leaf won't poison one. The bigger risk is a splinter from chewed wood, not the plant itself.
Horses None
Horses can graze around an ash without trouble, since the tree carries no known toxin for them.
Rabbits None
A rabbit that nibbles ash leaves or bark is safe. As with any new green, introduce it slowly so the gut adjusts.
Livestock None
Cattle, goats, and sheep can browse ash foliage without poisoning, and the leaves have long been cut as fodder in some regions.
Birds None
Backyard and wild birds come to no harm from ash. Many actually feed on the winged samaras through fall and winter.
People None
Ash poses no poisoning risk to people, and the wood has been worked and burned safely for generations. The tree isn't grown as food, so there's nothing here meant for the plate.
Keep ash firewood out of pet bedding only for splinter and mold reasons, not toxicity.
Varieties
Most ash sold for the yard are seedless male clones, chosen so they skip the litter of samaras and hold a reliable shape. These are the names you'll run into.
Patmore (green ash)
A seedless male green ash that takes the cold all the way to zone 2 and holds an even, tidy shape with clear yellow fall color.
Marshall's Seedless (green ash)
A long-popular seedless male green ash grown for its glossy, dark green summer foliage and freedom from messy seed.
Autumn Purple (white ash, Fraxinus americana)
A seedless male white ash clone planted for fall color that runs 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 and come from the grafting bench rather than a seed tray.
SeedModerate
Collect samaras in fall; sow after stratification for spring germination · 1 to 2 growing seasons to a transplantable seedling
Gather the winged samaras in fall and plan to wait, because the seed is dormant and won't sprout without a long chill. Give it cold, moist stratification near 35°F to 40°F (2°C to 4°C) for about 90 to 120 days, then sow for spring germination and let it grow on for one to two seasons before it's a transplantable seedling. The named seedless cultivars won't come true this way, so they're budded or grafted instead.
GraftingDemanding
Late summer budding or dormant-season grafting · 1 to 2 years to a saleable tree
This is the nursery's job, not an easy backyard project. 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 keeps them seedless and true to type. Give it one to two years to grow into a saleable tree.
Myths
Ash and mountain ash are the same tree.
They only share a name. True ash is Fraxinus, in the olive family, with opposite, pinnately compound leaves, while mountain ash is Sorbus, in the rose family, carrying 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.
When the dieback starts at the top and you find D-shaped exit holes and S-shaped galleries, you're looking at 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 an early systemic treatment by a professional gives a valued tree a chance.