American elm
Ulmus americana
also called white elm
The vase-shaped street tree that once arched over every main street in America, coming back now through cultivars bred to stand against the disease that took it.
- Type
- Tree · Perennial
- Botanical family
- Mixed / other
- Foliage color
- Green
- Sunlight
- Full sun
- Watering
- Moderate
- Soil
- Adaptable; best in deep, moist, fertile ground
- Feeding
- All-purpose balanced
- USDA zones
- 3a–9a
- Frost tolerant
- Yes
- Plant out
- 14 days before the last spring frost
- Plant spacing
- 39 ft 4 in
- In-row spacing
- 32 ft 10 in
- Between rows
- 49 ft 3 in
- Square-foot density
- Not suited to SFG
- Root system
- Woody, shallow, wide and opportunistic
- Working depth
- 12–24 in
- Can reach
- 3.5 ft down where the soil allows
- Spread
- 177–236 ft across, about 3–4× the width of the plant
These roots go looking, and what they find is drains, soakaways, footings, paving and the border next door. Give it real distance from anything you would mind being lifted or blocked: the reach below ground is several times what the crown suggests.
Shallow, wide and thirsty, and long known for finding drains and lifting sidewalks. Where a street elm survived the disease, the pavement around it usually did not.
The habit is American elm’s own; the figures are what that habit usually comes to at this size, not a measurement of this species. Roots follow the soil either way: a compacted pan, a high water table or heavy clay stops them well short of any of it, and deep open ground lets them go further.
- When
- Not harvested. Prune only in late fall and winter, and treat that rule as law.
- What to look for
- Deadwood, rubbing limbs, or the classic vase getting congested in the middle.
- How to harvest
- Clean cuts in the dormant season, when the bark beetles that carry Dutch elm disease are not flying. Never prune an elm between April and October, and get any suddenly wilting, yellowing limb ("flagging") removed and burned at once.
- How often
- A dormant-season check each year while young; every few years once grown.
- Storing the crop
- Nothing to store. Never stack fresh elm firewood near a living elm — beetle brood matures in it.
- Bark beetles Elm bark beetles breeding under the bark of dying limbs and carrying the fungus tree to tree
- Japanese beetle Japanese beetles and other chewers on the leaves, seldom serious on a big tree
- Leafhoppers Leafhoppers spreading elm yellows in the Midwest
- Dutch elm disease Dutch elm disease, the whole reason to insist on a resistant cultivar
Beneficial predators that hunt this plant's pests — grow their favourite flowers nearby to recruit them. companion plant
- Assassin bug Reduviidae
A patient ambusher with a curved beak it drives into whatever it catches — caterpillars, beetles, bugs, and the occasional bee, so count it a generalist rather than a specialist. It will jab a careless finger too, so admire it and leave it be.
- Garden birds Passeriformes
Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray.
- Beneficial nematodes Steinernema & Heterorhabditis spp.Hunts Japanese beetle
Microscopic worms watered onto damp soil that hunt down soil-dwelling grubs and release a bacterium that kills them within days. Timing is the whole thing: warm, damp soil and a small target grub, which means late summer for most of what they are used against.
- Big-eyed bug Geocoris spp.Hunts Leafhoppers
A stubby 3 mm bug with enormous wrap-around eyes, working the soil surface and the low foliage for aphids, mites, thrips and insect eggs. It is the main natural check on chinch bugs in a lawn and it is killed outright by insecticide.
- Damsel bug NabidaeHunts Leafhoppers
A slender, mantis-armed bug that grabs aphids, small caterpillars, and thrips in low crops and meadowy edges. Leave a strip of unmown grasses and flowers for it to overwinter in.
- Praying mantis MantidaeHunts Japanese beetle
A sit-and-wait ambusher that snatches caterpillars, beetles, and anything else that wanders close — friend and foe alike, so count it a mixed blessing. Tall, structured plantings give it perches and egg-case anchors.
- Spiders AraneaeHunts Leafhoppers
Webs, ambushes, and night patrols make spiders the garden’s steadiest generalist predators, taking whatever flies or crawls past. Mulch, ground cover, and undisturbed corners keep the population dense.
- Spined soldier bug Podisus maculiventrisHunts Japanese beetle
A predatory stink bug — same shield outline as the pest, but with a sharp spine at each shoulder and a beak it uses to spear caterpillars and beetle grubs. Learn the spines before you squash a shield bug, because this one is on your side.
- Tachinid fly TachinidaeHunts Japanese beetle
Bristly, house-fly-lookalike parasitoids that lay eggs on caterpillars, beetle grubs, and earwigs — the maggot consumes the host from within. Adults sip nectar from shallow umbels and daisies.
Plant a named resistant cultivar ('Princeton', 'Valley Forge', 'New Harmony'), never a seedling: the species itself still dies young of Dutch elm disease almost everywhere.
The Cottage Garden Companion — the gardener's herbarium at cottagegardencompanion.com