Ash
Fraxinus americana
also called white ash, green ash, fraxinus
White ash and its tougher sibling green ash: fast, straight-grained shade trees with purple-bronze fall color, now planted only by gardeners willing to defend them.
- Type
- Tree · Perennial
- Botanical family
- Mixed / other
- Foliage color
- Green
- Sunlight
- Full sun
- Watering
- Moderate
- Soil
- Deep, moist, well-drained
- Feeding
- All-purpose balanced
- USDA zones
- 4a–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 and far-reaching
- Working depth
- 12–24 in
- Can reach
- 4 ft down where the soil allows
- Spread
- 98–148 ft across, about 2–3× the width of the plant
Almost all of a tree’s roots are in the top two feet of soil, where the air is, and they run out well past the branch tips. The deep taproot most people picture belongs to the seedling; the tree grows out of it and spends the rest of its life spreading sideways instead.
The habit is Ash’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. The calendar that matters is the emerald ash borer treatment cycle where the beetle is present.
- What to look for
- Crown thinning from the top, D-shaped exit holes in the bark, woodpeckers working the trunk hard in winter: all mean borer, and the time to act was already yesterday.
- How to harvest
- Structural pruning in the dormant season while young. Where the borer is established, a healthy ash worth keeping gets a systemic treatment through a certified arborist on a one-to-three-year cycle.
- How often
- A winter prune early on; treatment on its cycle for as long as you choose to defend the tree.
- Storing the crop
- Nothing to store. Do not move ash firewood — that is how the borer crosses counties.
- Emerald ash borer Emerald ash borer, the first question to ask before planting any ash at all
- Anthracnose Anthracnose spotting and dropping the spring leaves in a wet year
- Ash yellows Ash yellows stunting and brooming trees in the Northeast and Midwest
- Ash plant bugs stippling the leaves, cosmetic beside the borer
Beneficial predators that hunt this plant's pests — grow their favourite flowers nearby to recruit them. companion plant
- Garden birds PasseriformesHunts Emerald ash borer
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.
- Parasitic wasps Braconidae & TrichogrammaHunts Emerald ash borer
Tiny, stingless wasps that lay eggs in or on caterpillars, aphids, and moth eggs — the white cocoons riding a hornworm are their calling card, so leave that caterpillar be. Umbel flowers with shallow nectar keep the adults fuelled.
The wood of every baseball bat and axe handle. Be honest about the commitment before planting one: where emerald ash borer has arrived, an untreated ash is a dead ash within a few years.
The Cottage Garden Companion — the gardener's herbarium at cottagegardencompanion.com