American mountain ash

Photo: Bruce Marlin — CC BY-SA 2.5 · source

Survives zone 2 through 6

Harvest calendar

Best planted in early spring after your last frost, or in fall before the ground freezes, depending on your climate.

American mountain ash is a small, hardy boreal tree whose bright red berries are famous winter wildlife food for birds, bears and browsing moose and deer rather than a mainstream human food — the raw fruit is thin-fleshed, sour and heavily tannic, and only becomes reliably edible for people after the first hard freeze softens and sweetens it, when it can be used for pies and jelly. ⚠ Not just astringent: raw fruit in this group contains parasorbic acid, which causes vomiting, stomach cramps and diarrhoea if you eat any quantity of it. Cooking, freezing, drying or a hard frost converts it to harmless sorbic acid — which is exactly why every traditional recipe cooks it and why the fruit is picked after the first frosts.

Hardiness

Zone 2–6

Habit

Tree

Edible part

Fruit

Ripens

Summer–autumn

Mature size

Small tree 5–10 m, often multi-stemmed

Light

Full sun to partial

Soil pH

6.0–7.0 (near-neutral)

Environment

Boreal

Native range

Eastern North America — from Newfoundland and the Canadian Maritimes west to Ontario, Michigan, Wisconsin and Minnesota, and south through New England and the Appalachian Mountains to North Carolina and Tennessee. It reaches its largest size in cool, boreal-influenced sites on the northern shores of Lakes Huron and Superior.

Status

Wild

Years to fruit

2–4 yrs

Growth speed

Slow-growing — a small tree typically reaching around 10-12 m tall by 7 m spread at maturity.

Spacing

600 cm (236 in) apart — about 36 m² (388 sq ft) per plant

Leaf shape

Pinnately compound, rowan-type leaves with 13-17 lanceolate, sharply toothed leaflets each 5-8 cm long, turning clear yellow in autumn.

Root system

A branching 'heart root' — several primary roots divide from the root crown and angle both downward and outward, rather than forming one dominant taproot.

Fruit description

Berry-like pomes about 6-8 mm across, bright red, borne in dense clusters that ripen in early autumn and persist into winter. The flesh is thin and sour, rich in malic acid and tannin, making it quite astringent and unpalatable raw straight off the tree; after the first hard freeze the fruit softens and sweetens, at which point it can be eaten raw in moderation or cooked into pies, jelly, or dried and ground into a meal.

Propagation

By seed — collect ripe fruit in autumn and either sow immediately in a cold frame or store and give the seed 2 weeks warm followed by 14-16 weeks cold stratification before sowing as early in the year as possible; germination is often slow and uneven, and seedlings put on little top growth in their first year or two while they build a strong root system. Named ornamental selections are propagated by grafting.

Pollination

Self-fertile

The edible parts listed above are a starting point, not a field guide. Identify a plant with certainty — ideally against a local authority — before eating any part of it, and read the full disclaimer. Spotted something wrong? Report it.