Aesculus hippocastanum, horse chestnut
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Broadleaf Deciduous Trees

Aesculus hippocastanum

horse chestnut

Sapindaceae

Balkan Peninsula — northern Greece, Albania, Bulgaria, North Macedonia

At a Glance

TypeTree
HabitSpreading
FoliageDeciduous
Height50-75 feet (15-23 m)
Width40-60 feet (12-18 m)
Maturity25 years

Growing Zones

USDA Hardiness Zones

4 - 8
Zone 4
Zone 5
Zone 6
Zone 7
Zone 8
These zones indicate the coldest temperatures this plant can typically survive.
Frost Tolerancehardy

Key Features

Attracts Pollinators
Deer Resistant
Maintenancelow

Overview

Aesculus hippocastanum is a large deciduous tree reaching 50–75 feet (15–23 m) tall and 40–60 feet (12–18 m) wide, with a broad, rounded crown. Leaves are palmately compound with 5–7 leaflets, each 4–10 inches (10–25 cm) long, dark green above with a coarse, wrinkled texture. In May through June, upright panicles of white flowers 8–12 inches (20–30 cm) tall rise above the foliage; individual flowers are 0.75 inch (2 cm) across with yellow blotches that turn red after pollination. Fruit are round, spiny green capsules 1.5–2.5 inches (4–6 cm) across, ripening September through October and releasing 1–3 glossy brown seeds (conkers). Bark is dark gray-brown, developing plated scales with age. Notably large, sticky resinous buds are a reliable winter identification feature. Growth rate is moderate, 1–2 feet (30–60 cm) per year. All parts of the plant are toxic to humans and animals if ingested; conkers contain aescin and should be kept away from children and pets. In humid Pacific Northwest conditions, the fungal leaf blotch disease Guignardia aesculi reliably disfigures foliage by July through August — leaves develop brown scorched patches and the tree appears in poor health by late summer. This is cosmetic rather than fatal, but it is a consistent performance limitation in wet coastal climates. The hybrid Aesculus × carnea 'Briotii' shows significantly better resistance and may be preferable for PNW plantings.

Native Range

Native to a small area of the Balkan Peninsula — the Pindus Mountains of northern Greece and Albania, and scattered populations in Bulgaria and North Macedonia. Found in mixed montane forests at elevations from 2,600 to 4,900 feet (800–1,500 m). Widely introduced across Europe and North America.

Suggested Uses

Planted as a large specimen shade tree in parks, estates, and spacious public landscapes. Requires a minimum of 40 feet (12 m) horizontal clearance from structures. In PNW coastal gardens, the consistent late-summer leaf blotch reduces aesthetic value — Aesculus × carnea 'Briotii' is a more reliably attractive alternative in humid conditions. Not suitable for planting near playgrounds, pet areas, or locations where conkers are accessible to children or animals.

How to Identify

Identified by large palmately compound leaves with 5–7 leaflets and upright white flower panicles 8–12 inches (20–30 cm) tall in May through June. Fruit are round, distinctly spiny green capsules containing 1–3 glossy brown conkers — spiny capsules distinguish it from Aesculus × carnea, which has smooth or lightly warty capsules. Large, very sticky dark brown resinous buds are a reliable winter identification feature. Crushed leaflets have a faint unpleasant odor.

Appearance

Size & Dimensions

Height50' - 75'
Width/Spread40' - 60'

Reaches mature size in approximately 25 years

Colors

Flower Colors

white
yellow
red

Foliage Colors

dark green

Fall Foliage Colors

yellow
brown

Bloom Information

Bloom Period

~4 weeks
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Spring
Blooms May through June, with upright panicles of white flowers 8–12 inches (20–30 cm) tall above the expanded foliage. Individual flowers are 0.75 inch (2 cm) across, white with yellow blotches that turn red after pollination — a visual signal to pollinators that nectar has been depleted. Panicles last 3–4 weeks. Spiny fruit capsules ripen September through October.

Detailed Descriptions

Flower Description

white with yellow and red markings

Foliage Description

dark green in summer, often disfigured by leaf blotch by late summer; yellow-brown in fall

Growing Conditions

Sun Requirements

Full Sun
Partial Shade
Requires 4-8 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 7.5(Neutral)
357912
Soil Types
loamclaysilt
Drainage
well drained

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Time to Maturity

20-30 years

Care & Maintenance

Care Guide

Establish with regular deep watering for the first 2–3 growing seasons; once established, the tree tolerates average moisture conditions. Apply 3–4 inches (8–10 cm) of mulch from the drip line inward, keeping 6 inches (15 cm) clear of the trunk. Guignardia leaf blotch develops reliably in wet coastal PNW conditions: brown scorched patches appear on leaves from July onward, and the tree looks poor by late summer — this does not kill the tree but is a predictable limitation. Fallen leaves and spiny capsules should be raked up in autumn; conkers are a slip hazard on hard surfaces and are toxic to humans and animals if ingested. Allow 40–60 feet (12–18 m) horizontal clearance; surface roots can be aggressive in compacted soils.

Pruning

Prune during full dormancy (November through February). Remove dead, damaged, or crossing branches. The tree develops a strong natural structure with minimal corrective pruning; heavy pruning creates large wounds that heal slowly and introduce decay. Structural pruning of young trees in years 5–15 to develop a clear trunk and well-spaced scaffold branches is beneficial. Avoid removing large limbs from mature trees. Do not prune in spring during active growth.

Pruning Schedule

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Maintenance Level

low

⚠️ Toxicity Warning

Toxic to pets and humans