Horse Chestnut

Quick facts

Full sun or part sun · medium water · well-drained soil · 50 ft apart (30 to 70) · direct sow or transplant

Fall transplanting is open for 13 more days. Next: fall, Sep 25 to Nov 15.

1. Transplant Aug 16 – Oct 4 Open now · 13 days left
   Also worksFall
   About 10 weeks before to 3 weeks before your first frost (Oct 25 here)
   Fall planting works in milder zones - the roots keep growing after the leaves drop. Water through the first dry spells of the following summer.
2. Direct sow Sep 25 – Nov 15 Opens in 4 days
   Worth a tryFall
   About 4 weeks before to 3 weeks after your first frost (Oct 25 here)
   Sow a fresh conker 2 inches deep where the tree will stand; it needs winter cold and cannot be dried out first. Protect from squirrels, and keep spare conkers out of reach of children and pets.
3. Transplant Mar 20 – May 22 Opens in 180 days
   Best timeSpring
   About 3 weeks before to 6 weeks after your last frost (Apr 10 here)
   Plant a container or balled-and-burlapped tree in early spring into deep, moist, well-drained soil in full sun. Measure first: it needs 35 feet of clear space in every direction.

Frost here: last around Apr 10 (Mar 27 to Apr 24 most years), first around Oct 25. Zone averages, your own yard may run a week or two either way.

One stage to settle in, then four that repeat each year. Windows are typical; your zone and weather move them.

1. In the garden, counted from transplant
2. 1

   Years 1-5 - young tree

   The first year after planting

   • ProtectMeasure the distance before you dig the hole
     This is the decision that cannot be undone. A horse chestnut reaches 60-80 feet tall and 50-70 feet wide, with heavy low branches and shallow spreading roots. Give it at least 35 feet of clear space in every direction - from the house, the drive, the sidewalk, the septic field and the property line. Almost every unhappy horse chestnut in a garden was planted too close to something, and the only remedy at that point is removal.
   • WaterWater deeply through the first three summersweekly
     Soak the root zone weekly in dry weather for the first three years, then taper off. Horse chestnut has no drought tolerance to speak of: a young tree that dries out browns at the leaf edges within days, and a mature one on a hot dry site scorches every August for the rest of its life. Choose a spot that stays evenly moist and it will need nothing.
   • MulchMulch wide, and keep it off the trunk
     Spread 3 inches of wood chips over as much of the root zone as you can manage, pulled back a hand's width from the bark. The roots run shallow and wide, and mulch does far more for them than watering does. Grass right up to the trunk competes hard and invites mower damage at the base.
   • PruneSet the branch structure in the first few years
     Horse chestnut naturally builds low, heavy limbs. While the tree is small, in late winter, remove crossing shoots and shorten anything that will become a low branch over a path or drive - it is a two-minute job now and a tree surgeon's invoice in twenty years. Never top the tree; it responds with weak, crowded regrowth.

   Watch for

   • Planted closer than 35 feet to a building, drive or paving
   • Leaf edges browning in the first dry spell
   • Mower and string-trimmer damage at the base of the trunk
3. 2

   The candles - spring bloom

   Apr to Jun, every year

   • InspectWatch the flowers change colour as the bees work them
     Each upright white panicle - a candle - carries dozens of flowers with a yellow blotch at the base of the petals. Once a flower has been visited and its nectar taken, that blotch turns pink then deep red, and bumblebees stop landing on it. You are watching a tree tell pollinators which flowers are still worth the trip. Bloom runs one to two weeks in May, earlier in the South.
   • ProtectDo not add flowers to anything edible
     Horse chestnut flowers are toxic like the rest of the tree. They are not an edible flower, not a tea, and not a garnish - keep fallen candles off food-preparation surfaces and out of children's play kitchens. There is no traditional culinary use of any part of this plant anywhere.

   Watch for

   • Late frost browning the opening candles (cosmetic; the tree recovers)
   • Bumblebees and honeybees working the flowers
   • Rusty-red weeping patches appearing on the trunk in spring (bleeding canker)
4. 3

   Full leaf, then the annual browning

   Apr to Aug, every year

   • InspectExpect brown leaves by August - and know which cause it is
     Almost every mature horse chestnut looks scorched by late summer, and it is nearly always cosmetic. Three causes look similar: leaf blotch (reddish-brown patches with a yellow halo, spreading from the leaflet edge in humid weather), simple drought scorch (crisp brown edges, worst in a dry August on a hot site), and Japanese beetle feeding in the eastern US (leaves skeletonized to lace between the veins). None of them kills the tree. See Threats for the differences.
   • WeedRake and remove the fallen leaves in autumn
     Leaf blotch overwinters in the fallen leaves and re-infects next year's canopy from the ground up. Raking them up and binning or hot-composting them is the only control that does anything on a large tree - spraying a 70-foot canopy is neither practical nor worth it. It also removes an enormous slippery leaf litter from paths.
   • WaterSoak it in a long drought, even when mature
     A mature horse chestnut on a lawn or a street verge in a dry summer sheds leaves early and looks half-dead by September. A few long, slow soakings through July and August - hours with a hose trickling, moved around the root zone - keep it in leaf. This matters more on shallow or compacted soil, and more in the South.

   Watch for

   • Reddish-brown blotches with yellow margins spreading in from leaflet edges (leaf blotch)
   • Pale wandering tunnels turning brown between the veins (leaf miner - Europe, not established in North America)
   • Lacy skeletonized leaves with beetles present (Japanese beetle)
   • Dark rusty ooze staining the trunk bark (bleeding canker)
5. 4

   Conker drop - the season that needs supervision

   Sep to Nov, every year

   • ProtectTeach the difference before the first conker falls
     Say it out loud to every child and dog owner who uses the space: this tree's nuts are POISON and are not the chestnuts you roast. Show them the husk - thick, leathery, with short widely spaced spikes you can flatten with a thumb - and the single round glossy seed inside. A sweet chestnut burr is a dense hedgehog of fine needles holding two or three flattened, pointed nuts. Handling conkers is completely safe. Eating one is not.
   • ProtectKeep dogs away from the drop zone
     Dogs are the animals that actually get poisoned by this tree, every autumn, and they do it by picking up fallen conkers on a walk. A conker causes vomiting, drooling, tremors and abdominal pain - and because it is big and hard, it can also lodge in the gut and need surgery. Leash dogs under the tree during the drop, and if one swallows a conker, call the vet immediately rather than waiting for symptoms.
   • DoRake up the conkers where people and animals go
     A mature tree drops thousands. Rake them weekly through the drop and bin them - not into compost that animals visit, and not into a hedge bottom where a dog will find them in November. Clearing them also removes a genuine slip hazard on paths and drives, and cuts down the crop of seedlings you would otherwise be pulling out of the borders next June.

   Watch for

   • Fallen conkers within reach of dogs, toddlers or livestock
   • Whole conkers piling up on paths and drives (slip hazard)
   • Split husks on the tree signalling the drop is starting
   • Seedlings germinating wherever conkers were left over winter
6. 5

   Winter - sticky buds and the pruning window

   Nov to Mar, every year

   • PrunePrune in late winter, and only what needs it
     Do structural pruning in the dormant season: dead, damaged, crossing or dangerously low limbs. Horse chestnut wood is not strong, and a heavy limb over a drive or a play area is worth removing before a storm removes it for you. Anything larger than a few inches across, or over a building, is a job for an arborist - not a ladder.
   • InspectCheck the trunk for bleeding cankers while the bark is bare
     Winter is the easiest time to see dark rusty or black weeping patches on the trunk and main limbs, the sign of bleeding canker. Note where they are and how big; a canker that stays the same size for years is common and survivable, while one girdling the trunk alongside dieback in the crown means the tree needs an arborist's judgement about whether it is still safe.
   • InspectThe sticky buds are the winter ID feature
     In winter horse chestnut is unmistakable: fat brown terminal buds up to an inch long, coated in a sticky varnish that waterproofs them, held in opposite pairs. Below each bud sits a horseshoe-shaped leaf scar with small dots arranged like nail holes - one of the two stories behind the tree's name.

   Watch for

   • Dark rusty ooze staining the bark (bleeding canker)
   • Dieback in the upper crown
   • Heavy low limbs over paths, drives or parking
   • Squirrels caching conkers into lawns and borders

Watch out for

5 to know. 1 is high-risk: Conker Poisoning (Aesculin & Saponins). 5 are active in September.

Good & bad neighbors

First rule: keep Sweet Chestnut apart. Do not plant these where their crops mix on the ground.

Varieties · 5

You pick one when you add Horse Chestnut to your garden. Its days to maturity set your harvest window.

• 'Baumannii' (Baumann's Horse Chestnut)

  Zones 3a to 7b

  Dense upright candles of fully double, pure white flowers in May on a large spreading tree; no fruit follows.

  sterileno-fruitdouble-floweredrecommended-for-gardens

  The form to plant if you want this tree in a place people use. 'Baumannii' carries fully double white flowers that last noticeably longer than the species', and it is completely STERILE - it sets no fruit at all. No conkers means no poisoning risk for children, dogs or livestock, no thousands of seeds to rake, no slip hazard on paths and drives, and no seedlings in the borders. It is the same 60-80 foot tree in every other respect, so the space rule still applies, and the leaves still brown in late summer. Grafted, so it cannot be raised from seed.

• Horse Chestnut (species, Aesculus hippocastanum)

  Zones 3a to 7b

  Broad, heavy-limbed tree with large palmate leaves, upright white flower candles, and thick leathery spiny husks holding one glossy brown conker.

  specieslarge-treetoxic-seedswhite-flowers

  The wild species and the standard park and avenue tree: 60-80 feet tall and nearly as wide, with palmately compound leaves of five to seven leaflets, upright white flower candles blotched yellow turning red in May, and heavy crops of thick-spiked husks each holding one large glossy poisonous seed. Superb where it has room; a long-running problem where it does not.

• Red Horsechestnut (Aesculus x carnea) - a DIFFERENT plant

  Rounded 30-40 foot tree with dark green palmate leaves and upright rose-red flower candles in late spring.

  related-specieshybridred-flowerssmaller-tree

  A different plant, listed for comparison: a hybrid of horse chestnut with the American red buckeye. It is much smaller - roughly 30-40 feet - with deep pink to red flower candles, better resistance to leaf blotch and scorch, and far fewer fruit. The seeds it does set are just as poisonous. Its size, spacing and disease behaviour all differ from this page's, so use a red horsechestnut guide rather than running one off the horse chestnut timeline. Often the better choice for a large garden that cannot take an 80-foot tree.

• 'Briotii' (Aesculus x carnea) - a DIFFERENT plant

  Compact rounded tree with glossy dark palmate leaves and vivid scarlet-red flower candles.

  related-specieshybridred-flowerssmaller-tree

  A selected form of the red horsechestnut hybrid above, not of horse chestnut itself, listed for comparison: deeper, brighter scarlet-red candles than the ordinary hybrid, a tidy rounded 30-40 foot habit, and very little fruit. Widely sold as a street and garden tree. Still toxic in all parts, and still a different plant from the tree this page describes.

• 'Fort McNair' (Aesculus x carnea) - a DIFFERENT plant

  Medium rounded tree with clean dark foliage and pink flower candles marked with yellow throats.

  related-specieshybridpink-flowersdisease-resistant

  Another selection of the red horsechestnut hybrid, listed for comparison: rich pink candles with yellow throats, notably good resistance to the leaf blotch and scorch that disfigure the species, and a manageable 30-40 foot size. A common recommendation where someone wants the horse chestnut look on a street or a suburban lot. All parts remain toxic.