Horse chestnut

Value to bees

Nectar

Very high

Pollen

Very high

As a honey crop

Minor honey crop — a surplus only locally or occasionally

Which bees, and why

Worked heavily by honey bees and bumblebees. The colour-change mechanism is one of the clearest demonstrations of bee learning available to an ordinary observer — watch a panicle for a few minutes and you will see bees skipping the red-marked flowers.

Nectar sits fairly deep in the flower, which favours bumblebees and honey bees over very short-tongued species.

Worth knowing

Top-rated for both, in enormous quantity, from a single tree. One mature horse chestnut is worth a considerable area of border planting.

Flowering

In flower

April to May (northern hemisphere)

Two to three weeks in late spring, and a very large quantity of forage in that window because of the sheer size of the tree.

When nectar flows

Copious nectar and abundant pollen. The nectar guide at the base of each petal starts yellow and turns red once the flower has been pollinated and stops producing nectar — bees learn the signal quickly and stop visiting the red ones, which saves the tree and the bee time.

Year-to-year variation

Reliable in flower. A surplus is uncommon because the flow arrives during rapid colony expansion.

What it does to the honey

Where a surplus occurs, horse chestnut honey is amber, slightly bitter and quick to set. It is rarely sold on its own and usually goes into spring multiflorals.

Growing it

Conditions

Sun, deep moist soil. Too large for most gardens and a classic parkland and avenue tree.

Size

20-35 m.

Native range

The Balkan peninsula — a surprisingly small native range for so widely planted a tree, and it is threatened in the wild.

Suits

Large gardens, Orchard

• Far too big for a small garden — this is a parkland tree, and planting one in a suburban plot is a decision the next owner will have to live with.
• Horse chestnut leaf miner has defoliated trees across Europe since the 1980s. It is disfiguring and rarely fatal, and does not affect the flowering.
• Not the source of edible chestnuts. Conkers are toxic; sweet chestnut is a different tree in a different family.

What it looks like

A large spreading tree with distinctive palmate leaves of five to seven leaflets, and upright candelabra panicles of white flowers with a yellow blotch at the base of each petal, turning red with age.