Bee Plant of the Month: Horse Chestnut : 19 BEE PLANT OF THE MONTH Chestnut Horse E Bridget Beattie, PhD, NDB
veryone loves the horse chestnut tree; beekeepers and nature lovers for its candle- like flowers in April and school- children for its conkers in autumn. This is a tree for all seasons. Many insects
are nurtured from its nectar and pollen, especially bees of all persuasions, and honey bees may produce a surplus of horse chestnut honey. The leaves are food for caterpillars which, in turn, feed birds such as blue tits, while conkers are eaten by mammals, particularly our native deer as well as wild boar in mainland Europe. This stately ornamental tree with its broad, dense crown may grow up to 25 metres and live for 200–300 years. The compound, opposite leaves have five to seven pointed leaflets on a central stem which, when it falls, leaves a distinct scar resembling a horseshoe and its nails. The shiny, dark red, oval buds are sticky, giving the tree another of its common names, ‘sticky buds’, and are a source of propolis for honey bees.
Flowers
The tree produces hermaphrodite flowers (male and female parts together) as well as separate male and female ones. Male flowers produce pollen, as do the hermaphrodites, and the female and hermaphrodites both produce fruits. The mostly white flowers are held on upright cones of loose branching clusters called panicles, 20–30 cm in height, each having 10–30 individual flowers, 2 cm across. These are rather special because they have ‘nectar guides’ which are colour-coded. They have four or five petals with frilly edges and, as the flower develops, a yellow blotch on the lower petals changes colour through orange to pink. When a flower has been
April 2015 Vol 97 No 4
pollinated, the blotch turns red, a colour which bees do not see as their colour vision is shifted towards the ultraviolet end of the light spectrum. Thus bees are no longer attracted to the flower.
Fertilised flowers develop into spiky green fruits containing beautiful shiny red-brown seeds, or conkers, so beloved of children. Conkers are mildly poisonous although they are used in medicines for horses and extractions may be used to treat bruises.
Pollen Horse chestnut pollen is a distinctive brick-
red colour and is very noticeable on the bees’ hind legs when they bring it back to the hive. Individual grains are oval, 25 µm long and 21 µm across, with three long apertures, each with a pore (tricolpate) and conspicuous spines. As well as having such pretty flowers and handsome conkers, this tree has attractive dark grey-brown bark which flakes when the tree matures.
Statement in the Landscape
Consider growing the horse chestnut with an eye to the future for the wonderful statement it makes in the landscape. Unfortunately trees are often attacked by a leaf miner which turns the leaves brown but this happens late in the season and the trees do not appear to suffer set-back. The red horse chestnut, Aesculus carnea, flowers a little later than the common Aesculus hippocastanum but is also very beautiful and equally favoured by bees and other wildlife.
Cultivation The trees thrive in full sun and humus-rich,
moist soil which drains well. They can be purchased in pots from a nursery and these should be planted during spring or autumn in a hole three times the width of the pot and deep enough to take the root ball to ground level. Ensure the plant is upright and add a stake if necessary. Backfill the hole, tamp down lightly and water well. Mulching helps to retain moisture while the plant is getting established and it should be watered liberally in its early days, especially during dry weather. Growing from seed is fun as conkers germinate quickly and easily. Plant in a cold frame as soon as possible after collection, before the seeds dry out. In 6–12 months, the seedlings will be about 30 cm tall and may be moved to their permanent position. They respond well to Bonsai cultivation, for those with a penchant for miniaturisation.
Origins
The family includes trees and shrubs, mostly deciduous, characterised by palmate leaves, and members are to be found in many parts of the world. Our common horse chestnut is native to the Balkans of south-east Europe and after its introduction to the UK in the seventeenth century has become naturalised. The common name may be derived from its efficacy in curing horses of respiratory complaints, despite being mildly toxic, or perhaps from the scars left by fallen leaves. It is also sometimes called ‘buckeye’ although this name is used more for its family members in the Americas. ♠
Fact File: Horse chestnut
Aesculus hippocastanum Family: Hippocastanaceae
www.bee-craft.com
Bridget Beattie
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