The Honey Locust Tree

The Honey Locust Tree - Its growth requirements, life cycle, fruit pods and the uses they can be put to including ethanol.

The honey locust is a North American tree. It was occasionally naturalised in Central and Southern Europe. Other common names used for it include Sweet bean, Sweet locust and Honeyshuck.

In warm climates the honey locust can grow into a large tree up to 45 meters tall, but more commonly it grows to 21m (75ft) with a spread of 16m (55ft). Trees are deep rooted, long lived and open growing with a long trunk. Trees frequently send up suckers from the roots.

The trunk and branches are usually densely armed with stout, sharp, flat thorns, although several thornless forms exist and these are usually in ornamental plantings. Below most leaves and buds it bears 3 spines, the central one larger than the other two

The leaves emerge in late spring, usually missing any late frosts, and fall early in the autumn. The small leaflets decompose quickly. They turn a clear bright yellow in the autumn before falling.

The trees are mainly dioecious (i.e. with male and female flowers mainly on separate trees), although most trees actually bear some of both sexes of flowers. Flowering begins early at about 5-10 years. The sex of the tree cannot be identified other than by the flowers.

Fruit forms on the female trees, and do not require male trees to produce this although they are required for full seed production. The pods contain up to 20 seeds embedded in a brown sugary pulp. The seeds are 21-36% of the weight of the pods. Honey locust trees are biennial in nature, bearing heavy crops every other year. The pods drop gradually after ripening from October to late winter. The pods make excellent fodder.

The pulp around the seeds in the pods is edible, being sweet and molasses-like, and sugar can be extracted from it. Pods generally contain 12-14% sugar, although in selected cultivators this rises to up to 40%. Various North Americans recipes exist for making beer from the pulp.

The tender young pods are edible when cooked. Also edible are the seeds, raw or cooked; the young seeds taste like raw peas. The seeds are sweet, containing up to 30% sugar, also 10-22% protein, 0.8-4.2% fat, and are high in calcium (275mg/100g) and phosphorous (315mg/100g). Roasted seeds can be used as a coffee

The pods are a source of ethanol production. Pod yields of 2.5 tons of dry matter per Hectare (85 trees/Ha producing 30kg pods dry weight) would yield 730 litres of ethanol which is only 20% of that obtained from a hectare of sugar beet. As a sustainable and a low input source, though, it is much more viable.

Although a legume it does not fix nitrogen, they do accumulate minerals and are used in land reclamation schemes. The flowers provide nectar and pollen for bees. The honey yield are about 20-25 kg/ha of honey from a pure stand of trees.

Trimmed plants make a thick, impenetrable hedge and the trees are also extensively used as windbreaks in the great planes region of the United States.

The honey locust is tolerant of transplanting, heat, drought, air pollution, salt and high alkaline pH. It really prefers a continental climate and with warm summers and tolerates cold winters, being hardy to -32ÂșC and grow to about 4 meters in 10 years. The trees coppice and pollard well, and can be managed in these ways to provide sustainable yields of good quality firewood.

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