Tuesday, 7 May 2013

Siberian pea tree (Caragana arborescens)

The Siberian Pea Tree is a hardy deciduous shrub or small tree native to Russia and China. Also known as the Siberian Pea Shrub or Pea Shrub. They are often grown in the British Isles as an ornamental and there are different forms including dwarf, upright and pendulous. They are currently (May/June) in flower in the British Isles so look out for the yellow flowers.

An image of the flowers and leaves of the Siberian pea tree (Caragana arborescens)
Siberian pea tree (Caragana arborescens)

The Siberian pea tree was introduced to North America in the mid-1700s and has become established in most of Canada and around half of the states in the USA. They are now considered an invasive species in some areas of North America.

Growing methods

Sow seed in the spring. Scarify and soak seed overnight. Sow around 2 cm deep in a seed bed or pots. Press soil down firmly. Seeds should germinate at around 20°C within 2-3 weeks. Prick out seedlings and pot on when large enough. Plant out the following spring.

Shrubs sown from seed should begin to crop in 3-5 years time. The flowers bloom in May or June and the pea pods ripen in September. A mature shrub produces a prolific amount of seed and when the pods are ripe seeds will disperse around the base of the shrub to produce more plants.

Siberian Pea Tree (Caragana arborescens)

Shrubs can be pruned back to as much as 10 - 30 cms from the ground (to grow as a bush) or left to their own devices to grow naturally. They can grow up to around 6 metres in height although they are more often smaller in the British Isles. Shrubs are long lived, very hardy and generally not affected by frost. Whilst they prefer a sunny position, they can tolerate a strong winds and drought conditions. One reference said they do well in maritime areas, another said not. For best results the soil should be kept dry or moist.

A review of the biology of the Siberian pea tree in Botanical Studies (2012) states that:
"Caragana arborescens is known for its tolerance of many environmental conditions including droughts, temperatures to -38°C, infertile soils, sunny sites, high winds, alkaline soils and saline conditions (Henderson and Chapman, 2006; Dietz et al., 2008; Martine et al., 2008; USDA NRCS, 2010)"

Other uses

These shrubs are a nitrogen fixer initiating nitrogen fixation at temperatures of 3-5°C, which is lower than many other plants. They have an extensive root system so can be planted to counter soil erosion. They can also be used as a wind break. They are less attractive to being eaten by predators as they produce the toxic non-protein amino acid L-Canavanine. The flowers attract pollinating insects and are particularly liked by bees. Cordage can be made from the bark. An azure dye can be made from the leaves.

The genus Caragana is used in traditional Chinese medicine and is considered a remedy for many ailments.

Raw edible parts

An image of the flowers of the Siberian pea tree (Caragana arborescens)
Siberian Pea Tree (Caragana arborescens)

The pretty yellow flowers and very young green pods are edible raw. This is a legume so it is probably wise to eat pods raw in moderation. The older pods are also edible but should be cooked. Both flowers and pods have a pea flavour and are good in salads. The seeds, which are similar to lentils, and can be used in the same way, also produce an edible oil.

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