Caragana arborescens, or Caragana or Siberian peashrub, is a species of legume. It is a perennial shrub or small tree growing to heights of 2?6 metres (6 ft 7 in?19 ft 8 in). The plant is native to Siberia and parts of China and neighboring Mongolia and Kazakhstan. It is commonly grown throughout the northern hemisphere as a landscaping plant and ornamental. Typically, it has a moderate to fast growth rate, being able to grow one to three feet during the first year after trimming.

Caragana has pod fruits which contain many seeds. These ripen in July and if left, will fall off the shrub and the seeds will grow to become a new plant very near the parent shrub. The leaves of the caragana vary from light green to dark green and are alternate and compound with many small leaflets. Somewhat showy, small, fragrant, yellow flowers bloom in spring^[12].

Ecology

Ecosystem niche/layer

Secondary canopy or Shrub

Ecological Functions

Hedge

The plant can be grown as a hedge^[13].

Windbreak

It is quite wind-resistant and can also be planted in a shelterbelt; it is extremely tough and has been used as windbreaks on the Canadian prairies^[14][15]:252.

Earth stabiliser

The plant has an extensive root system and can be used for erosion control, especially on marginal land^[13]

Nitrogen fixer

Because of its nitrogen-fixing capacity, it is valued as a soil-improving plant^[6].

Ornamental

Somewhat showy, small, fragrant, yellow flowers bloom in spring. ^[12]

Forage

Chickens

The Siberian Pea Tree is oft cited as a good fodder plant to plan into a chicken run, orchard or field. If planted in with the chickens it drops good fodder straight into their foraging zone. The fruit is a pod which splits open when ripe, scattering the seed on the ground. The seed is released gradually over a number of months. In fact the chickens like the seed so much that they often can't wait for it to drop and do their best to fly up and pick it out of the pods^[15]:252.

Bees

A very good bee plant^[11]. The honey created has a pleasant taste, slightly 'fruity'^[12].

Shelter

Nothing listed.

Propagation

The seed is not dormant but may require scarification. It can also be propogated by semi-ripe cuttings in summer or by layering in spring.

Seed

Seed - best sown as soon as it is ripe in a cold frame^[14]. It usually germinates in 2 weeks^[16]. Stored seed should be pre-soaked for 24 hours in warm water then sown in a cold frame^[17][18][14]. If the seed has not swollen then scarify it and re-soak for another 12 hours before sowing^[19]. Germination usually takes place within 2 - 3 weeks at 20°c^[19]. Good percentage^[3]. As soon as they are large enough to handle, prick the seedlings out into individual pots and grow them on in a greenhouse for at least their first winter. Plant them out into their permanent positions in late spring or early summer, after the last expected frosts. There are approximately 40,000 seeds per kilo^[6].

Rooted cuttings

Cuttings of half-ripe wood, 7 - 10cm with a heel, July/August [Britain] in a frame^[18].

 

Cultivation

Succeeds in most well-drained soils, preferring full sun and a light sandy dry or well-drained soil^[20][3][14]. Tolerates very alkaline soils^[4]. Plants do not require a rich soil^[20][3][21], succeeding on marginal land^[13]. Established plants are drought resistant and fast growing ^[13][22]. Annual water requirement: 305mm - 1397mm^[23]. Dormant plants are hardy to about -30°c^[24], they prefer a continental climate and do not grow so well in areas that do not have very cold winters^[14]. They grow and fruit very well in the eastern half of the England, even in northern areas, though they do not do so well in the wetter west^[16]. The young growth in spring, even on mature plants, is frost-tender and so it is best to grow the plants in a position sheltered from the early morning sun.

The Siberian pea shrub has an excellent potential to become a staple food crop. The seed is nutritious and wholesome, although rather small it is often very freely borne and is easily harvested^[16]. This species has also been recommended as a nitrogen-fixing windbreak and ground cover plant that binds the soil and produces fibre and dye stuffs^[25]. Caragana boisii and Caragana fruticosa are closely related to this species^[26].

A very ornamental plant, some named forms have been developed for their ornamental value^[26]. 'Nana' is a very compact dwarf form^[5] that grows slowly^[3]. 'Pendula' has stiffly pendent branches but is otherwise the same as the type species^[3].

Plants in this genus are notably resistant to honey fungus^[14]. This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby^[14].