Chapter 81 Caragana arborescens
81.1 Chinese pea tree
A pea shrub growing in open ground, showing a typical size and shape. Link to original image.
81.2 Soil: Lean Conifer Mix
Ratio: 2 parts bark, 1 part grit
Add-ins: dolomitic limestone (~5 lbs/yd); Tree-Tone (15 lbs/yd)
pH: ~6.5 (slightly below neutral)
Moisture: Fast draining
According to Hortus III (1976), pea trees grown for their flowers should be planted in sunny locations in sandy soil. Moderate water during growth. Keep soil fairly dry in winter. If the leaves turn yellow and fall, the tree is probably being overwatered.
81.3 Light
Routine: full sun. No additional precautions needed in summer.
81.4 Cultivation Notes
Pea trees are not common bonsai subjects but they they have a lot going from them: tiny leaves, yellow flowers, and mature grey bark. Pea shrub is known for being extremely cold, drought, and heat resistant.
It is a shrub or small tree ranging from 6-20 feet tall, In proper conditions new buds that break after pruning can extend 1-3 in a season. Both drought and cold tolerant, with a dense fibrous root mass that can fix nitrogen on its own, this species has been planted widely in the U.S. for windbreaks and for erosion control.
81.4.1 Potting & Root Pruning
Re-pot every two years in early spring before bud break.
81.4.1.1 Top & Branch Management
Heavy pruning: the tree can be radically pruned in winter. This also encourages profuse budding new shoots in spring.
Fine pruning: shorten new shoots after they develop 5-6 node back down to 2 nodes.
Wiring: best wired in winter while dormant. When wiring young shoots in spring or summer watch for marking; branches scar quickly.
81.4.2 Feeding
Every 2-3 weeks during growing season. Use a general purpose slow release fertilizer.
81.4.3 Pests & Problems
Chemical Warnings
81.4.4 Winter Storage
Store in mulch outdoors. Try to place in a shaded area so buds do not break in a mid-winter warm spell. No other special precautions are needed.
81.5 Propagation Notes
Seed is best sown as soon as it is ripe in a cold frame. It usually germinates in 2 weeks. Stored seed should be pre-soaked for 24 hours in warm water then sown in a cold frame. If the seed has not swollen then scarify it and re-soak for another 12 hours before sowing.
Germination usually takes place within 2 - 3 weeks at 70°F. Move seedlings to individual pots and shelter in a frost-free location for the first winter. for at least their first winter. Plant them out into their permanent positions in late spring or early summer, after the last expected frosts.
To grow them entirely outdoors, sow seed outdoors in autumn, or in spring after soaking the seed in warm water.
One North Dakota nursery grows Siberian peashrub by planting seed the last week in July or the first week in August. A cover crop of oats is seeded between the tree rows early enough to give winter protection. Shrubs are large enough to dig the following fall.
81.6 Artistic & Styling Notes
81.7 Additional Information
81.7.1 Natural History
Siberian peashrub is a woody legume native to Siberia and parts of China and neighboring Mongolia and Kazakhstan.