Colutea

Colutea

Colutea arborescens ( Bladder Senna )
A rapid growing, open, rounded, small tree reaching around 20 feet, that is native to southern Europe. Some records include: 1st year - 4 feet; 20 years - 23 x 10 feet; largest on record - 40 x 20 feet. This tough, attractive plant is great for use along highways.
The leaves, up to 8 inches in length, are composed of 5 to 7 pairs of leaflets, up to 2 ( averaging 1 ) inches in length. The foliage is bright green.
The small, golden-yellow flowers, up to 0.7 inches, are borne late spring through the summer.
The flowers are borne on current season wood.
They are followed by bladder-like pods, up to 3 x 1.5 inches, that are bright green ripening to red. The papery pods ripen during late summer and persist through fall and burst loudly if squeezed.
Hardy zones 4 to 8 ( reports of 3 ) in full sun to partial shade on sandy, well drained soil. Heat and drought tolerant and does not like excessive wetness. Despite its natural range, it proved hardy in plant trials at Dominion Arboretum in Ottawa, Canada. It may be prone to aphids in some areas. It can be cut back hard during winter for size control and renovation. Propagation is from seed sown during autumn or softwood cuttings taken during summer. The seed should be soaked in sulfuric acid for up to 2 hours then washed under cold water for 15 minutes before sowing at 0.25 inches deep.

* historic archive photo

Colutea buhsei
An extremely rare shrub, reaching up to 17 feet, that is native to Iran.
The pinnate leaves are composed of 7 to 9 leaflets. The foliage is blue-green.
Up to 7 large, golden-yellow flowers are borne on a raceme.
Hardy zones 6 to 8.

Colutea istria
A medium size shrub that is native to the Middle East.
Some records include: 2 years - 6 feet; 3 years - 7.5 feet; 5 years - 9 feet; largest on record - 10 feet.
The leaves, up to 1.5 inches in length, are composed of 3 to 6 pairs of narrow drooping leaflets, up to 0.5 inches in length.
The yellow flowers are borne in clusters, up to 3.2 inches in length.
They are followed by fine hairy seedpods.
Hardy zones 7 to 10

Colutea x media
A vigorous, open, rounded, medium size shrub that is the hybrid between Colutea arborescens & C. orientalis. Some records include: largest on record - 10 x 13 feet.
The leaves, up to 6 inches in length, are composed of up to 13 leaflets, up to 0.5 inches in length. The foliage is brownish-red at first, turning to blue-green.
The orange to light reddish-brown flowers are borne on racemes all summer long.
They are followed by reddish, bladder-like seed pods, up to 2 inches in length, during late summer into autumn.
Hardy zones 4b to 9 in full sun to partial shade on just about any well drained soil. Very drought tolerant. Unlike other Coluteas, this one does not enjoy excessively hot summers but has been found to be hardy at Dominion Arboretum in Ottawa, Canada. It can be cut back hard during early spring for size control or renovation.
Propagation is from softwood cuttings taken during summer.

Colutea orientalis
A medium size shrub native to from northern Iran to southern Russia. Some records include: largest on record - 10 x 7 feet.
The leaves, up to 4 inches in length, are composed of up to 9 leaflets, up to 0.5 inches in length. The foliage is blue-green.
The yellow & orange-red flowers are followed by seed pods, up to 2 inches in length.
Hardy zones 5b to 9 ( tolerating -20 F ) in full sun to partial shade on fertile, well drained soil with regular summer water. Tolerant of seashore conditions.

Colutea persica ( Persian Bladder-Senna )
A shrub that is similar to Colutea arborescens but is smaller and more compact in habit. It is native to Iran. Some records include: 3 years - 5 feet.
The foliage is silvery-blue.
The flowers are yellow.
Hardy zones 4b to 8, it tested hardy at plant trials at Dominion Arboretum in Ottawa, Ontario.