Spiraea
is a genus of around 80 species of deciduous or semi-evergreen
shrubs found in rocky places, thickets and woodland. Widely distributed
in northern temperate regions of Europe, Asia and North America
including Mexico. Spiraea have alternate leaves that are entire,
toothed or lobed and in many species are decorative.
Two Spiraea
species are commonly used for bonsai, S.japonica and S.thunbergii.
Spiraea
japonica
Spiraea japonica is a clump forming, deciduous shrub with erect
shoots, native to China and Japan where heights of around 2metres
are reached. It has ovate, sharply toothed, dark-green leaves
to 10cm long. In mid- to late-Summer, it bears bowl-shaped, pink
or white flowers in terminal corymbs to 20cm across.
As a popular garden shrub, Spiraea japonica has a large number
of varieties which carry varying leaf and flower colours.
Spiraea
thunbergii
S. thunbergii is a dense, bushy, deciduous or semi-evergreen shrub
with arching branches and slender, lance-shaped, sparsely-toothed,
light-green leaves to 4cm. In Spring and early Summer, it bears
bowl- or saucer- shaped white flowers in clusters to 5cm across.
Native to China and Japan where heights of around 1.5metres can
be reached.
BONSAI CULTIVATION
NOTES
POSITION Full sun.
Frost hardy to -10°C.
FEEDING Every two weeks
throughout the growing season.
REPOTTING Every two
years in Spring as buds extend. Use basic soil mix.
PRUNING Spiraeas produce
numerous long arching shoots from old wood in Spring and these
need to be pruned back hard or removed to keep shape. After this,
pruning should be stopped to allow flowering to occur.
After flowering, prune
back repeatedly to shape through the remainder of the season.
Deadhead spent flowers. Once branches have hardened and lignified
they become very brittle; wire whilst shoots are still young.
PROPAGATION Take greenwood
cuttings in Summer and hardwood cuttings in Winter.
PESTS AND
DISEASES Trouble free though mildew can be a problem in warm,
damp conditions, if so provide a position with better air-circulation.
STYLING Suitable
for informal upright, slanting and cascade forms in extra-small
to medium sizes. Particularly suitable for clumps or root connected
bonsai.
