Developing a flowering deciduous bonsai is done in a radically different manner than nursing a conifer. Conifers needs their needles all the time, and if you cut back a branch lower than the needles are present the branch will certainly die. But branches can be bend and placed and thereby often a more “instant” result is achieved. Deciduous trees and shrubs needs a totally different approach. You have to think at least five to ten years ahead when you make even the most drastic pruning. Because what is not there when you remove it will be build up later.
This Spiraea has been an experiment ever since I bought it as a rather cheap raw nursery stock in 2006. I didn’t know of any Spiraea grown successfully as flowering bonsai, and had settled early with the consequence of training this specimen as a deciduous leaf bonsai without flowers. Because the very small leaves are pretty good for shohin alone.
After seven years of training a good canopy has been developed, and I decided to try out how to develop flowers, well knowing that the speedy growth of this type of tree, may or may not be impossible to keep in a good shape and still get into flower. The trick is to follow a pruning regime pretty hard. Cutting the branches back hard in spring (after flowering or in May), and then pruning lightly until end of June app. The Spiraea develop its flowers on the growth of the previous year, so in August and September (Northern Europe conditions), it is left to grow and develop flower buds on the growth at this time. Only very light pruning is done, and being aware that potential flower buds are in risk of being pruned away from late summer and onwards.
Feed well in spring and summer and slow down in autumn. When a dense root system is developed over some years the long rapid growth will reduce and make it easier to keep in shape.
Read more about this tree at the step-by-step article at https://shohin-europe.com/PROGRESSION-Spiraea.htm