Japanese spiraeas tend to form round or sometimes oblong mounds, which are not completely tidy. If left unsheared, they can expand up to 1 m tall and wide, therefore I suggest – be ruthless and shear them back on a regular basis. As a result their foliage will be brighter, while flowers will be larger. I personally value colorful foliage above flowers. Flowering of trees and shrubs is fleeting, while cultivars with colourful foliage often produce very few flowers, if any at all.
Having said that, golden-leaved Japanese spiraeas are breathtakingly beautiful in flower – their flower heads appear just as the spring foliage fades. The flowering continues for 10 to 20 days (depending on weather – in hot and dry weather the show is very fleeting). I remove spent flower heads promptly, before they fully finish flowering. At the same time I prune the plant into shape, since by midsummer it often becomes quite lax. Pruning is a very straightforward process – I grab a handful of branches and shear them back by 5-15 cm (yes, that much, especially in the rock garden). I go this way all around the bush.
After I shear spiraeas, I normally end up with a barrowful of cuttings. They can be disposed of, or alternatively they can be rooted. End of June or beginning of July is ideal for propagation by semi-woody cuttings, besides japanese spiraeas root easily. For this purpose take 7-15 cm long non-flowering branches, remove their soft tops, and insert them into pots with fertile moist garden loam. Keep the pots in a shaded place (I keep them on the north side of the house under hostas). Do not forget to keep them evenly moist. I usually forget the cuttings until the autumn, however, this is not an example I suggest you follow. The success rate of this lazybones way is around 70 percent.
Like I mentioned, these are very tenacious plants. I have planted and transplanted mature spiraea bushes numerous times, moved them from one place to another at a wrong planting time, forgot to water them – but they invariably take root. The only thing that I do after transplanting spiraeas, is to shear back bushes by 2/3 rds. I simply remove all growth to within some 20 cm from the shrub centre. This way plants loose less water, and as a result they root easier. A year or three later spiraeas spring back to their normal size.
Spiraeas can be propagated by woody cuttings – in late autumn (after the leaves have fallen) or early spring, before buds break dormancy. Collect 10-15 cm long cuttings, remove their soft tops, and insert them into a pot with ordinary garden soil. Keep in the garage or cellar. The only thing important is that the room is frost-free. Insert the cuttings into the soil so that two leaf nodes were covered and compact soil around them.
I use this method to propagate spiraeas in autumn, since spring is extremely busy time in the garden. I keep the soil moist, and take care to throw some old rags on top (my garage is unheated) or move them into the cellar if hard frost is forecasted. The cuttings require no light until spring.
If only 1-5 new plants are necessary, the easiest way is to produce them by layering. In early spring, before plant breaks dormancy, choose a young flexible branch. Make a shallow trench close to the mother plant. Lay the branch into the trench, pin it down with wire or plastic pegs to keep it in place. Cover with some more soil, and compact it gently. 1 or 2 buds or bud pairs should be covered with soil, leaving the tip of the branch above the ground. Normally, there is no shortage of moisture in spring, but in summer do remember to water before the soil dries out. In autumn pull at the branch gently – if it does not give easily, this means that the branch has rooted. Cut the branch from mother plant, however, wait until spring before removing it and planting it elsewhere.
[banner] As for planting site and soil type, spiraeas are very obliging. However, if you have a colourful spiraea cultivar, make sure you plant it in a sunny spot, where it would receive at least half a day of direct sunlight. When grown in shade foliage will not be as bright, and the plant may even revert to green. In contrast to majority yellow leaved plants, spiraeas almost never burn in strong sunlight, unless they are grown in pure sand. As for soil type… unfortunately, I do not have any experience of growing spiraeas in sandy soil, I can assure that anywhere else – be it rich compost or heavy clay – they simply thrive. I do not additionally fertilise them during the season – in spring all my trees and shrubs (apart from conifers) get their ration of slow release combined fertiliser, and that’s about it. True, I amend soil with well-rotten grass clippings (sprinkling them around plants), but I am not so generous with spiraeas. As a matter of fact, they thrive on neglect.
© Giedra Bartas, 2015