Spirea is a beautiful, rich green shrub, but like all other types of shrubs, you will have to know how and when to prune these plants. When properly cared for, spirea will grow lovely, tiny, delicate lavender flowers. They are a wonderful addition to any garden and are relatively easy to grow and care for.
Spirea shrubs should always be pruned in the spring, after they bloom. Pruning is necessary in order to maintain the plant's maximum overall health as well as for shaping, as growing too wild can hinder the shrub's growth or the growth of offspring spirea. Once per year should suffice, and you can prune those spireas that are older and are in need of reinvigorating or for just shaping. Pruning spireas immediately after blooms appear enables the plant to create new wood for the following year's flower production. Check to see what kind of wood grows on your spirea if you don't know the particular type you have.
For the actual pruning, you should use a good pair of lopper or hand pruners. Always remove old canes from the shrub at their bases. When the spirea matures and produces less flowers, cut back on the amount of pruning you do by at least 30 percent. This will help to stimulate new growth in your shrubs. If you are pruning newer and more compact growths, reduce your cutting to about four to six stems so that they can be renewed.
Summer-blooming spirea shrubs are ideally pruned in the early spring, prior to the blooming period. Pruning them during this time will encourage new and healthy growths and increases the number of blooms your spirea will produce. Be sure to remove at least half of the shrub's old growth, and cut the oldest branches first and foremost, as these will not produce any additional blooms.
If you are experiencing a time of drought in your area, you should water your spirea shrubs adequately. In general, the plant doesn't require an inordinate amount of watering, and pruning can take place without watering except during droughts and especially dry periods and in the late fall, prior to freezing temperatures leading into the winter season. When you do water, administer at least a gallon of water or use your garden sprinkler system for about 20 minutes two times per week.
Spirea shrubs also require a good amount of mulch, so if you are hoping to see good blooming on it, apply a good slow-acting fertilizer and plenty of compost material for mulch. This will encourage more growth from your spirea plants, and you will have plenty to prune when the time is right.
If you are pruning simply for shaping purposes, take a good, long look at your spirea. Envision what kind of shape you think would look best on the shrub, and decide whether it would work in your garden or porch. If you can visualize it and think of it as favorable, use some wire to hold the shrub into a particular shape. This will better enable you to prune it to that shape as you cut the portions that escape the wire template.