The Siberian pea shrub (Caragana spp.) is one of the toughest landscape plants -- tolerant of extreme heat, cold, drought and wind, and almost any soil type. It can be grown in U.S. Department of Agriculture plant hardiness zones 2 through 9, but is most common in the northern half of the country. The shrubs have a dense, upright habit and beautiful sprays of small yellow flowers in spring. A little annual pruning goes a long way in bringing out the best form and most profuse flowering in caragana.
1 Remove any "suckers" that grow from the base of the trunk. These make for an awkward appearance if they are allowed to remain.
2 Prune off lower branches to create more of a tree form, if desired. Caragana has an upright growth habit and can reach 20 feet high. Removing the lower branches to a height of 4 or 5 feet makes a more attractive form for a single plant. This type of pruning can be done at any time of year; just make sure to cut the branches back flush with the main trunk.
3 Prune the canopy of the siberian pea shrub in summer after the flowers have faded. This will clean up the appearance of the seedpods, which turn brown and look messy. Use hedge shears or an electric hedge trimmer to evenly trim the canopy back 6 or 8 inches into a uniform shape. If desired, trim once a month in this fashion for a more formal looking hedge.
4 Remove any long, single stems that grow awkwardly from the main canopy whenever they appear. The shrubs have a naturally dense and uniform growth habit, but long sprouts occasionally appear and should be cut back all the way to the large branch they are attached to.
5 Cut down the central trunk of tall specimens with a pruning saw if they grow above the desired height. The cut should be made about 2 feet below the desired height. Caragana can be maintained at 8 or 10 feet tall and will tolerate a drastic cut if they get out of hand. This should be done in late summer or fall to minimize stress to the plant.