The easiest way to remember when to prune your shrubs is to do so right after the plant blooms. You may even get a second flush of blossoms, especially in Spirea, Weigela and Potentilla. You will also encourage more growth from the side buds. Prune your shrub right away if you notice:
Dead branches – if completely dead, remove the branch right to the ground, otherwise cut back to where it joins the main stem.
Crossing branches that rub – remove one, so that they do not damage the bark, leaving a wound that is susceptible to disease. If the branches are not yet rubbing together but will be shortly, use your judgement – you may be able to wait until you shape the shrub.
Shaping a shrub can include a gentle trimming for esthetics or rejuvenating a shrub. Pruning won’t keep a six-foot bush at 3 feet – you’re better off transplanting the larger-than-you-expected shrub somewhere else in your garden or giving it to a friend!
Pruning for esthetics is a slow process: remove one branch or portion of a branch at a time, and stand back between cuts to ensure the shrub is still balanced. When you prune, you stimulate growth at the buds, so try to prune to an outside-facing one. This encourages the new branch to develop outwards, letting the sun get into the middle of the shrub and encouraging air circulation. Often you need to remove only a few of the oldest and thickest stems at the ground to thin out the shrub. If you are pruning to reduce the size of your shrub, always remove the branches to where they join the main stem.
Use a sharp pruning saw and a pair of bypass pruners or secateurs. Hedge shears tend to create an unnatural looking shrub, spoiling its form, interfering with the natural growth of the shrub, keeping light from getting into the centre of the plant, and discouraging air circulation.
Try rejuvenation pruning to get an out-of-hand shrub back under control. Cut the oldest and thickest branches right down to the ground – not exceeding one third of the overall number of branches – and distribute your cutting throughout the shrub. The second year, tackle the second third of the shrub – and in the third year, do the finishing touches.