AFTER a long, wet winter there's one particular group of plants that will be in need of special attention in spring.
Plants like rosemary, sage, lavender, rock rose (Cistus species) Russian sage (Perovskia species), wormwood (Artemisia species), thyme and several other sub-shrubs can look a little tattered and tired after winter.
Those plants are classified as sub-shrubs, which are small low growing shrubs that do not produce hardy, thick and robust woody stems. Not to be confused with tender shrubs like abutilon, sub-shrubs are generally hardy and grown outdoors but they suffer winter damage when they are grown in wet climates like ours and therefore need pruning in spring to rejuvenate their structure.
Lavender, for example, will usually come through the winter with only minor damage on the tips of the stem and the spring cleanup usually involves trimming the tips back lightly. Light trimming, however, only promotes dense upper growth at the expense of lower basal growth found on the older wood.
After successive years of shearing, lavender will become sparsely foliated near the ground and densely branched at the stem tips leading to a leggy looking appearance.
Shearing - as I have said before - is for hedges, not for every tree or shrub in the world that grows too big because it is planted in the wrong place.
Almost all sub-shrubs suffer legginess over time if they are not pruned to correct the situation. Part of the problem of managing all sub-shrubs is our predisposition for shearing instead of applying real pruning techniques to deal with the leggy growth.
While it is true that constant hard pruning of any plant will generally lead to an early demise, sub-shrubs need a strong hand from time to time to guide their development.
Sub-shrubs will exhibit symptoms that indicate when it's time to prune hard instead of shearing. There will be new growth at the top of the stems but look down into the centre of the plant at the lowest part of their stems and identify new buds emerging from the older wood near the ground.
Sub-shrubs will not produce new basal growth every year, especially when they are young or growing under optimum conditions. But as those shrubs age their new growth will cluster near the top of the stem where everyone usually shears.
At the same time there will be growth down lower on the older part of the stem near the base of the plant, which is exactly where sub-shrubs should be pruned once every three to five years.
It may seem drastic to cut back a lavender or rosemary by three quarters of its height, but it must be done as prescribed if you want to avoid a sparse or leggy looking appearance or premature death. Failure to prune as prescribed eventually leads to thickening of the bark on the older stems which then prevents new buds from developing down near the base of the plant, and ultimately permanent legginess and a gaunt appearance.
That's a lot of descriptive analysis of sub-shrub growth so let me give you a simple step by step process for pruning sub-shrubs in spring. Firstly, be sure your plant fits the definition of a sub-shrub, or perhaps it is one of the plants listed herein.
Secondly, look at the plant's growth and notice if it is producing new buds down lower on the stem near the ground, or, if it is only producing growth near the top of the stem. If there are only buds and new growths near the top of the stem it is less likely to respond to hard pruning. If there are buds emerging down lower on the main stems and there is sufficient number of them, you can safely prune hard, reducing the plant's overall height by half to two-thirds of its overall height depending on where the buds are emerging.
Thirdly, as warranted, cut back down low, pruning just above each new bud. Try to prune to give the woody framework that remains a gentle mounding form which will produce a graceful and natural form during summer. Always prune using a square cut. Angled or sloped cuts are for amateurs. Since all of the plants mentioned herein produce flowers on the terminal ends of the current season wood, you can prune in the manner prescribed and still have lots of flowers, with the added benefit of developing a low growing and well branched plant.
Part of the reason for applying reconstructive pruning on sub-shrubs is to prevent a gaunt appearance and prolong their life span.
As always, use clean, sharp Felco hand pruners to make the best cut possible. And don't be scared to make cuts if the conditions are right.
Remember, no guts, no glory.
Todd Major is a journeyman horticulturist and chief horticulture instructor at the University of British Columbia Botanical Garden. For advice contact him at stmajor@shaw. ca.
