Rules of Thumb for Pruning Shrubs


Pruning is the source of confusion and worry for many gardeners.  How and when to prune are the two most common questions asked by new gardeners.  Luckily, there are few simple guidelines that provide good advice for pruning a variety of flowering shrubs. 


Rule of Thumb Number One: Do not prune.  Many gardeners believe that they must prune regularly to keep their shrubs in good condition, this is not true.  Most shrubs need only one significant pruning session a year and many do not need any pruning at all. Pruning common shrubs like lilacs, forsythias and burning bushes is not only unnecessary, but is not good for the plants.  Many flowering shrubs will look their best when they are allowed to grow naturally.  Frequent shearing encourages lots of surface branching, possibly resulting in unhealthy structure and reduced flowering.  If you really want a tightly sheared look in your garden, choose a plant that is meant to be pruned, such as boxwoods. 


Rule of Thumb Number Two: Prune spring flowering shrubs after flowering.  Plants that bloom in early spring usually produce their flower buds the year before and over winter, which is called blooming on 'old wood'.  If you prune these spring bloomers in fall or winter you will remove the flower buds and you will not have flowers that year.  The plants will be OK, but you will miss a year of blooms.  Most of these plants do not need heavy pruning every year, just some selective thinning of branches to give them a nice shape. 


Rule of Thumb Number Three: Prune summer flowering shrubs in late winter or early spring.  Many summer flowering shrubs bloom from the growth of the current year, which is called blooming on 'new wood'.  Pruning them back in later winter encourages them to produce many new buds that summer which will result in more flowers.  Do not be afraid to cut fast growing plants, such as buddleias or caryopteris, down to as little as 10-12" tall.  The exception to this rule is hydrangeas (see Rule of Thumb Number Four).  


Rule of Thumb Number Four: Hydrangeas.  Hydrangea questions account for at least half the pruning questions on gardening advice forums.  Some bloom on 'old wood' (Rule of Thumb Number Two) while others bloom on 'new wood' (Rule of Thumb Number Three.)  You will need to identify what kind of hydrangea you have and follow the appropriate rule.  Hydrangea macrophylla, the ones with big blue or pink flowers, Hydrangea quercifolia and oakleaf hydrangeas bloom on 'old wood'.  The little pruning they need should be done immediately after flowering.  Hydrangea paniculata, which have white, conical flowers and Hydrangea arborescens, bloom on 'new wood' and will produce better flowers if cut back in late winter.


Rule of Thumb Number Five: It is OK to trim anytime.  Gardeners are often confronted with stray shoots and branches in late summer and worry about removing them.  Go ahead and cut them back, plants will not be damaged by removing a branch or two.   
   


With these five rules of thumb you can relax knowing your landscape plants do not need as much pruning as you may think.  If you would rather go to the beach than shear back your landscape plants, go right ahead.  The only potentially tricky part of pruning is determining when to trim a particular plant.  For a quick review, prune summer bloomers in late winter and spring bloomers right after flowering, remember to check the hydrangea rule (Rule of Thumb Number Four) before you trim, and stray or broken branches can be trimmed anytime.  If you do make a mistake, plants are very forgiving, you may miss a season of flowers but the plant will recover for the next year.

- Proven Winners

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