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Dormant season pruning

  • James Campbell
  • In my dream garden, every plant would mature into the perfect size and shape for its spot. But, as anyone with a garden knows, this is not how it works. Most plants require periodic maintenance and a little guidance to be their best. This maintenance includes pruning which is a pretty complex topic! No set of rules covers the pruning of all trees and shrubs. It is best to consider each plant individually and in its place in the landscape.

    Dormant season refers to the period when the plant is not actively growing. Dormancy is easy to recognize in deciduous trees; this is when they lose their leaves. Evergreen trees also go dormant and stop growing even though they retain their leaves. Dormancy is when a plant is not making leaves, flowers, fruits, and seeds. Pruning a dormant woody plant allows them to focus on healing because it is not growing new leaves and branches. 

    California natives like this Buckeye in Tiburon may look dormant, but it is about to bud. Photo: James Campbell
    California natives like this Buckeye in Tiburon may look dormant, but it is about to bud. Photo: James Campbell
    While winter is the dormant period for many plants in our gardens, many of our California native plants go dormant during the heat of summer. There are some general rules to follow when choosing a time to prune.  Prune spring or winter-blooming trees and shrubs after their bloom cycle is complete. These plants bloom on old wood, and if you prune them in the winter, you will destroy the flower buds and lose the bloom season. Summer or fall-blooming trees and shrubs should be pruned during dormancy, in most cases, in the winter. These plants bloom on new wood.

    Some plants bloom on both old and new wood. First on the old wood and then again later on the new wood. These plants should have limited pruning after the first bloom. Heavy pruning may remove too many leaves and deprive the plant of its ability to generate enough energy for new growth and new buds. Ceanothus, Strawberry tree, Tea tree, Lemon, and Loropetalum are examples of plants that bloom on old and then new wood.

    Lorapetalum is a plant that blooms on both old and new wood. Photo: Scott Zona
    Lorapetalum is a plant that blooms on both old and new wood. Photo: Scott Zona
    While there are exceptions to every rule, conifers or needle-leaf plants are not tolerant of heavy pruning. Sheer new growth in the spring to make the plant denser. Limit conifer pruning to removing dead or injured branches and, if possible, allow conifers to develop their natural shape. Avoid pruning pines in the summer when the resins will attract beetles.

    Fruit tree pruning has its own unique rules. In addition, each fruit tree is different, so check the specifics for the fruit tree you are pruning.

    Master gardeners have come up with some pretty handy rules of thumb for approaching pruning. Wood that you can remove at any time of year is the three D’s: dead, damaged, or diseased. Remember not to prune oak trees when they are most susceptible to the sudden oak death pathogen during the spring.

    After this Japanese maple sheds its leaves, it is easy to see which branches are rubbing. Photo: James Campbell
    After this Japanese maple sheds its leaves, it is easy to see which branches are rubbing. Photo: James Campbell
    Pruning best done during the dormant season is the three C’s: crowded, crossing, or competing (for the same space in a plant).

    The three S’s are pruning goals based on the plant’s location in the landscape: sight lines, shape, and safety. Remember the basic principles of fire-safe landscaping when pruning your shrubs and trees,  https://ucanr.edu/sites/MarinMG/files/356387.pdf.

    A rule of thumb is to remove no more than one-third of a shrub or tree, but pruning is very much plant-dependent. If the plant is old or diseased, or compromised in any way, remove less than a third. Some plants may not tolerate removing a third, and others may tolerate removing more than a third.  It is a good policy to know the particulars of the tree or shrub you are pruning. Remember, you may not accomplish your goal to reshape a plant in one pruning session, so make a plan you can carry out over two or three years.

    For more advice on pruning plants, visit the Marin Master Gardener website at marinmg.ucanr.edu.