Amanda McNulty

Now is the time to start pruning

Amcnult @clemson.eduFebruary 27, 2014 

Crossing the Congaree and Wateree Rivers on my daily commute from St. Matthews to Sumter is like experiencing a living calendar. Right now Mother Nature is turning the pages of winter toward spring (occasionally losing her place and sending snow and ice) as signaled by the small but abundant flowers on the red maples happily growing in the moist floodplains.

In the maples and many other plants adapted to our part of the world, the root systems are awakening and mobilizing stored carbohydrates, increasing the concentration of dissolved molecules in those tissues. Osmosis results in water moving into the plant roots and pushing fluids upwards. The sap is rising.

Now is an ideal time to prune many of our woody plants. Pruning cuts are open wounds –an easy entry for insects and diseases. As the stored nutrients your plant made last year, when its leaves were green and the sun was shining, move back into the trunks and branches, those cuts can scab over and heal more quickly.

How you make those pruning decisions can speed up or slow down the healing process. If you’re removing whole stems or branches (a process called “thinning “as it doesn’t promote new growth), don’t make flush cuts – ones that are even with the trunk or large branch. There’s a yin and yang that goes on between conjoined stems and branches which have different diameters (i.e., the stem you are removing is noticeably smaller than the one it is attached to) that results in a swollen area of mingled cells botanists call the branch bark collar.

When you make a pruning cut right above, distally to, this slightly swollen area, you stimulate storage cells that release compounds with anti-microbial properties. The surface area resulting from this cut is smaller than from flush cuts so there’s a smaller wound to heal.

Pruning this time of year, when the plant is coming out dormancy, lets most of its reserves go towards making new tissue to protect the exposed areas – the plant isn’t trying to supply leaves, flowers, or fruits with huge amounts of water or nutrients like it will when the growing season really gets going. Cuts made too far above the branch bark collar result in a stub that will slowly rot and decay rather than heal cleanly.

The same principles apply to another type of pruning action called a heading cut — when you remove a portion of a stem or branch to make it shorter. Heading cuts actually promote growth from the development of previously suppressed buds near the cut end — buds that will become new leaves or shoots and make the plant thicker in that area. It takes a fairly long time before those new, tender tissues actually appear — hopefully after the last freezes that could harm them.

Here we aren’t concerned with a branch bark collar, but we do want to keep the size of the exposed wound as small as possible by choosing a shallow angle. Larger branches may have visible buds you can select to encourage new growth in a certain direction. For example, if you cut above an outward facing bud, the new shoot will result in a plant more open to sunlight and air movement. Make your cut a small distance above the selected bud so it won’t dry out.

The rule of thumb is to remove no more than one-third of the total canopy in any one year. However, occasionally older, established landscape plants get so mature and woody that they actually decline.

Our old-fashioned indica azaleas are an example. Decades old specimens often will profit from rejuvenation pruning although you’ll have to diligently refine their shape as long suckers will shoot up all over. Camellias, fruits trees, grape vines and others respond to yearly applications of a skillfully wielded blade with increased flowering and fruits. You can find all sorts of factsheets on how and when to prune in South Carolina at Clemson’s Home Garden and Information Center.

Prune artfully and when the knife is sharp.

Amanda McNulty is an associate extension agent for the Clemson University Cooperative Extension Service and the host of “Making It Grow!” broadcast weekly on ETV television stations. Website: www.clemson.edu/extension/hgic/ Check out her blog at the Making it Grow! page at www.scetv.org

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