Spring Pruning Can Hurt Your Tree’s Bank Account

The beautiful warm weather this past Wednesday created an irresistible opportunity to get outside and observe the awakening plant world.  Woodland wildflowers are starting their spring show, which will peak over the come month or so.  The swelling, pink buds of redbud are a sure sign of the flowering display that will ensue in coming weeks.  In my landscaping, it was nice to see daylily patches and fall-planted bulbs start to push up those vibrantly green first leaves of the year.  Although a little too wet for much work, my vegetable garden is awaking with some unwanted green from the first weed pressure of the season. 

All of these plant signs of spring, combined with warm and sunny weather motivates gardeners to get busy this time of year.  I would imagine that many of us were out in force on Wednesday prepping our gardens and yards for the many nice days ahead.  As we start to make the spring rounds it is always very tempting to prune woody plants in the process.  However, pruning during spring bud break or flowering can be an incredibly damaging practice for trees and shrubs.

As with herbaceous vegetation, the spring awakening for woody plants is an energy intensive process.  The first sign of this energy investment can be seen in swelling buds, indicative of the coming leaves or flowers.  Pruning after bud break removes these plant structures, removing energy from the plant at the same time, which can ultimately impact plant growth and vigor in the coming year, especially on an already stressed plant.

A woody plant relies on its collectively stored energy in roots, buds, stems and other plant tissues to break dormancy and begin growth for the year.  This energy was generated the previous year as leaves photosynthesized to produce energy-infused sugars.  Although many of these sugars are used for the immediate needs of the growing season, a healthy woody plant is able to produce some sugars beyond the daily demand.  This excess energy is stored away to fuel next year’s spring awakening. 

The annual energy production of woody plants is often explained in terms of a savings account.  During summer, as leaves are actively photosynthesizing, energy is being stored away or saved.  As fall time rolls around, trees save every penny to squirrel away for winter.  Although they may make a withdrawal from their savings account to perform the energy intensive process of leaf drop, they make sure to remove every last bit of energy possible from leaf structures and put it in savings. 

When spring rolls around, it is time for a major withdrawal to invest in the plant parts that will fund energy production during the coming growing season.  The start of this energy investment can be observed this time year as buds start to swell.  Flowering is a costly process as well that will demand a large spring withdrawal.  After all, the process of flowering, pollination and subsequent fruit production is what perpetuates a species.  In the grand scheme of things, it’s well worth the energy investment!

Pruning in spring removes a large amount of a woody plant’s savings before it can replenish those funds with its new crop of leaves.  The general recommendation is to wait until leaves have fully developed and had a chance to photosynthesize (around mid-June) and make a return on their initial investment.  The best pruning strategy is to wait until winter dormancy.  Your plant has stored away as much energy as possible and the plant parts removed will ultimately have less impact on your tree’s bank account.

The bottom line is that you can prune off a troublesome limb or two this spring, but just realize that your plant’s annual budget is taking a loss from the energy you removed.  If earnings from last year can absorb that loss, it may not be a big deal. In many cases, I would say prune away on that one limb.  However, if last year was a bad year, or you plan to prune the entire canopy, you may be removing more than your plant can afford.