Get more out of your garden by understanding and applying this trio of techniques.
By Oscar H. Will III
Photo by Getty Images/Kudymov
Folks have been messing with plants long enough to have discovered that those very plants might serve human needs better if their physical growth were restricted in a more or less systematic way. In some cases the plants might grow taller, or shorter, or with a different shape; in other cases they might produce more fruit or flowers. Some manipulations are even designed to enhance fruit ripening, or simply to add some visual statement to the plant’s growth habit.
Three of the most common techniques that gardeners use to manipulate their prized flowers, fruits, and vegetables are pinching, pruning, and deadheading. All three of these activities are actually some form of pruning, but each is employed for a specific outcome.
Photo by Casey Marshall
As a very specific type of vegetative pruning, “pinching” is the actual pinching off of the growing tips on an herbaceous plant, such as the annual petunia (Petunia spp.). When the plant is in the vegetative state, the removal of all growing tips (up to a couple of inches from the apex) removes the dominant apical and axillary meristems for that particular shoot or branch. A complex cascade of chemical signaling then activates inactive axillary buds, causing them to grow into shoots or branches. In some plants, those activated buds will compete, teleologically speaking, to give rise to a new apical shoot — which then, through another cascade of chemical signaling, reduces its contenders to a life of axillary service.
So let’s take a look at an old, open-pollinated or cutting-reproduced petunia. When you start the cutting or germinate the seed, you’ll have a plant with a single apical shoot and a few axillary shoots branching off below relatively quickly. Notice that the longer axillary shoots are nearer the bottom of the apical shoot. This is due, in part, to a chemical gradient that’s emitted by the meristematic tissue growing and differentiating at the apex. Now, when you pinch that apex, or even the tips of the axillary shoots, you’ll stimulate branching of your petunia plant, which will reduce legginess and generally cause the petunia to grow into a bushier specimen, with many more branches upon which flowers will form. Cool, eh? This technique also works with most modern petunias — even the cascading types, although they’ve been developed to flower profusely without any help. Not all plants respond this way to pinching, but most herbaceous annuals and many perennials do, as long as they’re not rosettes. Woody species can technically be pinched to some advantage, but it makes more sense to use shears or pruners, and pinching woody species is generally done to enhance the plant’s bushiness.
Photo by Casey Marshall
Deadheading is the practice of pruning spent blossoms from the plants upon which they were borne. While there’s lots of lore and teleology surrounding deadheading, the practice is useful in a couple of ways, depending on the plant. First, deadheading removes dying tissue that might become a substrate for a pathogenic fungus or bacterium; getting rid of this tissue is good garden hygiene. Second, if you want to keep the flowers coming (as in the case of the petunia), then preventing any flowers from setting seed might help make that happen. In many annuals and some perennials, the plant uses a cascade of chemicals to signal the onset of maturity, or senescence, after fertilization has been successfully completed and seeds have formed.
There are plenty of other signals that will turn on the maturation and senescence processes, but in plants like old-line petunias, the longer you keep seeds and fruits from developing, the longer you can keep the plants growing and forming new flowers. You can even combine the practices of deadheading and pinching to keep the flowers coming and the plant looking great — up to a point. Eventually, the petunia will reach a mature state and enter senescence as its natural season wanes. This is much less the case with modern cultivars that’ve been developed specifically to short-circuit these natural processes. Deadheading is most effective as a tool to prolong flowering in herbaceous annuals because flowering perennials don’t count on seed production for survival. In reblooming woody plants, such as many roses, deadheading simply keeps the plant from expending energy on building seeds and fruit from an early bloom — the thought behind this practice is that the energy will be put to use in building root reserves and feeding subsequent waves of flowers.
Photo by Carolyn Lang
Photo by Carolyn Lang
The selective removal of shoots or branches of woody and herbaceous plants would all be considered pruning, to a point. While much of the pruning gardeners engage in is aimed at keeping plants healthy and structurally sound, it’s also useful for removing older, non-reproductive tissue in woody species, and it can be used in herbaceous species to enhance fruiting, fruit quality, and, as we’ve seen above, flowering.
Some of the best-known examples of pruning in the modern world involve the selective removal of branches from trees to open up the canopy, prevent disease, and minimize the potential for structural damage caused by weak crotches or rubbing branches. Setting aside woody perennial species, pruning is also useful to the culture of heirloom tomatoes, for example. Removing axillary shoots (sucker shoots) growing low on the main stem will help open up determinate type tomato plants (wherein the apical meristem is reproductive) — typically you would prune up to the first flowering branch. With indeterminate tomatoes (wherein the apical meristem is non-reproductive), you would prune similarly up to the second flowering branch, while leaving the first in place.
Now, back to that heirloom petunia you’ve been pinching and deadheading: It’s late in the season, and you note that the plant is looking fairly ratty. On a lark, or as an experiment, you can prune that petunia back to a single main shoot and then trim the shoot back severely. If it’s not too late in the plant’s life, you’ll have removed most of the sources of chemical signaling that ultimately will reduce or end its growth. Keep it protected, and if there are sufficient root reserves and remaining photosynthetic tissue, your once-aged petunia may begin its growth sequence all over again, sprouting new shoots that vie for apical dominance, and yielding another flush of flowering. This isn’t a failsafe technique by any means, but it’s almost always worth a try with your favorite annuals.
Plenty more could be written about the nuances of these often mentioned gardening methods. Do your own research on the particular plants you wish to prune, pinch, or deadhead. Understand what your goals are with modifying those plants. Deadheading annual flowers is no more a blossom-making magic bullet than is pruning tomatoes for higher quality fruit if you don’t already have great soil, appropriate environmental conditions, and plenty of sunshine and nutrients. Worry about meeting the fundamental needs of your garden first, and then experiment with these plant-modifying methods to see if you can coax more, better, stronger, prettier — or virtually any other adjective — flowers, vegetables, and fruits.
Hank Will has a Master of Science in plant physiology and holds a doctorate in pigment biochemistry and genetics. He currently serves as Editorial Director for Heirloom Gardener.