Napa County Master Gardeners: Plants do not stretch, they stack
One of the simplest and most useful ideas a gardener can learn is that plants are not people.
That sounds almost too obvious to say. Yet many of our assumptions about plants come directly from our understanding of our own bodies.
We grew as children, so when we see a tree getting taller, we imagine something similar happening. We have broken bones and we have watched cuts heal, so when a branch cracks, we want to put it back together. We tend to understand other living things by comparing them to ourselves.
Plants are everywhere, and they invite investigation. If a strange plant pops up in your yard, you can immediately feel the leaves, snap a twig, smell it or dig around its roots. Plants are wonderfully available for experimentation. Children understand this instinctively. The trouble begins when familiarity starts to feel like understanding.
Early in my horticultural career, someone shared a phrase that I still often use: Plants don’t stretch; they stack.
Picture a child growing taller. Existing parts of the body lengthen. But a tree adds height in another way. At the tips of shoots and roots are regions of actively dividing cells called apical meristems. I picture a meristem almost like the nozzle of a 3D printer, continually laying down new material at the growing edge.
This is an imperfect analogy because some plant parts do stretch. Fruit expands as it ripens, and plant tissues can enlarge and thicken. A wound on an immature pumpkin may grow larger as the pumpkin develops.
Still, the notion of stacking gives you a surprisingly useful picture of how a tree constructs itself. A tree purchased at a nursery will not stretch to get taller. The trunk will need to have lower branches pruned off in order to appear longer. This “stacking” habit is why a branch that starts five feet above the ground does not slowly ride up into the sky as the tree gets taller.
Perhaps you have heard the old story about a child leaving a bicycle against a tree and returning decades later to find the bike high in the branches. It is an amusing image, and it feels believable if we imagine a tree growing the way a child does.
A tree can certainly grow around a bicycle, slowly engulfing it as new layers of tissue form. But it will never lift that bicycle into the canopy. The bike stays where it was, and the tree builds around it.
Once you start thinking about growth this way, a lot of other things in horticulture begin to make more sense. Consider what happens when a tree is injured.
I frequently see fruit trees carrying so much fruit that a limb cracks or partially shears off. The immediate human instinct is to save it. You prop it up, wrap it, tie everything together and hope the tree heals. That instinct comes perhaps from our own animal experience.
Yet trees don’t heal; they seal. A tree responds to injury through a process called compartmentalization. It establishes boundaries around damaged tissue and continues producing new tissue around the wound. Years later, new wood may completely surround the injury. The original damage remains enclosed within the tree.
Once you understand that response, pruning begins to look different. Removing a damaged limb can seem like a terrible amputation when we view the tree through the lens of our own physiology. For a tree, a well-placed pruning cut creates an injury it can more readily compartmentalize, allowing room and energy for future growth.
Because of these dramatic differences in physiology between plants and humans, we are able to preserve and multiply plants through grafting. Nearly every named fruit-tree cultivar you can buy has been grafted. A grower takes living tissue from one tree and attaches it to compatible rootstock. The tissues connect, water and nutrients move through the graft union, and the scion continues to produce branches and leaves.
Growth from below the graft, known as sucker growth, is undesirable. Those shoots carry the genetics of the rootstock and can become extremely vigorous if allowed to remain.
Learning plant physiology is much more useful than simply memorizing gardening tips.
We live in an age of endless horticultural advice. You can scroll online for 10 seconds and find 100 tips for a healthier plant, but if you don’t understand plant physiology, it can be difficult to know which tips are legitimate. If you take the time to learn basic physiology, the garden becomes much more readable.
Plants are strange organisms. That is part of what makes them so interesting. Understanding their physiology gives us a chance to see them on their own terms. Once you understand why a plant does something, you start asking better questions, and better questions tend to make better gardeners.
Become a Master Gardener: Join a group of enthusiastic local gardeners and become a UC Master Gardener of Napa County. Intimidated? No need! UC Master Gardeners do not know the answer to every gardening question, but they know how to find the answers. Register now to attend an information session about applying for the 2027 class. You must attend an information session to receive an application.
Fall Faire: Join UC Master Gardeners of Napa County on Saturday, Sept. 26, from 1 to 4 p.m. for the annual Fall Faire, an engaging afternoon featuring fun and informational booths staffed by Master Gardeners and community partners. Hands-on demonstrations and talks range from improving your soil health to designing a pollinator-friendly garden, along with plenty of friendly gardening advice. Shop for ornamental plants and winter vegetables, with proceeds supporting Master Gardener programs. Enjoy food from Annie’s Lunch Box food truck and live music from the Big Ranch Rounders. The event is free and no registration is necessary.
Help Desk: The Master Gardener Help Desk is available to answer your garden questions. Use our online Plant Problem Help Form or email us at [email protected]. Include your name, address, phone number and a brief description of the problem. You can also visit us in person on Mondays and Fridays from 10 a.m. until 1 p.m. at the UC Cooperative Extension Office, 1710 Soscol Ave., Suite 4, Napa.
