The Life of a Fruit Tree
By Orin Martin
The end of dormancy is signaled by terminal bud swell, just before the buds burst open, pictured here on the branch of an apricot tree. Photo by Adobe Stock/Piotr
For the past 40 years, I’ve been teaching people how to grow fruit trees organically at the University of California, Santa Cruz (UCSC) Farm and Alan Chadwick Garden. The garden spans about 3 acres, perched on an impossibly steep, south-facing slope on California’s Central Coast, and has been a teaching garden since 1967, when Chadwick, a pioneer of organic French intensive gardening, began it as an experimental teaching garden at the newly founded university. In a sense, he was the Rosetta stone for all that’s unfolded subsequently in the field. His gardens, and those he inspired, exemplify a confluence of technique, science, art, and aesthetics. As organic gardeners, we owe him an extreme debt of gratitude.
For four decades, I’ve been that old guy leaning on a spade, expounding on the merits of cover crops and compost to a group of idealistic, hardworking apprentices. In addition to the apprenticeship program, we sell vegetables, flowers, and fruit through a community-supported agriculture (CSA) program, a market cart, and to the cafeterias at UCSC. We also distribute free produce to food pantries on campus, helping to combat food insecurity among students.
Photo by Getty Images/cotuvokne
The program has graduated more than 1,500 apprentices who’ve gone on to found and lead organic farms, teaching gardens, and food justice projects around the country and throughout the world. My own fruit tree addiction started with apples. The apprentices tease me that, after 40 years in the orchard, I still haven’t gotten out of the “A” section of the fruit tree catalog. But why would I need to? One of the advantages of apple trees is that, thanks to an array of size-controlling rootstocks, they lend themselves to intensive plantings and small gardens. But after 10 years of specializing exclusively in apples — with more than 120 cultivars at last count — the Alan Chadwick Garden orchard is now graced by a collection of stone fruits, including apricots, peaches, nectarines, plums, and apriums and pluots, the later two of which are both apricot-plum hybrids. The truth is, all fruits are great.
A Paradise for Every Generation
The people of this planet have a long and storied association with trees. Put simply, the story of fruit trees is the story of us. Some archaeobotanists argue that fig orchards once dotted the eastern rim of the Mediterranean Sea and eastward toward the upper Euphrates River Valley. These early orchards may have predated the wild progenitors of wheat, barley, oats, emmer, and other ancient grains that propelled humankind into farming some 10,000 years ago. Since then, we’ve benefitted from the presence of trees in the immediate landscape and, more fundamentally and simply, trees on the planet.
Photo by Getty Images/nikamata
Of course, people grow fruit trees for a variety of reasons — for fruit, shade, aesthetic beauty, and perhaps, with a bit of nostalgia for our primate pasts, climbing and swinging through them. Whatever your reason, it’s heartening to remember that the act of tending to an organic orchard — whether it’s one little peach tree or an entire acre of apples — can also be a chance to turn back the clock on some of the damage humans have done to the earth. Along with enhancing biodiversity in any garden, planting trees can aid in saving the planet; trees sequester atmospheric carbon, essentially modifying the environment and cooling it. When we garden, we should keep in mind that we’re very much growing fruit trees in order to grow more trees. Like soil stewardship, fruit tree culture is intergenerational; we’re growing fruit trees for the next generation, and for subsequent generations, too.
Taking Root: The Grand Period of Growth
Spring is the most dynamic time of the year in the orchard. Much of what fruit trees do annually is compressed into a narrow window from the spring equinox to just past the summer solstice. This time of year sees maximum root and shoot growth, followed by flowering, fruit set, and “sizing,” or fruit enlargement, in addition to the beginnings of next year’s fruit buds. Pomologists of the late 19th and early 20th centuries often referred to the tumult activities compressed into this specific short period of intense growth as the “grand period of growth.” This is when syncopation really gets going: Roots, flowers, fruits, leaves, and shoots are actively growing and exhausting the tree’s stored reserves, while the next year’s flowers and fruit buds are getting started inside the tree’s growing branches.
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There’s a considerable lag between a tree’s spring growth needs and the uptake of nutrients from the soil, as well as the production of carbohydrates from the leaves. So the roots, with their carbohydrate and nutrient reserves, act like a sourdough starter in spring and early summer by kick-starting the annual cycle of tree growth.
Fruit trees have radial root systems that are somewhat asymmetrical. With the exception of a taproot, which serves primarily to anchor the tree, most of a fruit tree’s roots are shallow, superficial, and fibrous or branching. They generally extend out to or beyond the drip line — the imaginary circle around the circumference of the tree canopy where rain or irrigation water drips off the leaves and onto the ground. The first wave of root growth occurs a few weeks prior to any visible bud swell, leaf, or shoot growth, as roots can grow at cooler soil temperatures than the aerial portions of the tree. The roots of fruit trees start growing in temperatures of 40 to 45 degrees Fahrenheit, as compared with most vegetable and flower crops, which make little or no growth with soil temperatures below 55 degrees.
Photo by Getty Images/Oleksandr Bushko
In early spring, roots become active to fuel the aerial components of the tree. The curve of growth is essentially straight up, peaking in mid-spring and tapering off by the summer solstice or shortly thereafter. The word “surge” would be an apropos description of this first wave. Toward the end of spring, root growth slows down and shoot growth reaches its peak. In a slow, relentless manner, the fruits are enlarging, as the harvest approaches.
A Surge of Fruit
With stone fruits, especially apricots and peaches, the initial rate of fruit sizing is impressive, even alarming. You might think you’ve gone through the looking glass with Alice, or you’ve fallen into the pages of James and the Giant Peach. But usually after 6 to 8 weeks, sizing virtually stops. At this juncture, the pit with its embryo is enlarging and hardening. After this lag period, fruits continue growing in size and increasing in weight until harvest. With apples and pears, sizing is more consistent, slower, and steadier.
Photo by Getty Images/Anna Pismenskova
In midsummer, fruit takes over and garners the lion’s share of a tree’s resources. Root growth slows down, shoot growth subsides, and carbohydrates have been depleted. This ebb is the reason W. H. Chandler, a senior statesman of American horticulturalists, whose 1951 book Deciduous Orchards is still considered an authoritative tome on the topic, coined the term “dormancy of summer” to describe the estival quiescence of fruit trees. In these hot months, as much as 70 percent of a tree’s annual carbohydrate reserve goes into fruit production. More than any and all activities in fruit trees, fruit production is a huge nutrient sink. You could even say fruit is like a corporate robber baron, grabbing a disproportionate percentage of the available resources. It’s your job to play Robin Hood. You can redistribute the wealth with adequate fertilization in spring and summer, and by beginning your cover crops in late summer.
Photo by Carolyn Lagatuta
Approaching the autumnal equinox, there’s a second significant, if less explosive, wave of root growth. Then root growth slows again and reaches a yearly low as the tree loses its leaves and enters dormancy. This is an important time in the cycle to attend to watering and weed control.
In fall, the trees are ablaze with color one moment, and then bare and exposing their lovely architecture the next. They drop their leaves, but their roots continue to grow at a slow rate, storing carbohydrates and nutrients for spring growth. As the days grow shorter and temperatures drop, dormancy proceeds apace. Dormancy is an adaptive feature of deciduous trees to prevent cold injury and death to tender buds and leaves. While it begins in mid to late summer with the cessation of branch growth, it accelerates well before the obvious leaf drop of autumn. Shorter days — with fewer than 12 hours of daylight — and temperatures below 45 degrees, increase the rate of dormancy. The colder it is, the quicker leaf drop happens. But the word “dormancy” itself is a misnomer. Although trees appear dormant in winter, and the cessation of growth and the shedding of both fruit and leaves occurs, there’s still some metabolic activity even in the dead of winter.
Dormancy begins when fruit trees produce a terminal bud (in this case, a small red pear fruit) to prevent shoot extension, signaling the tree to store nutrients instead. Photo by Getty Images/sony_moon
The first visible sign of the long descent into dormancy is the cessation of shoot extension in midsummer. Terminal bud set on the ends of branches heralds this change. This tip bud is pronounced and swollen; with pome fruits, it’s often a fruit bud. At this point, the tree will no longer make further extension growth, even if aggressively watered and fertilized. Instead, it’ll absorb nutrients, translocate carbohydrates, and store them in the trunk, inner bark, and roots for quick mobilization during the following year’s “grand period of growth.”
Before the leaves drop, they pull nutrients, especially nitrogen, back into the tree. Around this time, trees also develop bud scales — tough, leaf-like appendages that envelop and protect buds from cold injury. Think of them as bud blankets. The buds appear to swell and take on a fuzzy, gray hue.
Photo by Getty Images/Elliott Bignell
Bud scales produce a plant hormone called abscisic acid (ABA). During early dormancy, ABA accumulates in bud scales and moves down the branches by gravity. The accumulation of ABA in buds keeps them from breaking dormancy during false spring thaws, thus providing an evolutionary safety net. This hormone also sends a message to the tree (as anthropomorphic as it sounds): Don’t grow yet! Rest! Wait for spring!
In winter, the trees seem dormant, but in reality, they’re only quiescent. There’s no apparent growth, but internally, flower buds are slowly developing, with spring waiting in the wings. Roots, although hidden from view, exhibit some activity in all but the coldest climates. Over time during the winter, cold temperatures and UV sunlight degrade the ABA in the bud scales. Dormancy ends when the ABA is exhausted and no longer controls the inner workings of the tree. The tree will then break from dormancy, and when it warms up, the buds will burst anew.
Advice for Growing Miniature Fruit Trees
Follow these tips from homesteader and writer Mary Lou Shaw to enjoy miniature citrus trees that can grow in any Zone with some careful tending.