Any plant problem or disorder that is not caused by living organisms (such as insects, fungus, or bacteria) is considered abiotic. Examples of abiotic disorders include drought stress, sunscald, freeze damage, wind injury, nutrient deficiency, overwatering, or chemical injury from fertilizers.
Soil that is alkaline has a high pH (between 7.0 and 14.0 on the pH scale). Alkaline soil tends to have more of certain micronutrients, including calcium, sodium, and magnesium. Most clay-heavy soils are alkaline. Alkalinity in water is a measure of the buffering capacity (the ability to resist a change in pH), not simply the amount of hydrogen ions present (which is how pH is measured).
Learn more: Soil pH for Fruit Trees: Why It Matters and How to Adjust It
An aril is a fleshy covering that surrounds the seeds of some plants. In the case of pomegranates, the aril is the juicy, bright-colored, edible part of the fruit. The white flesh of lychee and the dried covering surrounding a nutmeg kernel (where the spice mace is derived) are other edible examples of arils.
A tree that has been dug up and stored without any soil around its roots is a bare-root tree. Trees ordered online are often bare-root, and they may cost less than potted saplings. Bare-root trees must be planted quickly in order to avoid their roots drying out.
In gardening, a berm is essentially a strategically placed mound of dirt. Berms are often used as design elements in order to highlight a focal point, elevate a planting bed, create a sense of direction for foot traffic, or serve as a privacy screen.
A small berm, a few inches high, may be constructed in a ring about 18 inches from the trunk of a newly planted tree. This type of berm serves as a basin to catch rainwater (or manual watering). The captured water can then soak into the ground more slowly without running off (as it would if the ground were flat around the tree).
Biennial (alternate bearing)
Biennial-bearing fruit trees produce a heavy crop every other year, with a lighter or nonexistent crop in between. Many fruits are prone to biennial bearing, including mango, citrus, figs, persimmons, avocado, stone fruits, apples, and pears. Regular pruning and fruit thinning can help biennial trees produce a consistent crop every year.
Some fruiting vines, such as blackberries and raspberries, produce fruit on biennial canes. The fruit only grows on 2-year-old floricanes, after which the cane dies back. Each year the plant produces new canes, called primocanes, which will become the following year’s fruiting floricanes.
A Bordeaux mixture is a combination of copper sulfate, hydrated lime, and water which is used to prevent fungal and bacterial infections in fruit and nut trees and other ornamental plants. A common ratio of the active ingredients is 1/10 of a pound each of copper sulfate and lime to 1 gallon of water. For specific instructions on how to prepare a Bordeaux mixture, visit this site.
The term bramble refers to a tangled, thorny shrub, typically in the Rubus genus (including blackberries, raspberries, dewberries, and boysenberries). Most brambles have crowns that are perennial and produce biennial fruiting canes. Brambles are often considered invasive, especially outside of their native range.
Also called the branch shoulder or callus roll. This is the swollen or bulbous-looking area at a branch base where it meets the main branch or trunk. It may look like wrinkled or folded bark, or simply like a wider part of the branch.
When making pruning cuts, it’s important to cut a branch at a slight angle above the branch collar. The collar is there to protect the tree and ensure that wounds heal properly. If you cut into the callus, the cut may not heal and disease or decay could be a result.
In fruit, Brix is the measure of soluble solids in the juice of the fruit, including sugars, acids, vitamins, minerals, and other compounds. Brix is used commercially as an indicator of the sweetness or ripeness of certain fruits, such as wine grapes, citrus, pineapple, and berries. Brix is not the only measure of fruit quality, as other factors (acidity, texture, other flavor compounds) can affect a fruit’s taste.
Bud break happens when new green growth starts emerging from a tree’s buds, and it is the first indication that a tree is awakening from dormancy. New shoots or blossoms will then sprout from the buds. Bud break is an important marker for the timing of certain garden chores, such as pruning and the spraying of fungicides.
The whitish tissue sometimes surrounding the pit cavity of a peach or nectarine is called callus tissue. It may look like white dots or residue on the pit or around the cavity. Callus tissue is made up of a group of undifferentiated cells (essentially cells that aren’t fully developed into peach flesh). It’s naturally occurring and perfectly safe to eat.
The outermost layer of a blossom is called the calyx. A calyx is made up of sepals, the firm, leaf-like shapes at the base of a flower. A calyx (plural calyces) protects a blossom before it opens, and supports the inner structures of the flower once it unfurls. The calyx is still present on some fully mature fruits – notably persimmons (the calyx is the leathery, leaf-like whorl at the stem end) and pomegranates (the calyx becomes the spiked crown-shaped organ at the blossom end away from the stem).
Trees with a central leader form have one main trunk (leader) with scaffold branches growing off of it. They tend to be conical, or wider at the base and narrower at the top (like a Christmas tree). Apple, pear, and sweet cherry trees prefer a central leader structure.
The average number of hours spent between 32° and 45°F each winter (minus any hours spent over 60°F) are an area’s chill hours. The hours do not have to be consecutive; the chill hour total accumulates over the whole dormant season. Most fruit and nut trees need a certain number of chill hours in order to bloom and produce fruit.
Chlorosis occurs when normally green leaves turn yellow (iron chlorosis appears as yellow leaves with deep green veins). This yellowing can be caused by a number of factors, including poor drainage, incorrect soil pH, nutrient deficiency, drought, or root injury. Chlorosis is a symptom of these problems, and can be corrected by treating the source of the issue.
Related: Soil pH for Fruit Trees: What It Is and How to Adjust It
Clay is one of the three types of particles that make up soil (the others are silt and sand). Clay particles are the smallest, only 0.002 millimeters or less, and they tend to be flat or plate-shaped. Because of their size and shape, the clay particles easily compact together to form a solid mass. Clay also feels sticky when wet.
Clay is an important component of healthy, loam soil, because it helps to retain moisture and provide structure. However, soil with too high a percentage of clay will have trouble draining and may cause problems for the roots of fruit trees and plants.
Cross pollination occurs when pollen is transferred from the male flowers of one plant to the female flowers of another. Many fruit trees, including most apples, pears, cherries, and many stone fruits, need to be cross-pollinated with another variety of the same type in order to produce fruit. Trees that do not need cross-pollination are considered self-fertile. Even self-fertile fruit trees will have an improved crop if there is another variety nearby to help with cross pollination.
Learn about apricot pollination here: All About Apricot Pollination: One Tree or Two?
Learn about persimmon pollination here: Persimmon Tree Pollination: Do You Need Two Trees?
A crotch angle is the angle between a branch and the trunk of a tree. For fruit trees, it’s best to have crotch angles greater than 45°. Narrow crotch angles can weaken a tree and break more easily under a heavy fruit load.
Trees that are deciduous lose their leaves every winter. The opposite of deciduous is evergreen, where trees keep their leaves year-round. Many fruit and nut trees are deciduous, including peaches, figs, pears, plums, apricots, cherries, persimmons, pecans, and walnuts. Examples of evergreen fruit trees are avocado, citrus, feijoa, papaya, and olive.
With dioecious fruit trees, male and female flowers grow on separate trees. In order for dioecious trees to be pollinated, both a male tree and a female tree must be present. Common dioecious fruit trees include persimmon, kiwi, and pistachio.
Deciduous trees, including most fruit trees, survive the winter by going into dormancy, where their energy consumption and growth processes slow down. Just like some mammals hibernate in the winter, trees go dormant to protect themselves from the cold and to conserve resources until the growing season begins again.
The dripline of a tree is located directly under the outer circumference of the tree’s canopy. This dripline is also known as the critical root zone (CRZ) or root protection zone (RPZ). It’s best to water or fertilize a tree near the dripline, rather than close to the trunk. The terminal ends of a tree’s roots contain smaller feeder roots that absorb nutrients and water from the soil. If you water too close to the trunk the tree won’t absorb it as well, and it could cause root rot.
A drip line could also refer to a small emitter hose used for drip irrigation. Drip line irrigation allows water to slowly seep into the soil near a plant’s roots, minimizing water waste and evaporation.
A drupelet is one of the small subdivisions (that look like little spheres) that make up a fruit such as a blackberry or raspberry. In a blackberry, for example, each individual drupelet contains its own seed, so it is actually a collection of many drupes clumped together. A drupe is a fleshy fruit that contains a single seed, like a cherry, peach, or olive.
An espalier (eh-SPAH-lee-ay) is a tree that is trained to grow flat against a wall, fence, or freestanding trellis. Espalier allows fruit trees to bear fruit prolifically in a small area. The tree stays more compact, making harvest easier, and the branches are pruned to maximize sunlight. Apple and pear trees are the easiest to espalier, but you can also use figs, stone fruit, citrus, pomegranate, or persimmon.
Learn more about espalier here: Espalier Fruit for Beginners: 10 Things to Know Before You Start
Learn how to set up an apple espalier here: Starting an Espalier Apple Tree: A Step-By-Step Guide
Extension service (agricultural, county, or cooperative extension service)
An extension service is a group of local experts that provide free, informal gardening and agricultural information to farmers and local gardeners. These services originated in 1914 when the U.S. Department of Agriculture partnered with universities across the country to provide better resources for farmers. Today there are many extension services in every state that hold events, offer lectures and courses, and answer questions. Visit this site to find a list of extension services by state.
Fig latex is the white, sticky sap that appears when leaves or unripe figs are removed from the tree. Once a fig is fully ripe, it will not ooze white sap from the cut stem. Fig latex can irritate the skin, and can cause an upset stomach if too much is ingested. Research is being done into the effect of fig latex on the growth of gastrointestinal cancer cells.
Learn about when figs are ready to be picked here: Picking Perfect Figs: How to Tell When Figs are Ripe
A floricane is a stem of a plant that must grow for a year before it can produce flowers or fruit. Raspberries and blackberries, for example, only grow fruit on 2-year-old floricanes. A new cane that will not fruit in the current season is called a primocane. Floricanes are usually woodier and darker than primocanes and will produce blossoms and fruit in the current season.
Spraying fertilizers (or other water-soluble products such as neem oil or kaolin clay) directly onto the leaves of a plant is known as foliar feeding or foliar spraying. The direct contact with the leaves allows nutrients to quickly be absorbed into the vascular system of the plant, showing results in as little as a day or two.
When foliar feeding, always spray in the early morning or in the evening when there is no direct sunlight, to avoid burning the leaves. Use a more diluted concentration of the liquid fertilizer since it is contacting the plant directly, rather than being absorbed by the roots.
A graft union (also called a graft collar) is the raised, lumpy area on a plant’s trunk where the scion has been attached to the rootstock. There may be a slight deformity on the trunk at the graft union, but it does not affect the health of the tree. Shoots that grow from below the graft union, if allowed to continue to grow, will have characteristics of the rootstock plant only.
In pruning, a heading cut is used to influence the growth of the tree. The end of a branch is removed at an angle with a pruning saw or shears, which encourages new shoots to grow. This kind of cut strengthens branches, causes new branches to grow from below the cut, and helps control the size of the tree.
Heat units (also called growing degree days [GDD], effective heat units, or growth units) are used in agriculture to estimate crop development during the growing season. Essentially, it’s the difference between the average daily temperature and the minimum temperature at which growth will take place for that plant.
Horticultural oils (also called dormant oils) are refined, oil-based products used to prevent and treat pest infestations on fruit trees and other plants. They work by essentially suffocating the insects or disrupting their metabolic processes. These oil sprays can also serve as a good eco-friendly fungicide to prevent and treat powdery mildew, rust, and sooty mold. Most (if not all) horticultural oils are safe for organic gardening.
Although horticultural oil products are technically broad-spectrum pesticides, meaning they can be harmful to any insects, they have a short residual effect. The excess oil evaporates quickly, so it is active as a pesticide for only a short time. They are often used while trees are dormant, to avoid harming pollinators or other beneficial insects.
Loam is soil that contains relatively equal amounts of sand, silt, and clay, which allows the soil to retain moisture while still draining well. Loamy soils hold nutrients better than sandy soils, and they drain better than heavy clay soil. Loam is generally considered ideal for most garden plants, although some plants do prefer lean, sandy, rocky, or wet soil.
Macronutrients are the elements plants need in relatively large amounts for growth and development. The three primary macronutrients are nitrogen, phosphorus, and potassium (the “NPK” numbers on a fertilizer package). The secondary macronutrients are calcium, magnesium, and sulfur.
Manual pollination (hand pollination)
Manual pollination is the process of hand-transferring pollen from the male stamen of one flower to the female pistil (stigma) of another flower. This is typically done with a small paintbrush, cotton swab, or other soft implement. Hand pollination is helpful if the weather conditions are not friendly to pollinators (cold, wet, or windy), or when a plant is having trouble setting fruit.
Micronutrients are elements present in soil that plants need in trace amounts (much less than the macronutrients). The name “micronutrients” does not mean that these elements are any less important to plant development, but that they are simply needed in very small amounts. The main micronutrients are nickel, iron, zinc, copper, boron, manganese, molybdenum, and chlorine.
A microclimate is a localized area with different atmospheric conditions than those nearby. One relatively small space, such as a backyard, may have several microclimates. For example, the top of a small hill may receive more wind but less frost than surrounding areas. A space near a wall or fence may reflect the sun’s heat and warm up sooner in the spring. Microclimates are useful when planting fruits that are borderline hardy in your zone.
Nutrients are considered mobile if a plant can move them from one part of the plant to another. It can be helpful to know which nutrients are mobile in a plant in order to diagnose nutrient deficiencies. For example, nitrogen, potassium, and magnesium are mobile, so deficiencies of these minerals will show up in older leaves first (because the plant will “rob” the old leaves to develop new growth). Iron deficiencies, and other immobile nutrients such as zinc, will show first on new young leaves.
Modified central leader
With the modified central leader form, the main trunk (leader) is shortened and allowed to branch into secondary leaders. These trees have a rounder shape than with the central leader form. Persimmons, figs, pomegranates, and many nut trees are often pruned to a modified central leader shape.
The three numbers featured on a fertilizer package (such as 12-12-12) are called the N-P-K ratio. These numbers indicate the percentage by volume of each of the three elements, nitrogen (N), phosphorus (P), and potassium (K). For example, a 6-2-4 fertilizer would contain 6% nitrogen, 2% phosphorus, and 4% potassium. How low or high the numbers are show how concentrated the formula is. Organic fertilizers tend to have lower N-P-K ratios than synthetic fertilizers. A 4-4-4 fertilizer would have the same proportion of N-P-K as a 16-16-16, but would be only a quarter as concentrated.
Trees pruned into an open center form have a vase-like shape, where the scaffold branches reach outward and the middle of the tree is left open. This structure maximizes light and airflow throughout the tree. Most stone fruit, including peaches, plums, nectarines, apricots, sour cherries, prefer an open center form.
Organic matter in soil is made up of things that were once living. This could include all types of plant and animal tissue in various stages of decomposition. Most fertile soil contains between 3-6% organic matter.
Organic matter serves some important functions. It enhances water retention, improves soil structure and aeration, and provides nutrients that are broken down by microorganisms in the soil and made available to plant roots. Just about any soil can be improved by adding organic material.
Fruit species or cultivars that produce fruit without viable seeds (or that are seedless) are parthenocarpic. This occurs when fruit develops without fertilization. Examples of parthenocarpic fruit are bananas, pineapples, figs, pears, and some persimmons.
A perennial plant is one that lives for two or more growing seasons. Most fruit and nut trees, vines, and bushes are perennials and can grow fruit year after year. The opposite of perennial is annual, meaning a plant that lives only one season.
Photosynthesis is the process plants use to convert sunlight, carbon dioxide, and water into food. Plants then store this food and use it for growth, cell development, and seed production. Chlorophyll (the green pigment in plant leaves) traps light from the sun, which is then synthesized into carbohydrates the plant can store and consume. Plants release oxygen into the air as a byproduct of photosynthesis.
In fruit plants, the process of photosynthesis can affect fruit quality. This is why most fruit trees, shrubs, and vines need to be planted in full (at least 6-8 hours per day) sun. Pruning to open up the plant can also increase sun exposure, especially for the leaves and branches near developing fruit.
Persimmons are pollination-variant (PV) when the flesh changes color and quality after pollination. The pollinated PV persimmon has seeds and darker brown flesh, whereas the same cultivar is lighter and seedless when unpollinated. ‘Chocolate’ (Diospyros kaki) is an example of a pollination-variant persimmon cultivar.
Persimmons are pollination-constant (PC) when the flesh has the same color and quality when pollinated or unpollinated. A PC persimmon that has been pollinated may have seeds, but the color and flavor of the fruit remain the same. ‘Fuyu’ (Diospyros kaki) is an example of a pollination-constant persimmon cultivar.
A pollinizer is a plant that provides pollen. Many fruit trees, such as apples, pears, sweet cherries, and plums, need to be pollinated to grow fruit. The source of this pollen is another tree, the pollinizer. (This is different from a pollinator, which is the agent that transfers the pollen, such as a bee or the wind.)
A primocane is a new cane (long, stem-like growth) that will flower and fruit the following year. A primocane is identified by its vigorous growth, bright green color, and lack of blossoms. The current year’s primocanes will become the next year’s floricanes, which will then produce fruit (as with blackberries and raspberries)
(Also called red drupelet reversion, red cell regression, red drupelet disorder, or red cell.) Reversion occurs when previously black-colored blackberries turn partially red. Reversion is caused by sudden temperature changes, damage during harvest, or an excess of nitrogen at harvest time. Cell damage causes the anthocyanin pigment (which makes blackberries black) to degrade, changing the color.
Rootstock is the base of a plant, including the roots and part of the trunk or stem, onto which another plant is grafted. Rootstock is used to give the grafted plant or tree more desirable traits, such as cold hardiness, disease resistance, size, productivity, or longevity. Fruit trees grafted onto rootstock tend to produce fruit much sooner than those grown from seed. The top part of a plant that is grafted onto rootstock is called a scion, and the two plants are joined at the graft union.
Scaffold branches are the main structural branches of a tree. The scaffolds are the large branches attached to the main trunk (or trunks). Lateral branches are those that grow off of the scaffolds. Fruit trees often grow best if only a few scaffold branches are selected while the tree is young, and the rest are removed.
A scion is the part of a plant that is joined onto rootstock. It will form the top part of a grafted plant or tree, and will eventually grow into the plant’s branches, leaves, blossoms, and fruit. The type of fruit that’s produced is determined by the scion. For example, a scion from a ‘Jonagold’ apple tree will still grow a ‘Jonagold’ apple, no matter what rootstock it is combined with. The grafted tree will have some characteristics from the rootstock, such as size, cold hardiness, or disease resistance, but the fruit comes from the scion.
Fruit trees that are self-fruitful can be pollinated from flowers on the same tree. In some cases, pollen can be transferred to the stigma of the same flower. The opposite of self-pollination is cross-pollination.
Self-fruitful plants are valuable to home growers with limited space since only one tree or plant is needed for fruiting. In many cases, however, cross-pollination may produce larger, better, and more abundant harvests, even in self-fruitful plants.
Silt is one of the three types of materials that make up soil (the others are clay and sand). It has moderate-sized particles between the size of clay and sand. Soils high in silt tend to be very fertile, somewhat well-drained, but still able to retain moisture. Silt has a powdery feeling when dry and doesn’t clump together like clay does when wet.
Soil pH is a measure of how acidic or basic the soil is. It is indicated on a logarithmic scale of 0.0 to 14.0, where 7.0 is neutral, less than 7.0 is acidic, and more than 7.0 is basic. Every plant will grow best within a particular pH range. Most fruit trees and plants will do well in soil with a pH between 6.0 and 6.8, because most nutrients are soluble in this range. Proper soil pH is necessary in order for a plant’s roots to absorb the nutrients it needs to grow and fruit.
Learn more: Soil pH for Fruit Trees: Why It Matters and How to Adjust It
Sooty mold is a fungus that grows on plants covered in honeydew, a sticky substance left behind by aphids, mealybugs, leafhoppers, whiteflies, and other insects. The fungus looks like a fine layer of black, powdery soot. Sooty mold doesn’t actually infect plants, but it can block light from reaching the leaf surface, prohibiting photosynthesis and stunting the plant’s growth.
Controlling sooty mold starts by combatting the insects that produced the honeydew. Controlling the ant population nearby can also help, as ants use honeydew as a food source and therefore protect the honeydew-producing insects. The mold itself can be washed off the plant surface with a stream of water or a mild soap and water solution.
Split pit/pit splitting
Pit splitting is where the stone (or pit) in the center of a ripened fruit is not whole, but is instead cracked, split, or even shattered into pieces when the fruit is cut open. It often happens due to excessive watering, fertilizing, or over-thinning stone fruit.
Spur-bearing fruit trees grow fruit on short, woody shoots (spurs). These spurs will typically bear fruit for several years. Apples, pears, pomegranates, cherry, and plum trees are often spur-bearing, depending on the variety.
Spur-bearing apple trees tend to grow slower, stay more compact, and produce more fruit buds per branch than tip-bearing trees. Spur-bearing trees are best for espaliers and trellis systems because they grow more fruit per branch.
Subtropical climates are characterized by hot and humid summers, like in tropical climates, but with cool to mild winters. They are typically found on the southeastern part of each continent between 25° and 40° latitude. Subtropical climates are adjacent to tropical climates in the direction away from the equator (toward the poles).
More on climate types from The National Weather Service: https://www.weather.gov/jetstream/climates
Sunscald (or southwest injury) is an injury to young, thin-barked trees caused by damage to cells under the bark surface. In winter, the cells warm up during the day and become active, then are damaged by the harsher cold at night. In summer, sunscald is caused by extreme heat and sun exposure. Sunscald often happens on the south side of the plant, as that is where the sun hits most throughout the year.
In pruning, a thinning cut is used made to remove unwanted shoots and open the canopy to increase airflow and light. A branch is removed right at its point of origin (just above the branch collar), which won’t signal the tree to grow another branch.
Tip-bearing apple trees (also called non spur-bearing or terminal-bearing) grow fruit in clusters at the very ends of long shoots from the previous year. Tip bearing trees tend to have a weeping form, due to the weight of the fruit at the branch ends. There are far more spur-bearing apple varieties than tip-bearing. Partial tip-bearing apples grow fruit both on spurs and at the terminal ends of branches.
An area’s water table is essentially the level underground at which the soil is always saturated with water. Groundwater fills in all of the air holes below the water table, but open pore spaces exist in the soil above the water table (aeration zone). If your water table is too high, it could cause drainage problems for your fruit trees. The water table fluctuates somewhat throughout the year.
A whip is a young tree seedling with a slender central leader and no side branches. Whips are typically under 3 feet tall (about 1 meter) and between 1/2- and 1-inch thick. Many specialty nurseries sell fruit trees as whips, as they can grow more varieties and ship them more easily. Planting a whip gives the gardener more control over the shape of the plant as it grows.
A windbreak is a barrier – either natural or artificial – that serves to block or slow strong winds in a garden or other agricultural area. They are often made up of two or three dense lines of trees, shrubs, or other plants that reach a sufficient height (at least 2.5 feet) to be effective. Windbreaks have many benefits, including reducing wind erosion (soil erosion due to high winds), creating microclimates, controlling snow drifts, preventing pest issues, and improving irrigation efficiency.
Read more about the purpose and design of windbreaks here.