Glossary of Common Horticultural Terms



Any substance used to assist the decomposition of organic matter in the preparation of garden compost.

Acid Soil

Having a pH below 7. The preferred soil reaction of Azaleas, Blueberries, Camellias, Chinese Magnolias and Dogwoods.


Introduction of air to compacted soil by mechanically removing plugs of topsoil. Aeration helps oxygen, water, fertilizer and organic matter to reach roots. Also, incorporating air into compost by turning the pile. Incorporating air into compost helps the plant material decompose more quickly.

Aerial Phytophthora

A highly transmissible fungal disease which will devastate Madagascar Periwinkle (vinca) if they are planted before mid-May, receive less than full sun and are given overhead watering.


Requiring available oxygen to live. For example, composting is performed by aerobic organisms; but rotting occurs under anaerobic conditions.


Applied agricultural science dealing with rural economy and husbandry. In recent years it has concentrated mainly in the theory and practice of crop production and soil management.

Alkaline Soil

Having a pH above 7. The characteristic reaction of soils derived from limestone. In such soils, elements like iron and zinc are not readily available to



A genus of fungi containing plant pathogens. Causes the following: Citrus Fruit Black Rot, Early Blight of Potato or Tomato, Gray Leaf Spot on Cabbage, Poinsettia Blight, Tomato Stem Canker, etc.


Requiring the absence of oxygen to live.


A plant that germinates, grows, flowers, produces seed and dies in the course of a single growing season.


A disease caused by the fungus Colletotrichum, not Gloeosporium as stated by some. it is characterized by sunken, dark lesions or spots in leaves. May be observed in: Ash, Elm, Mulberry, Red Oak, etc.

Apical Dominance

The chemicals produced by a growing shoot tip which restrict the growth of lower, dormant buds, keeping them from growing.




A usually unicellular, prokaryotic organism without a nucleus. Some cause diseases of plants.


An area of raw soil that is usually planted with flowers or vegetables. Also known as flower beds.


A fast-spreading fungal or bacterial disease which causes dead patches on stems or leaves and can kill the whole plant.

Blossom End Rot

In tomatoes, not a rot, but a dying back of the distal (farthest from stem) end of the fruit. Occurs when there is insufficient soluble calcium in the soil and inconsistent watering.


Usually features decorative plants or garden accessories such as bricks and gravel which are located alongside another landscape feature such as a fence or patio.


A genus of fungi containing plant pathogens.


A true bulb is thought to be a complete or nearly complete miniature of a plant that is enclosed in fleshy leaves called scales, which contain a provision of reserve food. If you were to cut a Hyacinth bulb in half (bud to root) it is most interesting to see that the flower is housed there, waiting to emerge into our world. Wrapped around a bulb is a thin outside covering called a tunic. These are like flakey leaves. The basil plate which is located at the base of the bulb holds the food storing scales together, and new roots will sprout from the outside edge of the basil plate once the bulb ends its dormant period and begins its growth cycle. Daffodils, Hyacinth, Lily, Tulips and Onions are what are called True Bulbs.




A sunken lesion caused by the breakdown of tissues from the phloem and outward.


The chilling hours a particular clone needs before over-wintering buds will open.


The green matter in plants and the essential molecule for photosynthesis.


A foliar symptom of a mineral deficiency, stress or disease; the absence of chlorophyll. Inter-veinal chlorosis (the veins remain darker than the remainder of the leaf blade) usually indicates a lack of iron.


Humus made by decomposing vegetative matter in a compost bin or pile.


It is a signed document that outlines the work to be performed by the installer and a schedule of payments to be made by the customer, and the circumstances under which the work will be done and payments will be made.


Usually the first seedling leaf to appear when a seed germinates. Some flowers, such as lilies will only produce one leaf, while most others will produce two.


The transfer of pollen from one plant variety to another.


The part of a plant where the roots and stem meet, usually at soil level.

Crown Gall

A grotesquely-enlarged, abnormal body on the stem of a plant near the soil surface. Usually caused by a bacterial infection.


A cultivated variety of plant, often bred for a desired trait, such as pest or disease resistance, flower colour, fruit color and/or persistence, habit/size, foliage colour/texture, etc.


A plant propagation method wherein a part of a plant is cut and dipped in a rooting hormone to eventually grow into a new plant.



Damping Off

Death of a seedling by rot occurring when there is inadequate light and ventilation, as well as too much water and a pathogen.


To remove old flowers to prevent seedpods from forming.


Alive but in a state of suspended animation until all conditions are right for growth.

Downy Mildew

A fungal disease of plants characterized by visible, off-white spore masses on the leaf underside.


The movement of water through the soil. With good drainage, water disappears from a planting hole in less than a few hours. If water remains standing overnight, drainage is poor.

Drip Irrigation

This is the practice of applying water slowly through various types of pipes, tubes or specialized hoses. The simplest form would be the use of soaker hoses commonly found in garden centers. More sophisticated systems can be installed by homeowners or irrigation contractors that are preset to go on by a computer.



Early Blight

The progressive yellowing and dying of the leaves from the ground up. In tomato, caused by Alternaria solani. Etiolation – The abnormal elongation of shoots under low fight levels.


A shallow trench or physical barrier of metal, wood, brick or synthetic material used to define the border between lawn turf and another area, such as paving or a flower bed.


Fungi that live in some grasses (called endophytic) and make them harmful or deadly to a variety of above ground grass-eating insects.


The bacterium, is the causal agent of Fireblight, Historically, it was the first plant disease identified as being caused by a bacterium.


The intensity, duration and variation in sun, wind and temperature that characterize any particular lawn or planting site.




One group used in classifying organisms. Families consist of a number of similar genera (plural for genus).


A product containing one, two or all three plant macronutrients (nitrogen, phosphorus and/or potassium).


The Rose Family disease caused by Erwinia amylovora, marked by the progressive blackening and dying of shoot tips and leaves, which can kill the whole plant.

Full Shade

A site that receives no direct sun during the growing season.

Full Sun

A site that receives at least eight hours of direct sun each day during the growing season.


Plural of fungus.


Something which kills fungi. Most of these products, however, do not kill the spores.


A kingdom of eukaryotic (see prokaryote), non-photosynthetic, organisms. They are not a part of the plant kingdom. Some cause diseases of plants.


A genus of plant pathogenic fungi; some are saprophytes. Fusarium oxysporum, which causes wilts, has numerous forms and affects many economically important plants.




A group of species of plants that are closely related


The beginning of growth in a seed; to sprout.


The degree and direction of slope on an area of ground.

Graft Incompatibility

The eventual failure of the graft union, due to pathogens or physiologic reasons, usually causing the death of the scion (part being propagated).

Ground Cover

A plant, such as ivy, vinca or juniper, used to cover the soil and form a continuous low mass of foliage. Often used as a substitute for turf grass, especially in shade, embankments, or other areas where turf grasses don’t perform well or are difficult to maintain. (Can also mean material used to cover the ground and prevent weeds from reaching the surface).



Harden/Hardening Out

A method used to climatize seedlings and plants that have been started indoors to be transplanted outdoors. Place the plants in a sheltered, sunny place, outside, for a few hours at a time and return them to the house, greenhouse or garage each night. Extending the outside time each day until the risk of frost has passed and the plant can be moved to a permanent outside location. Use of a cold frame can help to speed up the process if the growing season is short.


A plant’s ability to survive the winter without protection from the cold. The temperature range in which a plant will grow and thrive. Cold is usually the main consideration; however, heat and humidity can also cause plants to fail.


The installation of non-plant features in the landscape. These include features such as: walls, walks, driveways, kerbs, patios, etc.


A plant with soft upper growth rather than woody growth that is found in shrubs. Annuals, bennials and perennials may be herbaceous.


A plant killer. Herbicide injury on non-targeted plants can mimic certain diseases.


Someone who has extensive knowledge of plants, their care and their requirements for survival.


Thoroughly decayed organic matter. Added to lawns gardens or beds, it will increase a soil’s water-holding capacity, improve aeration and support beneficial microbial life in the soil.


A crossbred cultivar that is not likely to breed true from seeds. Some methods of propagations such as division or cutting should produce identical copies of a hybred parent.




Absolutely not susceptible to a disease.


The largest group of arthropods. They can damage or kill plants directly or indirectly, as disease vectors.


Something which kills insects.


This is the practice of applying supplemental water to plant and lawn areas.




This is ‘the lay of the land’ which includes plants and other physical features such as lawn or meadow areas, waterways, pavement, utilities, structures, etc. Mistakenly used to refer only to planting in many instances.

Landscape Architect/Designer

A person who has education and/or training in the design of residential and commercial properties. Jobs can include plantings, walkways, walls, water features, landscape lighting, fences, and other similar features. LDs are often employed by a design-build firm that does most the work themselves. They may contract some tasks to other companies. They may have a Landscape Architecture degree from an accredited college.

Landscape Contractor

A firm that implements landscape plans prepared by Landscape Architects or Landscape Designers. They may bid on a job or work with the designer throughout the design process. Depending on their in-house expertise, they may hire sub-contractors to perform specialized tasks such as masonry, paving, carpentry, etc.

Landscape Fabric

A synthetic fabric that is usually water-permeable, it is spread under paths or mulch to serve as a weed barrier.

Lawn Restoration

Improving a lawn by a combination of fertilization, aeration, turf plug planting, and/or seeding without killing or removing all existing turf.


A form of propogation in which shoots that are still attached to the mother plant are layed on top or just under the soil surface so that rooting occurs. Once rooted, the layered section can be cut from the mother plant and moved elsewhere. Strawberry plants are good candidates for layering.


Generally, a localized site of damaged or diseased plant tissue. Can be caused by bacteria, fungi, viruses or be environmental in origin (freeze injury, mechanical abrasion, sun scald, etc.)


A white or grayish mineral compound used to reduce soil acidity and to supply calcium for plant growth.


An ideal soil type for growing, loam contains an equal balance of sand, silt and clay. It has benefits of both clay and sand in that it will hold moisture and organic compounds, yet it is porous and will drain well.




A visible fungal growth on the exterior of a plant.


A small arachnid; usually found in large numbers sucking sap on leaf undersides. Mite infestations are sometimes confused with diseases.


Something which kills mites.


Well-defined, generally angular, discolored zones on leaves. One symptom of a viral infection.


A layer of bark, peat moss, compost, shredded leaves, hay or straw, lawn clippings, gravel, paper, plastic or other material spread over the soil around the base of plants. During the growing season, mulch can help retard evaporation, inhibit weeds and moderate soil temperature.




Something which kills nematodes.


Tiny, wormlike animals which can penetrate roots and cause galls (abnormal swelling of plant tissue) and other malformationsNutrient – One of the elements required by a plant for its growth.


A joint in plants from which leaves emerge.


Nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron and other elements needed by growing plants and supplied by minerals and organic matter in soil and by fertilizers.




In horticulture or agriculture, systems in which no chemicals or pesticides or fertilizers are used. Acceptable organic growth methods include natural plant derived or mineral substances along with the acceptance that certain pest and diseases be allowed in the garden.

Organic Matter

Plant and animal residues, such as leaves, trimmings and manure, in various stages of decomposition.


Plants grown for aesthetics, not consumption or economic use.


Spreading seed over established turf that has been prepared for restoration.




An organism on or in another one, deriving some or all of its nourishment from its host.


A disease-causing organism.


A plant that lives more than two years or three seasons and normally flowers annually. Many die down during the winter but the roots are unaffected by frost and new growth appears as the weather improves and the temperature rises.


Synthetic substances used to kill and assortment of pests that might include weeds and insects. Herbicides, fungicidess and insecticides are all types of pesticides.


The light-mediated reaction in green plants where water and carbon dioxide become carbohydrates and oxygen.


The “potency of Hydrogen”. A number from 0 to 14, the negative logarithm of the Hydrogen ion concentration of a solution. A pH of 7 is neutral. A reading below 7 is acidic, one higher than 7 is alkaline.


A very large and quite variable fungal genus containing plant pathogens.


A plug plant is any developing plant whose growth cycle is initiated well in advance of its actual planting. Plug plants are designed to be introduced to your garden or landscape with substantial growth already established. Once assimilated the plant can begin to produce flowers, fruit or vegetables much sooner than traditional seed planting.


The transfer of pollen from the stamen (male part of the flower) to the pistil (female part of the flower), which results in the formation of a seed.


Using pruning shears to remove or cut back the branches of woody plants.


The most important member of the group, Pseudomonas syringae -It causes Bacterial Stem Canker in stone fruits and dozens of other diseases.


A genus of fungi, closely related to Phytophthora, which contains plant pathogens. Causes blights, rots and damping off.




The proposed price to perform the work outlined on an accompanying plan or document. Also referred to as a bid.



Raised Bed

An elevated garden bed offering better drainage, aeration and warmer soil than a conventional bed.


Able to suppress a parasite, pathogen or pest by chemical or mechanical means.

Retaining Wall

A wall built to stabilize a slope and keep soil from sliding or eroding downhill.


A fungal group containing plant pathogens. Rhizoctonia solani is the causal agent of Brown Patch in ‘Raleigh’ St. Augustinegrass.

Rosette Disease

A zinc deficiency of pecans growing in alkaline soils. Shoot tips do not elongate normally and the leaves are crowded together, almost like a rosette.


A plant disease caused by a fungus and named because of the orange, orange-red to rusty color of the spores.




A plant or fungus which draws nutrients from dead organic matter.


A lesion characterized by a thickening and malformation of the outermost layers of plant tissue.


A young plant grown from seed.


Plants that do not require pollen from another plant to produce fruit.


A plant disease caused by a fungus), visible as a body of very dark spores.


A small, hard reproductive or resting phase of a fungus, bacterium, fern, etc.


The practice of driving a support into the ground next to a plant to support it in its growth.


The male reproductive organ of a flower, consisting of a filament and a pollen-containing anther.




A layer of undecomposed stems and roots near the soil surface which can harbor pathogens and block the flow of water into the root zone.


Able to live in the presence of a disease or pest and not be affected.

Trace Elements

Elements required by plants for their mineral nutrition in smaller quantities than either the macronutrients or micronutrients.


To remove plants from one place and replant them in another (or from a container into the ground).


Latticework used to support climbing plants .

Trickle Irrigation

This is the practice of applying water slowly through various types of pipes, tubes or specialized hoses. The simplest form would be the use of soaker hoses commonly found in garden centers. More sophisticated systems can be installed by homeowners or irrigation contractors that are preset to go on by a computer.


Are rough skinned and produce roots from many parts of its surface. New plants come to life from eyes or growth buds from this short, fat, bumpy exterior. Anemone, Aladium, Gloxinia and Tuberous Begonia all belong to the tuber family. To reproduce, Begonias grow larger and produce growth buds while Caladium grow new tubers from the sides of the original. Ranunculus and Dahlia are just a few that are part of the Tuberous Root family and in fact are truly real roots. Their food supply is kept in the root tissue and like tubers, they produce buds from which new plants grow. The growing area is often called the crown and the buds are restricted to the neck of the root where they grow on the base of the old stem.




An organism which transmits an infectious agent.

Veinal Necrosis

A symptom of Oak Wilt in Live Oaks. The interior portions of the leaf are discolored, yellow to reddish-brown, while the margins remain green.


A lightweight, flaky mineral called “mica” that has been heated to the point of expansion. The sponge-like granules are then capable of holding both water and air. This amendment is added to potting mixtures and container gardens to improve root growth due to aeration and moisture retention.


A genus of fungi containing plant pathogens. They generally invade vascular tissues and cause wilt diseases.


Nucleic acid surrounded by a protein envelope. It can reproduce only within a host, usually with disastrous consequences.




Soil that is saturated with water.


Any undesirable plant or grass species; any plant growing where you don’t want it.

Wilt Disease

A loss of turgor (water pressure) in shoot tips or leaves caused by a pathogen interfering with vascular tissues.

Witch’s Broom

A crowded mass of abnormal branching and rebranching; usually pathological, sometimes propagated as a novelty.