Glossary

Below is a list of terms and concepts often used in landscaping, site design, and related fields. This list will be updated on an ongoing basis:

Aggregate

A material formed from a loosely-compacted mass of fragments or particles, usually stone or gravel.

Altitude

The angle of the sun in the vertical plane, also thought of as how “high in the sky” it is relative to one’s location. The higher the altitude, the more direct the sunlight will be, and the shorter the shadows which will be cast on the site.

Angle of Repose

The steepest angle or slope at which a particular loose material will remain stable.

Asphalt/Bituminous Concrete

A mixture of dark pitch/tar (also known as bitumen) with sand and/or gravel. Commonly used for paving pathways, roads, and parking areas.

Axis

An imaginary straight line connecting two reference points in a design, often used as a central organizing feature with other parts or elements connected to it.

Azimuth

The angle of the sun in the horizontal plane. This is useful when determining whether a particular location on the site will likely be in sunlight or shade.

Balled & Burlapped

A common plant harvesting method used at nurseries, whereby the specimen is dug from the ground along with the surrounding soil and contained in a burlap sack. It will likely also be supported by a wire cage for protection of the root ball and as an easy handhold for transporting the specimen.

Bare Root Method

A method of transplanting nursery stock whereby a tree’s entire root structure is removed from the ground intact, dipped in hydrogel to retain moisture, and bagged. Trees are then transported to their destination and installed, ideally within 1 week of dipping.

Bitumen

The oil-based pitch or tar used as a binder for asphalt/bituminous concrete pavement.

Bollard

A short, vertical site element, typically post-shaped and no more than 4’ tall, commonly used to separate vehicle and pedestrian traffic. Bollard designs range from the simple and utilitarian to the very ornate with premium finishes.

Bond Breaker

Similar to a contraction/control joint, a bond breaker is used to create a designed weakness where a paved surface is secured to a concrete base slab with a rigid connection, such as mortar or grout. The bond breaker material itself is usually a strip of construction felt, which allows cracking to travel directly from an expansion joint in the concrete base slab to a joint between the surface pavement (usually a modular unit, such as concrete unit pavers or stone). This is done to prevent stone or unit pavement at the surface from cracking in an unsightly place, such as in the middle of a stone or paver, directing them instead to the mortar joints where they are more seldom noticed.

Caliper

A measurement of tree trunk diameter, usually measured in inches (or metric units outside the United States).

When identifying what size tree to plant, designers will typically specify a range of acceptable sizes, since nursery stock may vary.

Cation Exchange Capacity:

A measure of a soil’s ability to hold exchangeable cations, or positively-charged ions. A soil’s cation exchange capacity influences its ability to retain essential nutrients and is a strong indicator of soil fertility. It can also provide a buffer against soil acidification.

Central Leader

An ornamental characteristic describing the presence or absence of a primary stem or tree trunk. A strong or clearly-defined central leader is often considered a desirable trait when selecting certain trees at a nursery or garden center.

Clay

Fine-grained natural rock or soil particles, typically yellow, reddish, or bluish-gray, which have a particle size of <0.002mm. More plastic than silt due to its water content, it becomes hard and brittle when dried out. Clay particles will often form an impermeable layer in the soil profile, since the density of their small particles packing tightly together inhibits free drainage of water. Clay soils will tend to have a higher cation exchange capacity, making a moderate level of clay important for soil fertility.

Container Size

A common method for specifying the size of plant stock for purchase at a nursery or garden center. Containers are commonly sized in gallons (3-gallon, 5-gallon, etc., or sometimes #3, #5, etc.).

Contraction Joint

Also known as a “control joint”; a deliberately tooled or saw-cut weak point in a poured concrete slab designed to control where cracking occurs as a poured concrete mixture dehydrates and shrinks in volume.

Crown

The overall shape or form of the branches and leaves which make up the tree canopy.

Cultivar

Used broadly the nursery trade, it refers to a specific cultivated variety of a particular species of tree or shrub (“Culti-“ + “Var-“). Designers working with a given species of plant will often select a cultivar known for specific attributes, such as hardiness, size, or flower color. Market demand heavily influences what nurseries and garden centers choose to stock, and as a result some species of trees and shrubs are only commercially available as cultivars.

Dense-Graded

Consisting of a full range of particle sizes, in a relatively even distribution. In a dense-graded (or, “well-graded”) mix, larger and smaller particles can nest tightly together to form a mostly impermeable layer or aggregate.

Diatomaceous Earth

A naturally-occurring, soft sedimentary rock, easily crushed into powder, which is formed from the fossilized remains of microorganisms called Diatoms. Due to its low density and relatively high porosity, it is commonly used as a soil amendment to aid soil drainage.

Drip Line

The area on the ground beneath the tree canopy, named for the rain water dripping off of leaves and branches above. This area is especially important to protect during any site construction or disturbance which could harm existing tree roots.

Expansion Joint

A designed joint at the interface between two site elements, allowing for one or both of them to expand or shift without warping or breaking. Expansion joints are commonly placed between pavement and site walls, separating long runs of wall into parts to avoid cracking, and at regular intervals in large areas of poured concrete.

Exposed Aggregate

A type of pavement finish, most commonly with poured concrete, whereby finer particles are removed from the surface to reveal larger and more varied grains below. The effect creates a rougher, more textured pavement than ordinary poured concrete.

Footing

A below-ground structure, usually made of concrete and/or crushed stone aggregate, to support and anchor a site element at the surface.

Freeze/Thaw

A seasonal process in colder regions in which the ground freezes and thaws out, to a depth below grade which varies depending on the climate of a region (the “frost depth”). Since this often happens unevenly, the freeze/thaw cycle can cause pavement, soil, and other site elements to shift slightly unless they are anchored at sufficient depth to prevent this.

Frost Depth

The depth to which the ground can be expected to freeze in a particular region;this will vary significantly based on the climate. In order to prevent site elements from moving or shifting as the ground freezes and thaws out, it is important for their support footings to reach a depth where conditions are expected to remain stable year-round.

Grade

Describes the slope or pitch of a particular landform or surface. Usually expressed as either a percent (i.e. 5%) or a ratio (i.e. 4:1), it is calculated by determining the units of vertical change divided by the units of horizontal change. For instance, a 5% slope would represent a 5’ change over a 100’ length.

When expressed as a ratio, a 4:1 slope represents a 4-unit horizontal change per 1-unit vertical change. For example, a 6:1 slope is less severe than a 2:1 slope.

Gravel

A soil type consisting of loose rock fragments, typically with sizes ranging from as large as 64mm to as small as 2mm.

Haunch

A thickened profile of pavement or other material. Usually located at an edge condition for a cleaner appearance where one might otherwise see the setting bed or subgrade material revealed.

Heaving (Pavement)

A condition where a bump or localized expansion occurs in pavement, due to upward pressure or force. Common causes of pavement heaving include tree roots (often seen growing beneath concrete or asphalt sidewalks), water below grade freezing and expanding (“frost heaves”), or lateral compression causing the pavement to buckle.

Level

A tool used to determine the pitch of a surface.

Lime

A soil amendment consisting primarily of calcium carbonate (Limestone), usually in either a fine, granular powder or small pellets. Lime is often added to neutralize the pH of an acidic soil into an optimum range to support plant or turf grass growth.

Loam

A soil type characterized by

Mastic

A strong adhesive commonly used to secure modular pavement materials, such as brick or concrete unit pavers, in place.

Mortar

A mixture of lime, cement, sand, and water, used in masonry construction to bond bricks or stones together. Mortar can also contain other additives to modify its function for a specific purpose, such as with a rubberized admixture (“latex-modified”) for additional waterproofing properties.

Multi-Stem

A growth habit characterized by having multiple stems or leaders. Many species of ornamental trees can either naturally grow, or be trained to produce, multiple stems. This can be especially desirable when selecting a specimen tree as the focal point of a planting design.

Particle Size

Size of the component pieces that make up a given soil, usually fragments of rock or decaying organic matter. Soil particles are typically classified as either a gravel, sand, silt, or clay (in order from largest to smallest).

Peat Moss

A large, absorbent moss that grows in a dense habit in swamps and bogs, accumulating over time to form peat deposits. Peat moss is widely used in horticulture, especially as a lightweight soil medium for packing plants and as nutrient-rich compost.

Peds

Natural masses of soil separated from each other by voids or natural horizons of weakness, a structure which remains through cyclical wet and dry periods. These are naturally-occurring and not to be confused with soil fragments or clods, which are structural units formed at or near the surface by cultivation or freeze/thaw action.

pH

A measure of how acidic or alkaline a soil is. A soil’s pH can be affected by numerous factors, and can in turn affect whether nutrients found in the soil are bioavailable for uptake by plants. The pH of site soil is one of the primary factors in determining what plants will grow on a given site.

Polymeric Sand

A product which combines standard masonry sand with silica or other additives to create a binding agent or polymer. Polymeric sand is typically applied by sweeping a pre-made mixture into the joints between bricks or pavers, then lightly adding water to activate the binding agent. Although polymeric sand is more durable, stable, and resistant to washout and weed growth than standard sand, it does not drain water as freely as an open-joint system.

Portland Cement

Along with sand and water, one of the major ingredients in manufacturing concrete.

Rebar

Reinforcing steel commonly used to strengthen cast concrete. The name is derived from its primary purpose (“Reinforcing Bar”).

Rebar is typically classified by number (#4, #5, etc.) with the number corresponding to 1/8” increments in diameter (a #4 bar is 4/8, or 1/2”). Designers commonly specify sizes from #3 to #8, depending on the type of construction and any recommendations made by the project engineer. In addition to standard steel rebar, epoxy-coated rebar products are also common throughout the design and building trades.

Root Zone

The area beneath the surface where a tree or shrub’s primary root mass is located (not specifically referring to the roots, just the area they are in.)

Runoff

Surface water that cannot be absorbed by the land, causing it to flow across the land in response to the landform. 

Sand

A medium-sized soil particle with a size typically between 2mm and 0.05mm.

Scoring

The pattern of expansion and contraction/control joints, which is either tooled or saw-cut into poured concrete. This is typically done at between 4′ and 6′ on-center spacing, and patterns can also be modified in a decorative way, or to align with architectural features.

Setting Bed

A base layer on which a surface rests, typically a sand or gravel product. Depending on the type of surface material (stone pavers, brick, etc.), a setting bed may be designed to either promote the flow of water through the pavement profile and into the ground, or in some cases to anchor the pavement material in place.

Sight Triangle

Usually located at intersections, a sight triangle describes a setback required to see approaching motor vehicle traffic from an intersecting roadway. The name is derived from the triangular shape that is required to be kept clear (extending a given distance from the intersection on both roads, then connecting those two points).

Silt

A fine soil particle with a size typically between 0.05mm and 0.002mm.

Smart Level

A 2-foot long instrument commonly owned by contractors and design consultants for purposes of checking the pitch of paved surfaces on the site.

Soil Horizon

A layer parallel to the soil surface, whose physical characteristics differ from the layers above and beneath. Each soil type usually has three or four horizons, which are usually defined by obvious physical difference, often color and/or texture.

Soil Texture

Refers to the proportion of sand, silt, and clay particles that make up a given soil.

SWOT Analysis

Systematic analysis of a site’s Strengths, Weaknesses, Opportunities, and Threats; a useful tool when performing a site inventory/analysis at the beginning of the design process.

Variety

A slight genetic variant of a species, which can freely interbreed but is distinguished by a distinct attribute or characteristic (form, color, texture, etc.).

Welded Wire Mesh

Medium-to-heavy gauge wire which is added to poured concrete construction for reinforcement, as with rebar. Welded wire mesh is typically used in thinner concrete pours, where there might not be sufficient concrete coverage for the much thicker rebar (most design professionals will recommend a minimum of 3″ between any rebar and the surface of the concrete).

Zone (Or, USDA Hardiness Zone)

Based on a wide range of climate data, the USDA produces a keyed map of “zones” based on the range of expected minimum temperatures for that region. This is a widely-accepted industry standard in the nursery and landscape design professions, and typically trees and shrubs will be classified accordingly in nursery or garden center catalogs (“Zone 3a”, for example). When determining whether or not a plant may be suitable for a particular area, comparing its hardiness zone rating to that area’s designation on the USDA map can be helpful. This map is updated periodically.