Updated: Oct 5, 2021
To take the mystery out of how landscape architects classify ornamental plants for their use in designs, I thought it would help to explore the terminology that is commonly used. This list will be revised and expanded as time allows, but the intent is to provide such list to my students, or anyone interested in working with designers, as it may help in communicating interests.
Accent & Specimen Plants
The best definition I found to date comes from the Extension Foundation:
Accent plants can be used to draw attention to a particular feature or features in the landscape such as an entryway, stairs, water, seating, statuary or even other plants. They should contrast with the surrounding plants or other elements to create emphasis or focal points.
Specimen plants, a form of accent plant, are individual plants that are used singly to show off some special feature of the plant such as flowering display.
To achieve accent status, designers will consider such characteristics as color, texture, and form that will stand out from the adjacent plantings. For specimens, their "special features" will be based on plant characteristics as well; its contrast to other species, however, could be more significant, such as a lone tree with striking bark set within a winter dormant landscape. Or in the case of this example at West Valley College, a flourishing Aesculus californica set within a drought-stricken planting area.
A formal tree lined walk, but the trees could also be topiaries, pollarded, or pleached (see below). Designers have used this form for everything from estate driveways with grand oak trees or eucalypts to small garden paths flanked with flowering crabapples, as the photo below illustrates from the Elizabeth F. Gamble Garden in Palo Alto. Note the boxwood hedge boarding the vinca and bulb beds.
In each situation, trees are equally spaced for defining an overall effect, such as contrasting light and dark, open versus enclosed, or a frame for a distant focal point, such as the small fountain on one end of the axis and the sundial at the other, shown below.
Below is a lickety split run through an Allée.
The term barrier for the landscape industry applies to many situations and materials, so it might be best to start with its most basic definition: something material that blocks or is intended to block passage (Merriam-Webster). For landscapes, barriers could mean maintaining the separation of materials, such as weed fabric that prevents weeds from taking hold, or filter fabric, allowing water to penetrate while keeping clean gravel separated from soil, are such examples. Root barriers prevent (or intend to prevent...I have reservations) roots from creeping into areas such as under sidewalks. When we discuss plants as barriers, designers intend to prevent people or animals from traversing between spaces, similar to how bollards might be used yet not fitting the "hostile landscape" designation.
Barrier plants fall into at least two categories: 1) plants with thorns, such as blackberry brambles (shown above), which are indeed quite hostile if you try to penetrate their border, or 2) dense plants that would need a machete to pass, such as a highly dense bamboo stand (shown below). In both cases, plants are used to control the movement of people by preventing cut throughs or trespassing and redirect people around plants-based obstacles.
Beds, Bedding Plants, Flower Beds
While it is entertaining to see how many people have posted their old iron bedframes used in their gardens, and bedding plants are used for such scenarios, this use is not what was exclusively intended by landscape professionals. The idea of setting plants in beds has been around for ages, but its American forms came into vogue in the 17th & 18th centuries, following European examples. Bedding plants refers to small-scale, prolifically blooming plants, usually annuals, grown in various high-volume containers such as 6-packs and flats. They are used in dedicated flower beds intended for display, which commonly have themes, such as a vegetable bed, cut-flower bed, seasonal color bed, bulb bed, etc. Other plants, such as perennials and shrubs can certainly be used as well...purest might disagree, so they are more often used in borders.
Beds are lined with some type of edging to distinguish the bed from adjacent areas, such as paths or lawn. Edging may assist in raising bed elevations as well; bricks or stone allow for amending the soil, and raised areas provide positive drainage. Boxwood hedges or other tightly clipped evergreens are traditionally favored to form bed perimeters; a series of decorative beds lined with boxwood may also be defined as a parterre. Today, designers are not limited to traditional types of edging and may opt for commercial grade materials like steel, coupled with new plant introductions or irregular bed shapes. Two of the following photos are from early family vacations and look a little grainy, but you get the idea. I am not sure what Stanford is attempting here...a redwood tree perhaps?
In the truest sense of the word, we need to first look at their origins in early French and English gardens. I reference The Oxford Companion to the Garden (Oxford), describing the border garden beginnings with plate-bande in 17th century France. Google translates plate-bande as a flower bed, but the literal translation noted in the Oxford reference is 'flat strip.' Counter to being flat, the topography rose and fell in undulating mounds to allow some plants as featured objects. Some plate-bande designs were round, providing opportunities to plant tall species in the center and graduate them down to short species along the outer edge. If not round, these early borders were straight, long, and with varying depths; all had the goal of display, to feature familiar and unusual collections with a focus on complimentary colors, forms, and textures.
English designers expanded upon plate-bande concepts to what we know today as the English perennial border, made famous by John Claudius Loudon and ultimately by Gertrude Jekyll (perennial border by Jekyll shown below). Perennial borders continued to highlight colors, forms, and textures using herbaceous perennials, which were splendid for one or several seasons but then go completely dormant in winter. Today's clients, however, are interested in dynamic borders that have interest all year round, especially here in California's fair weather.
Today, designers may blend herbaceous perennial borders with annuals and shrubs to extend seasonal interests. I consider American landscape architects like James Van Sweden and partner Wolfgang Oehme, who introduced the use of perennial grasses, allowing them to linger through winter dormancy, to inspire borders with unusual off season texture value. I hear designers refer to conifer borders and shrub borders that adopt the idea of specific collections. When we identify plants for use in borders, they have been found worthy of such displays.
Bosque, Bosco, Bosquet
To get to the modern use of bosque, we start with a few historic references. Bosco, Italian for wood, takes on special significance in garden design. Once again, we turn to Oxford referencing 15th century Hypnerotomachia Poliphili that illustrated garden elements designers still use today, and in this case represented journeys through a forest, to put it simply. In landscape designs of the subsequent Renaissance period, the bosco became more refined, intentional, as a setting for meanderings highlighted with sculpture, buildings, and storytelling. One surviving example is Sacro Bosco (photo below).
From here we can travel to France for a refined interpretation known as a bosquet. Remembering the Italian meaning for bosco mentioned above, boschetto is a "small wood or clump of trees" (Oxford, p. 55), so it is easy to understand the French bosquet has a similar meaning. We are shifting to baroque gardens now, furthering the aesthetics of these small woodlands with formally set trees on a grid pattern, much like we understand orchards today, except these historic gardens were primarily ornamental not utilitarian. Everything was formal about bosquets, from the trees, possibly clipped to geometric shapes to the pathways and any ornamentation. As a side, bosquets also implemented another design consideration, of dark vs. light, void vs. mass, by have a central clearing that might include a specimen tree, water feature, or art.
From these period reference designers use the Spanish bosque, or at least this was the term we used in the days of my landscape architecture apprenticeships. Their formal layout would be in line with the French bosquet, such as Dan Kiley's and Peter Ker Walker's modern interpretation at Fountain Place in Dallas, Texas. Which leads me to ask, can a formal stand of bamboo be defined as a bosque, as in this example I captured on the Stanford campus?
Oxford takes us through an eloquent history of container gardening, so no need to reiterate here. For our purposes, plants associated with container gardening are most often but not always small. Think annuals, perennials, cacti, succulents, vegetables, etc., but we can also consider bonsai, specimen shrubs and small-statured trees. Yes, large trees can be in containers; I enjoy sharing a story about a landscape contractor moving a full-sized oak in a 24' wood container set on the platform used for moving the former Space Shuttle, just so it could be relocated a quarter mile out of the path of a new road corridor. This is an example of a temporary situation. Containers here means plants that can remain in their pots for their lifespan. Note the situations where long-term care, including root pruning, is necessary, such as bonsai gardening, greenhouse citrus, or vines. For the latter, I discourage most vines in pots; their vigorous growth can become a maintenance nuisance.
Full admission, this category is contentious for me. Not as a landscape typology but the frequency of its failure. Simply stated, foundation plantings are species that lend themselves to locations along the base of a structure, or foundation, that at times includes unattractive elements that need to be hidden, such as vents, pipes, and the foundation itself. The Spruce writes a more detailed description of three types of foundation plantings: entryways, corners, and "bridge the gaps" between the former two. This is a good place to start, but there are a few other considerations.
Over the years, I have met architects (and landscape architects) that do not appreciate foundation plantings because they cover up their designs. They are right to protest, for clever design does not need covering up and should be accentuated instead. Foundation plantings are merited when design has not met such criteria; we often resolve to "shrub it up" to hide unattractive elements.
The other challenge, and this happens often, occurs when designers, property owners, and landscapers fail to consider the conditions and plant heights at maturity. Here are two examples: 1) Planting shrubs that cover windows and other desirable elements as they mature, and 2) Planting shrubs or small trees too close to the structure that conflict with eaves and soffits over time. One such plant is Dicksonia antarctica, a tree fern, which I often have seen planted too close to buildings. Homeowners (and some designers) forget how tall they become. Of course, the hint is in the common name...again, tree fern...reaching 15' tall when mature. As they grow, they conflict with any overhangs including eaves and may look out of place, contorted, and needing removal. Designers should be making an evaluative call, assessing mature heights and widths of plants and trees to avoid such problems down the road.
I have one photo I recently took in Palo Alto that exemplifies the idea of layering. I am sure I can drum up a few more, but lets start here. In fact, I will include additional terminology also depicted in this photo. Overall, the plantings act as a border along the sidewalk. Certainly, the owner desires their privacy, so we have a screen here as well. For layering, we have foreground (daylilies), middle ground, currently as an accent (roses and Japanese anemones), and two layers of background in the from of a hedge (English laurel) and what appears to be a tree line of maples, although with my eyes I am not so sure.
In this context, one landscape use is commonly called out when describing plants and their function: background. For larger species, such as privet or in this English laurel example, we identify their value for background planting. Their presence at the back of a border helps to accentuate any smaller plants in the foreground. Their form could be informal or formal, but either way designers are looking for darker, evergreen plants, although deciduous shrubs can play a part as well if the overall composition requires such contrast.
Mass & Ground Cover
Plants of all kinds are designed into landscapes for certain effects: single plants may be used as an accent or specimen, while a few of the same plants can be used in small groupings or in mass, planted together to visually read as one unit, such as these succulents in the Stanford Quad. Ground covers are mass plantings, but not all mass plantings are considered ground covers. I argue that ground covers are plant species that grow wider than tall, whereas plants used in masses can grow more upright, tightly planted together. For our purposes here, I present this photo below of junipers used in mass to create a larger ground cover.
To be clear, ground covers are not limited to lawns or ivy. The junipers at Stanford are woody coniferous shrubs. Vines, like honeysuckle, bougainvillea, or star jasmine, allowed to trail along the ground, would be categorized as a ground cover in this context. There are numerous plants that expand by use of stem runners or rhizomes with different performance values, forming dense carpets or loose patches but still valued for their ground cover use.
Hedge (Formal vs. Informal) & Screen
Hedges perform critical functions in landscape designs, where they quite literally express an architectural form outdoors: walls. Successful walls will define one space from another, an easy task for interior spaces, but there are several considerations when creating walls with plants. Evergreen or deciduous? Informal or formal? How tall, and based on that information, what species or plant type to specify, annual, perennial, vine, shrub, tree, ornamental grass? What will the hedge look like when first installed versus at maturity? Will it need to be replaced someday, and if so, when and what is the succession plan?
Evergreen hedges function most directly as walls with a sense of permanence and their ability to articulate space. Deciduous hedges, however, provide an opportunity for spaces to change with the seasons, and thereby alter the visual experience from restrictive to filtered views through and to spaces beyond, allowing light to penetrate within. Remember this when specifying a screen, which serves two purposes: to create privacy and/or to hide undesirable elements. If using deciduous materials, that screen might fail its intended purpose.
Formal versus informal should be determined during the design process, then specify the appropriate species to achieve the task. Here are a few tips:
Formal hedges are best derived from species with small leaves and dense structures, simply because trimming is less noticeable, and they lend themselves to sharper corners and other shapes.
Specifying large leaf species for formal hedges should be relegated to large hedges where scale of leaf to mass makes sheared and mutilated leaves less noticeable. Trees can make large hedges, too, so their leaf size might not be a significant concern when viewing from a distance.
Consider the rate of growth. Slow growing species, such as Buxus sempervirens 'Suffruticosa,' do not need a high frequency of pruning, whereas vines (yes, vines can be used as hedges) might need frequent pruning throughout growing seasons, meaning high maintenance.
Informal hedges open the palette of plants to wider diversity of textures, forms, and colors. Camellia sasanquas, the floppy, arching cultivars, are good examples of what to use as an informal hedge. Their mounding habit is difficult to restrict, so let's say it in song, "Let it go, let it gooooo!" Restricting the form of many flowering species may also means a loss of flowers that would have bloomed on new growth or terminal stems. Other plant types that lend themselves to informal hedges are ornamental grasses (note any seasonal dormancies), including bamboo.
Screens are essentially hedges that restrict the view both inward and outward. A screen, however, never obligates to any shape, form, or specific species. In fact, a screen can be made from a collection of plants by mixing trees and shrubs into one mass of varying heights and depths. Just remember if using deciduous plants that the screen may not be as effective over the winter.
This is a contentious subject, I will confess. While there are a number of trees conducive to planting within lawns, designers and homeowners tend not to install them correctly leading to future problems. Set aside understanding how tree grow and develop shade, lawns can suffer as trees mature. What was once in full sun will deteriorate in shade, which is different criteria needing shade-loving grass. But let's focus on the tree, planted in lawn, and what that means in California.
When we add trees to lawns in our Mediterranean climate, we forget why they may do so well in other regions of the country. The Midwest and East Coast receive regular amounts of summer water without irrigation (there are exceptions, of course). Soils remain moist, therefore tree roots can penetrate deep into soils. By contrast, lawn trees in California are unable to find deeper water, coupled with compacted soil, tending to keep their roots close to the surface. This is where other problems come into play: competition between roots and lawn (usually the tree wins), surface roots become tripping hazards, and if close to sidewalks, can uplift concrete. If the soil is poorly draining, then trees can become compromised with age, vulnerable to root rot.
For California, the best solution is to keep lawn away from the trees, mulch the tree's rooting area, and provide separate irrigation that will water deeply and infrequently, even in the summer. We are in a drought now and probably for awhile. Look around you. Have people shut the water off on their lawns? How do the lawn trees look? If they are not on a separate irrigation system, they will struggle and even die for lack of water. Remember, lawn trees in our state tend to be shallow rooted, failing to probe deep where moisture might still be available.
Pleaching, Pollarding, and Espalier
These are fun modifications intended to use plants in very creative and architectural ways. Pleached and espaliered trees or shrubs are pruned to limit their three dimensional value, often creating formal structures such as fans or strong horizontal branching. Viewing such plants from their face, they can appear to be fully formed structures, but turn to the side and their structures are exceedingly narrow. Pleaching is uncommon in the United States, but it is an effective means of delineating limited space and formality with trees. A metal frame is constructed to train the trees to appear freestanding, whereas espaliers tend to be mounted on a wall or fence. Vines, shrubs and trees are used as espaliers and are also helpful in restricted spaces. Nurseries will sell espaliered fruit trees, shrubs like camellias or gardenias, and vines like star jasmine so buyers can get a head start. I have espaliered a Meyer lemon around the pool equipment to soften the wood fence.
Unlike pleached or espaliered plants, pollarded trees retain their three dimensional value but with a twist, or in this case, a lot of pruning. Each year, gardeners will remove branches to a certain spot on primary branching, leaving what some call a knuckle. These blunt limbs become highly sculptural and formalize the trees in a very stylistic way. In spring, new leaves and limbs will protrude from these knuckles, and in summer, look like a highly structured green umbrellas. One of the most common trees for pollarding is the London plane, or Platanus x hispanica. They can be seen in Golden Gate Park across from the California Academy of Sciences or at San Francisco's City Hall.
All three do require considerable maintenance and commitment from the project owner, often requiring specialized gardeners and arborists to do the jobs. If left unattended, plants and trees will do their best to revert to their natural forms. Unfortunately, this usually means malformed and weak limbs that are vulnerable to breakage, so designers should consider this long-term investment.
Shade, Shade Tree, Understory:
These categories are almost self-explanatory, because people will seek the shade of trees when the sun shines bright. For landscape designers, shade trees become architectural elements, designed as outdoor protection and ceilings. Trees will scale. There are grand, large specimens that produce large shady areas if they are broad in form. Narrow but tall trees, not so much, but both can act as overstory to smaller trees that become an understory. Layering canopies in this way creates interesting vaults, dimension, and texture along with diversifying a woodland. An understory can be further enhanced with smaller shrubs, perennials, and ground covers.
Topiary & Bonsai:
I debated if this category should be included with other manipulations such as formal hedges or espaliers, but they really deserve their own category. Topiaries are formed through pruning and training trees, shrubs or vines into any shape imaginable. I cannot remember which English country estate exactly, but while touring a topiary allée with my fellow classmates we encountered a ten foot plus topiary phallus. We never did get an explanation. Topiaries are often planted in the ground and formed over time with dedication, but they can also be planted in containers, which is why I included bonsais here.
Bonsai are highly articulated trees dwarfed by the restrictions of containers and ongoing limb and root pruning. Readers will see in TELCS' plant lists a few noted for their bonsai qualities, such as lace leaf Japanese Maples. Books are dedicated to bonsai history, care, and collections, and designers might specify a bonsai in their designs. Again, lots of dedicated maintenance, so choose wisely.
Incidentally, large plants and trees can be bonsai'd...I just made the word up, but talking with others we frequently use the term as a verb. Bonsai'd trees and shrubs are not true bonsais but find themselves in restricted rooting space, and over time will require either removal or root pruning. A couple examples are the trending balcony planters on high rises we see today, or proprietary tree well filters used for stormwater capture. In both situations as a municipal plan reviewer, I see that designers are not considering long-term management of trees in restricted spaces, not to mention limb and fruit drop from high above...but that's another story.
Accent planting at mountain: "Azalea Valley in Mifuneyama Garden and Mount Mifuneyama 3" by そらみみ is licensed under Creative CommonsAttribution-Share Alike 4.0 International.
Barrier to pasture: "Sheep, bales, bramble hedge, Caerlesi Common, Trelech - geograph.org.uk - 970316" by Dylan Moore is licensed under Creative Commons License.
Bamboo with path: "Through the Bamboo Garden" by Shubhika Bharathwaj is licensed under Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0).
Jekyll garden: "The garden designed in 1908 by Gertrude Jekyll at the Manor House in Upton Grey, Hampshire" by Anguskirk is licensed under Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0).
Herbaceous perennial border: "English Herbaceous Borders | Waterperry Gardens, Oxfordshire, England | ( 3 of 50)" by ukgardenphotos is licensed under Creative Commons -NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0).
Lincoln Center Bosque: "The Trees of Lincoln Center Bosque at Night: New York City, New York 2009" by DeepRoot is licensed under Creative Commons NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0).
Schönbrunn bosquet: "42 Apollo in bosquet Fächer, gardens of Schönbrunn 03" by Herzi Pinki is licensed under Creative CommonsAttribution-Share Alike 4.0 International.
Golden Gate Park bandshell: "Golden Gate Park - San Francisco, California" by Doug Kerr is licensed under Creative Commons Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0).
Pleached swag: "Just one of the tremendous avenues of pleached lime trees, the longest in the U.K., at Amport House in Hampshire" by Anguskirk is licensed under Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0).
Pleached fencing: "Pleached Fencing, Wreningham - geograph.org.uk - 352057" by Ian Robertson is licensed under Creative CommonsAttribution-Share Alike 2.0 Generic.
Pleached trees, hedge, and lawn: "An immaculate avenue of pleached trees and yew hedging at Dipley Mill in Hampshire" by Anguskirk is licensed under Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0).
Garden tunnel: "Hampton Court Garden Tunnel - geograph.org.uk - 1800549" by william is licensed under Creative CommonsAttribution-Share Alike 2.0 Generic.
Shade garden: "A place to relax, backyard garden, patio table and chairs, potted plants, trees, Lake Forest Park neighborhood, Seattle, Washington, USA" by Wonderlane is licensed under Creative Commons Attribution 2.0 Generic (CC BY 2.0).
Container photos by TELCS.
Foundation photos by TELCS.
Hedge photos by TELCS.
Topiary and Bonsai photos by TELCS.
Garden tunnel without frame by TELCS.
Photos with captions by TELCS.