I call my collection of troughs a “troughery” (think fernery, stumpery, rockery). Although I have various plant beds with shrubs, perennials, minimal lawn, and such throughout the front and back gardens, I also have pavement including a driveway up to the patio and garage. It is these paved spaces that I use to stage my trougheries.
While some experts may not recommend siting troughs on pavement, citing the excessive reflected light and heat that can occur on such surfaces, I have not found this to be a problem. For one thing, my trougheries often include containerized small trees that provide some shade to the troughs below as well as being ornamental in their own right. I also find that spacing the troughs closely together minimizes the exposed pavement area and allows more troughs and plants to be accommodated. Having troughs in rectangular, square, and circular shapes allows me to compose interesting arrangements, with one trough playing off the attributes or supplementing the floral display of its neighbor. I also use simple low tables or even wood planks supported on overturned clay pots to elevate troughs and other containers above the pavement.
I do take advantage of the various sun exposures and microclimates that occur on my property. Most of the troughs are located in full sun on the colored concrete driveway apron but some shade is provided to them by a collection of containerized Japanese maples, a witch hazel, and a weeping Cercis ‘Ruby Falls’. These troughs include such sun lovers as small varieties of dianthus, campanula, sedum, delosperma, and potentilla, among many others. Individual containers of dwarf evergreens such as cryptomeria and small-scale erigeron add to the seasonal mix of plants and provide individual points of interest within the geometric arrangement of troughs.
The north side of my residence provides shade on the adjacent driveway for most of the day. Similar staging using low tables here allows planters to be elevated and better appreciated. Many of the containers in this shady locale are faux bois cast stone, emphasizing the shady, woodsy nature of its inhabitants. This area includes such planters with dwarf evergreens such as pieris and hemlocks, ferns, and a collection of dwarf hostas. Dwarf varieties of ophiopogon, lysimachia, and even woodland natives such as Mitchella repens round out the grouping in the shade.
Design
Being a practicing landscape architect for 36 years and counting, I can’t help but bring some sense of design to the individual troughs as well as their arrangement and relationship to one another. This is an important consideration for the troughs, especially in a small-scale setting, to avoid a feeling of disarray and disorder. I approach the design of each trough, which is in effect a miniature landscape, with the same design principles and visual effects I would expect to see in a larger-scale landscape. I often use woody plants to suggest a feeling of permanence to the trough as well as adding a sense of scale and larger, more vertical, attitude. Smaller, alpine-type plants supplement the larger evergreen or woody plants and are more horizontal or rounded in their shapes. I employ trailing plants such as small sedums, antennaria, and even sempervivum to provide that ever-important aspect of cascading plants over the edges of the trough. The “ground plane,” or interior, of the container need not be flat either, just like a full-scale landscape. I use rocks of various sizes to build up the topography of the troughs, situating them next to one another to act as small retaining walls. Filling in with planting medium behind the rocks allows the plants to assume a higher elevation, extending the visual topography, but also providing particularly good drainage. One caveat I heed when using stones or small rocks in a trough is to use all the same type, lest a range of rock types make the design look disjointed.
In addition to designing troughs as miniature landscapes, the collector in me enjoys assembling troughs of various species or cultivars of the same genus. The chance to view and appreciate often differing subjects assembled this way invites closer inspection and observation of their similarities and differences. Such troughs include one with a variety of draba species, another containing dwarf varieties of Picea glauca, and others of sempervivums. This satisfies my collector’s impulse, and arranging them in a single trough brings some clarity and purpose to the design. While some plant types, such as dwarf conifers, will eventually outgrow their containers, they may be grown together for a few years. Single genus troughs can look good with just those types (such as draba), but those made up of woody plants, such as the dwarf Alberta spruces, look better with some sort of ground cover plants added. Conversely, varieties of creeping thyme are brought together in a single trough, thereby creating a sort of thyme lawn in miniature. Spring flowering bulbs are also excellent specimens for a single genus trough and provide color to the troughery early in the season. I have used dwarf or rock-garden varieties of narcissus, crocus, tulips, and Fritillaria meleagris successfully in troughs. A major advantage of cultivating these geophytes in containers is the ability to move them out of the trough arrangement post-flowering to allow their foliage to mature and die down in a more inconspicuous place. The arrangement of troughs may then be tightened up or another more permanently-planted trough moved in.
Another type of designed trough planting can accentuate the shapes of alpine-type plants, what is sometimes called a bunnery, a collection of bun-shaped plants such as gypsophila, picea, and, chamaecyparis. Rounded river stones can gently emerge from the gravel ground plane to reinforce the bun idea even more.
Lastly, color-themed gardens may be translated to individual or groupings of troughs as well. Plants in a silver/blue themed collection, for example, can beautifully reinforce one another as a designed trough. As those specific colors are most often expressed in foliage, it is incredibly important to include contrasting textures and forms. Broader-leaved plants contrast with more finely-textured ones while others provide a more upright aspect in contrast to trailers cascading over the trough edges. Silvery, woolly, and glaucous-leaved plants often inhabit the same sunny, dry exposures in nature so collecting them in a trough this way not only emphasizes their color but also respects their cultural preferences. Occasional flowering in other colors only adds an intriguing, discordant note.
Cultural Practices
Most of my troughs are made of hypertufa, although I do have some that are actual stone or cast stone. I employ terracotta alpine pans and other similarly-shaped containers as well, often using these for succulent plants such as sempervivum. A simple square of screen is used to cover container holes to allow good drainage while permitting the soil mix to be retained in the container.
I use the same basic potting mix for all plant types from woody plants to perennials to succulents: one part Pro-Mix BX (a peat, vermiculite, and perlite based potting medium) to one part inorganic aggregate which is a combination of very small gravel (locally called grit), Turface MVP (fired calcined clay particles) and/or pumice. I refrain from using perlite as part of the aggregate component as I dislike the prominence of its white color in the mix and its tendency to blow away due to its light weight. The planted troughs are topped off with a layer of the same grit aggregate I use for the potting mixture. Individual particle size varies from an eighth to a quarter of an inch (3-6 mm). I prefer the more natural look of a varied color range in my gravel or grit with grays, browns, and burgundies predominating.
Living in zone 6b in central New Jersey (and getting warmer), I find that I don’t need to do anything special with the troughs over the winter, most of the time. Winter wetness can kill many alpine-type plants, so I am careful to stop watering them in the late fall and allow natural precipitation to supply the plants’ water needs. Luckily, I do have a detached, unheated garage at my disposal, so if the troughs are unusually wet because of prolonged precipitation, they can be trundled into the garage to allow them to dry out. The garage keeps an ambient temperature about 10 to 12°F (5 to 6°C) above the outdoor temperature. If the weather during the winter is forecast to go down to the single digits (below -12°C), I will put the troughs in the garage as well, just for peace of mind for their survival. The larger troughs are on rolling dollies to make their transport to the garage that much easier.
Maintenance
Being landscapes in miniature, troughs require similar maintenance activities. Weeds often seed in and need to be removed, easily done with a sharp-pointed small trowel to get to their roots while disturbing the surrounding plants as little as possible. Careful attention should be given to these “grow-ins,” however, as some of these may be desirable plants having seeded in from nearby troughs. I have found various species of lewisia, erigeron, and papaver, among others, to act this way. It is up to you to decide if these are allowed to stay or be pulled out. Topping up the gravel/grit used for soil covering after weeding or new planting presents a well-maintained, aesthetically-pleasing trough.
Some pruning of errant growth, especially on woody plants, is sometimes required to maintain proportion and scale in the trough. Dwarf varieties of chamaecyparis are notorious for showing brown foliage in their interiors as they age. Removing these portions can be both cathartic and aesthetic, allowing the specimen to look cleaner and often more miniature tree-like. Despite my best efforts, some plants die because of excessive rain or humidity during the summer or an unexpected wet, cold winter, but that allows a different plant to be used. I give the troughs a liquid feed once or twice in the spring but they are really on their own the rest of the year as to fertilizer. If foliage is looking yellow during the summer, I may apply a light application of liquid feed.
Final Thoughts
I suppose the small-scale nature of troughs (compared to an actual rock garden) along with their diminutive inhabitants is what attracted me to them in the first place, especially given my small property. In a limited area, these containers maximize horticultural experimentation and can be rewarding through all seasons of the year. A lack of expansive space is not a limiting factor in cultivating alpine-like plants in troughs and I urge anyone interested in doing so to embark upon the experience.
