Planting Permanent Pots

Most everyone has an indoor potted plant or two. Perhaps an assortment of African violets thriving by an east-facing window over the kitchen sink or a collection of cacti and succulents basking in a hot southern exposure. Growing tender or tropical plants outside in containers is also a routine practice for gardeners.

Numerous books have been written on its art and technique. Permanently planted containers can offer display outside year-round, and will endure despite exposure to our frigid winter temperatures. There is little literature on this subject, however, and some authors even admonish against the practice. Well gardeners like nothing better than a challenge, so I’ve been successfully growing trees, shrubs and perennials year-round in permanent containers for more than twenty years.

Thriving in an entrance garden is a yew (Taxus cuspidata ‘Capitata’) that was planted in a thirty-six inch pot in 1982, and pruned into a topiary form. Thuja occidentalis ‘Rheingold’, a favorite dwarf conifer with chartreuse foliage graces our garden at home in a complementary cobalt-blue pot. A dwarf Chinese elm (Ulmus parvifolia ‘Seiju’), that looks like a bonsai even without any effort, is content in a container at Elm Bank, the Massachusetts Horticultural Society’s headquarters in Dover.

The first matter to consider is weatherproof pots. There are many materials from which to choose: rot- resistant wood, cast stone, lead and zinc, hypertufa and even durable plastics that mimic terra cotta. I am particularly fond of stoneware pots. Stoneware, even unglazed, becomes vitreous from its high firing and does not absorb water like soft, low-fired earthen-ware. Choose containers with shapes and colors that add a sculptural quality to the garden. The size of the container should be large enough to prevent frequent drying. I recommend pots of eighteen to twenty-four inches, or larger, for small trees and shrubs.

To prevent breakage of stoneware containers it is essential that the pots are filled with potting soil throughout the winter. If empty, they will fill with water and freeze. Freezing and expanding ice will even break granite. Raise the container off the ground by setting it on several bricks to ensure drainage. This will also prevent stress fractures that occur when the bottom of the pot freezes to the ground and the top is warmed by the winter sun.

Drainage is the most important factor in the potting mix. A coarse mixture composed of composted bark, peat-moss, perlite and loam works well. Contrary to the culture given to tender tropicals to promote continuous bloom and new growth, hardy trees and shrubs should not be fertilized frequently. As with any container, watering is essential, especially into the fall. Unlike bonsai, permanently potted trees and shrubs do not need a regime of root pruning and repotting. They will reach and maintain an equilibrium of top growth to roots.

Favorite plants that survive and even thrive in containers year-round include: pine, falsecypress, spruce, elm, arborvitae, birch, ninebark, willow and many more. Explore our display gardens at Tranquil Lake for inspiration for your permanent pots.

Warren Leach

Short in Stature  -Big in Beauty

Diminutive perennials and shrubs, that reach only a mere foot or less in height, have a tremendous value in planting borders and landscapes. Their diversity of use in the garden is certainly disproportionate to their stature. In the foreground of a mixed border they face down taller plants, soften edges, echo colors of other flowers and foliage and cohesively tie together the composition. These tiny gems are delightful in monoculture blankets of groundcovers or sprinkled throughout the border. You can also create wonderfully colorful and textured tapestries within the cracks and crevices of stepping stones paths and terraces.

At Tranquil Lake Nursery, we planted this type of tapestry along one bluestone walkway. Allium senescens ssp. montanum, a dwarf ornamental onion sports six-inch straps of glossy leaves and pink flowering spheres in July. Golden thyme (Thymus vulgaris ‘Aureus’) and Heuchera americana ‘Dale’s Variety’ mingle in front of the miniature red daylily (Hemerocallis ‘Pardon Me’), Hydrangea arborescens ‘Annabelle’ and Phlox paniculata ‘Nora Leigh’. The fine textured foliage of the thyme and allium contrast with the larger scalloped leaves of coral bells (Heuchera). This compositional theme of contrasting scale and color is also carried out in the planting of the daylily, hydrangea and phlox. The short plants in the foreground complete the picture.

I like to use plants that creep and crawl over gravel paths or garden edges made from pieces of stone set in grass. Mediterranean herbs such as thyme and oregano love to bask in hot, dry sunny conditions. Golden marjoram (Origanum vulgare ‘Aureum’) and Origanum laevigatum ‘Herrenhausen’ are two of my favorites. The golden marjoram’s chartreuse foliage is a refreshing color and looks great against the dark maroon of Sedum ‘Bertram Anderson’ or with the felted silver leaves of lamb’s ears (Stachys byzantina ‘Silver Carpet’).

Origanum laevigatum ‘Herrenhausen’ has mats of dark, green-red flushed foliage and blooms in August and September with violet bracts that hold their color into October -- even through frost. Combine with the dwarf form of New England aster (Aster novae-angliae ‘Purple Dome’), the very dwarf Spiraea japonica ‘Golden Elf’ and the starry gold flowers of Coreopsis verticillata ‘Zagreb’ to face down a sunny border of daylilies, Russian sage (Perovskia), catmint (Nepeta x. faassenii), Rudbeckia fulgida ‘Goldstrum’ and the golden leaved ninebark (Physocarpus opulifolius ‘Nugget’). In the front of the border, I like to use dwarf shrubs with foliage color that echoes back, as illustrated here by the Golden Elf spiraea and the Nugget ninebark.

Another favorite and versatile low-growing shrub is Berberis thunbergii ‘Golden Nugget’. A recent field study at Longwood Gardens in Pennsylvania found that this cultivar produces few or no viable seeds. In addition to this redeeming trait Golden Nugget barberry has a cast-iron constitution and will thrive in dry shade as well as dry sun conditions, and even in permanent pots above ground all winter. The fine textured chartreuse leaves make a smashing combination with the round pleated foliage and foamy chartreuse flowers of Lady’s Mantle (Alchemilla mollis).

Add additional creeping yellow- foliaged beauties such as Veronica prostrata ‘Aztec Gold’ and Lysimachia nummularia ‘Aurea.’ Then set ablaze a smoldering simultaneous contrast with the scarlet-red daylily ‘Scarlet Prince’, red beebalm (Monarda ‘Jacob Cline’), Rosa ‘Euopeana’ and the maroon foliaged smokebush (Cotinus coggygria ‘Velvet Cloak’).

The cranesbill geraniums offer a host of hardy varieties to use in the front of the border as well as marry taller perennials and shrubs. A favorite is the indestructible big-root geranium (Geranium macrorrhizum). It will grow in sun or shade, blooms with rose-magenta flowers and has handsome round-lobed leaves that turn red in late fall and remain semi-evergreen all winter.

Combine the round leaves of geranium with the grassy foliage of prairie dropseed (Sporobolus heterolepis) along with Allium senescens ssp. montanum and sedums. This combination adorns the front of one border at the nursery, cascading onto wide granite edging. Behind them are tall sedums, daylilies, thread-leaf coreopsis, bluestar, (Amsonia) and Siberian iris. An adorable, short Siberian iris that is perfect for the front of the border is ‘Precious Doll’. Combine it with the trifoliate leaves of alpine strawberry (Fragaria vesca ‘Alexandria’).

Low growing plants that have flexible stems, such as thyme, are well suited for high traffic areas. The succulent and brittle stems of sedums will withstand footfall if protected within the crevices of stepping stones. One plant that’s under-appreciated although, perhaps overly misused is creeping moss-phlox (Phlox subulata). This phlox grows as a low evergreen mats in sunny locations and can even be mowed. Its cultivars bloom in a myriad of Easter egg colors -- pinks, lavenders and white.

I used Phlox subulata ‘Emerald Cushion Blue’ as the predominate planting in a driveway with pea- stone gravel mulch and infrequent tire traffic. Planted along with the phlox are thymes, golden marjoram, Persicaria affinis, Veronica prostrata, and Potentilla tridentata. Try these low-growing spreading plants in a variety of locations.

Epimedium is certainly one of the stars in the foreground of the shady border. Their diverse, attractive leaves and exotic-shaped flowers, as well as hardy constitution is directly related to their barberry family (Berberidaceae) heritage. Combine epimediums with the narrow leaves of sedges (Carex) and the evergreen glossy foliage of Bergenia as a foil to larger Hosta and Cimicifuga in a shady garden. Combine epimedium with European ginger (Asarum europaeum) and Berberis thunbergii ‘Golden Nugget’ for a stunning combination in front of the blue leafed Hosta ‘Halcyon’ and pendulous yellow bells of Kirengeshoma palmata.

There are a multitude of planting combinations that you can try using these short perennials that mingle, mix and happily marry the border together.

Warren Leach

Recommended Diminutive Plants for the Garden

 Short in the Sun