Stunning mini-garden that will boost your fall garden. It includes Acorus gramineus ‘Oborozuki’. Bergenia cordifolia, Sedum spurium ‘Voodoo’ and Sedum rupestre ‘Angelina’. Photo: Claude Vallée
September is approaching and that means the end of the gardening season, doesn’t it? After all, frosty days will soon be at hand and most of your garden’s flowers are going rapidly downhill. But an astute professor of horticulture has discovered a way of keeping your landscape full of brilliant color well into December—even right through the winter in milder climates—by planting frost-hardy plants in containers.
Claude Vallée teaches horticulture at the Institit de Technologie Agroalimentaire in Saint-Hyacinthe, Quebec and was looking for a new angle to the strictly spring-and-summer gardening hobby. Specifically, would it be possible to spice up the fall garden with containers of frost-hardy plants? So, he began experimenting and came up with a wide range of plants that would fit the bill … and also some really great designs!
Frost-Hardy to 14?F (-10?C)
Vallée tested over 400 plants for potential use in fall containers. Most flowering plants quickly fell to the wayside: their blooms were damaged by the slightest frost, although there are a few exceptions, like pansies and heathers. On the contrary, many foliage plants come through early frosts or even the first snows in mint condition. This included annuals, perennials, small shrubs and conifers, even some aromatic herbs and vegetables.
Vallée discovered that plants hardy to 14?F (-10?C) were tough enough to sail through September and October, even well into November in most years even in the cold Quebec climate. Some even hardier plants made it to Christmas, putting up with 5?F (-15?C) nights. In zones 5 to 7, both categories would be fine until Christmas. In zones 7b to 9, they’re good for the entire winter!
There were some surprising finds, too. Who, for example, would have thought that the eucalyptus, which we usually think of as a subtropical tree, would hold on right through the fall, even when touched by repeated frosts!
Pot’em Up in Late August
At first Vallée tried to create 3-season container gardens in the spring with the idea they’d last through the fall, but quickly found many plants became overgrown or, if the summer was hot, petered out by September. Instead, the ideal time to prepare the containers was in late August or early September … just when they start to become useful!
The technique is simple enough. All you need is a 2-gallon (7.5 l) container with a drainage hole, lightweight potting mix and assorted plants, most available in any garden center. You may already have many of them growing in your garden, in which case just dig up a few divisions.
Fill the container to within 3 inches (7 cm) of the brim with mix (no need for a “drainage layer”), remove the plants from their pots and dig individual holes so as to set each at their original depth. Fill in around the plants with mix and water thoroughly. Now, water weekly with a dilute solution of a soluble all-purpose fertilizer.
It’s that simple! No pinching, pruning or fussy maintenance is required. And since the plants are barely growing in the fall and therefore need little light, these containers will do equally well in sun or shade. Even watering needs are reduced compared to summer containers: there is simply less evaporation in the fall, so a weekly watering is inevitably sufficient.
Pretty as these plants are in the fall, don’t expect to overwinter there, at least not if you live in zones 7 or colder. Winter will eventually do them in, as even hardy plants freeze more deeply in pots than they do in the ground. And since you’ll be using them to decorate your yard until nearly Christmas, it will likely be too late by then to plant them in the recently frozen ground. So, take this as a life lesson and learn to let go…
Of course, we all know full well that many gardeners are simply incapable of letting a plant die, so there is the one possible way of saving them. Place the container in a protected spot in December, such as a slightly heated garage or up against the house (in the latter case, cover them deeply with fall leaves). The annuals will, of course, die, but maybe—just maybe!—some of the perennials and shrubs may still be alive in the spring.
Plants for Fall Containers
Here are descriptions of some choice plants for all containers, all hardy enough to survive to 14?F (-10?C) at least. Flowers are only mentioned if the plant will be blooming in the fall (most will already have bloomed earlier in the summer).
Angelina Stonecrop (Sedum rupestre ‘Angelina’): A creeping stonecrop with thick, dense “needles” of golden yellow that become orange yellow in fall.
Bergenia (Bergenia crassifolia, formerly B. cordifolia): Thick, rubbery spoon-shaped leaves, dark green at first but becoming purple as the weather cools. The giant leaves of full-grown plants can overwhelm smaller containers: prefer young plants.
Blue Rush (Juncus inflexus ‘Blue Arrow’): Upright, clumping, grasslike plant with blue-green leaves.
Bugleweed (Ajuga reptant cvs): There are dozens of cultivars of this low-growing groundcover with green to purple to variegated leaves. You probably won’t have to buy plants: just dig a clump out of your flower bed!
Conifers (Thuja occidentalis, Chamaecyparis spp., Picea spp., etc.): Look for young plants of these evergreens rather than commercial-size plants: the latter are expensive and too large for most containers. You may be able to find a few self-sown conifers in your yard for free!
Cordyline (Cordyline australis, often sold as C. indivisa): The classic “dracaena spike” used in summer containers, with its narrow, arching green leaves, easily takes -10?C and keeps on looking good. A more colorful version is ‘Red Star’, with deep purple-red foliage, or try any one of the variegated ones, like ‘Torbay Dazzler’ or ‘Cherry Sensation’.
Dusty Miller (Senecio cineraria): Deeply cut ever-so-silver leaves on a compact upright plant. Surprisingly hardy for a plant sold as an annual!
English ivy (Hedera helix cvs): Popular houseplant and container plant with creeping, weeping stems and star-shaped leaves in green, gold or green and white. Root a few cuttings in mid-August and stick them in the container!
Eucalyptus (Eucalyptus gunnii): Rounded silvery-blue leaves on reddish stems. It’s a tree in Australia … but never more than a shrub when grown as an annual.
Flowering Cabbage (Brassica oleracea): The centers of the big rosettes of blue-green to reddish leaves react to cold by turning red, pink or white, looking like a giant rose. Leaves can be entire or fringed. Flowering kale (B. oleracea acephala) produces a stem rather than a rosette, but is otherwise similar. ‘Redbor’ kale, with deeply cut purple leaves, is a popular choice. In December, harvest cabbages and kales and cook them up: ornamental or not, they are still cabbages and will taste especially good after having been frosted (cold brings out their sugars).
Heather (Calluna vulgaris): Small shrub with short, needlelike leaves. Covered all through the fall in tiny bell-shaped blooms in shades of magenta, pink, red or white. If the flowers freeze, not to worry: even when dead, they hold their color!
Heuchera (Heuchera × hybrida): Rosette of colorful maple-shaped leaves in a wide range of colors, from golden to orange to purple to silver, hey, even green! You could do nothing but put heucheras in pots and still have a great fall display!
Lavender (Lavandula angustifolia): Clumping, upright plant with narrow dark green wonderfully aromatic leaves. ‘Silver Edge’ (the name says it all!) is particularly attractive in containers.
Leatherleaf sedge (Carex buchananii): Clumps of narrow reddish-brown leaves make this grasslike plant stand out from the others.
Lemon thyme (Thymus ‘Golden King’ [sold as T. × citriodorus ‘Variegatus’]): Creeping habit. Small leaves edged in gold. The whole plant is delightfully lemon scented.
Pansy and viola (Viola spp.): Among the hardiest flowering plants. The flat-faced blooms can be plain, moustachioed or blotched and come in every shade imaginable. Look for young plants just starting to bloom (mature ones tend to fall to pieces when transplanted).
Periwinkle (Vinca minor and V. major): The first is hardy to zone 4 when grown in the ground, the second not so much so (zone 8), but both produce creeping stems of dark shiny green leaves that drape beautifully over pot edges. Variegated varieties are especially choice!
Purple wood spurge (Euphorbia amygdaloides ‘Purpurea’): Clusters of upright stems with narrow, deep purple leaves. Stunning when touched with frost!
Sage (Salvia officinalis): Beautifully textured and highly aromatic gray-green leaves on short stems. Try ‘Tricolor’ (purplish green with a white and pink margin) or ‘Icterina’ (green and yellow).
Variegated Japanese sedge (Carex morrowii ‘Variegata’): Perfect mound of narrow arching grasslike leaves with creamy centers and green margins. Other cultivars feature inverted variegation or are more intensely yellow and green.
Variegated sweet flag (Acorus gramineus ‘Oborozuki’): Clumps of narrow green leaves striped yellow make this aroid look much like a grass. ‘Ogon’ is similar.
Voodoo stonecrop (Sedum spurium ‘Voodoo’): There are lots of green, reddish and variegated forms of this sedum, but ‘Voodoo’, with its deep mahogany red leaves, is the most colorful. The small leaves are succulent with scalloped edges.
Weeping rosemary (Rosmarinus officinalis ‘Renzels’ Irene™): A creeping to trailing variety of rosemary with pinelike “needles” that are suavely scented. For an aromatic thrill, run your fingers through the leaves each time you pass!
Wintercreeper (Euonymus fortunei cvs): Cultivars with variously variegated leaves of this low-growing shrub or creeper are widely available. Although the mature form is sold as a hardy shrub (well, hardy to zone 5 if grown in the ground, that is!), you may have to look for the young plants you’ll need in the houseplant department!
Fall containers: so simple, so beautiful. Why haven’t you been preparing them your entire gardening life?