Designing with dwarf conifers

When it comes to conifers, bigger isn’t always better. We may pine for mature Douglas firs and Norway spruces, but those goliaths will swallow up most urban gardens. Thankfully, there are dwarf forms of many conifers, suitable for gardens of all sizes, right down to pots and troughs. Of course, “dwarf” is a relative term. The ‘Fat Albert’ cultivar of blue spruce is often called a dwarf form of Colorado blue spruce, and yes, it is smaller than the 75-foot (22.5-m) species, but it can still reach a pretty hefty 25 feet (7.5 m) or more in time.

The American Conifer Society classifies dwarf conifers as those growing one to six inches (2.5 to 15 cm) a year with a size at 10 years of one to six feet (30 to 180 cm), vertically or horizontally, depending on habit. The key phrase there is “size at 10 years,” which is what most labels and catalogues give, too, when describing a plant’s height and width. But beware, the ultimate height can be considerably more. The lovely dwarf  ‘Nana Gracilis’ Hinoki cypress (Chamaecyparis obtusa ‘Nana Gracilis’), for example, is listed at three feet (90 cm) at 10 years, but can ultimately grow to triple that.

A few dwarf conifers come by their smaller size naturally, but most owe their beginnings to quirks of nature. Some are chance seedlings, such as the dwarf Alberta spruce (Picea glauca var. albertiana) discovered by a railway track in that province in 1904, which are then trialled for garden worthiness. Others start as mutations: when a tree suddenly produces a branch with different growth or colour, which is then snipped off and propagated. Still others spring from “witches’-brooms,” the name for congested twiggy eruptions on the branches of normal trees. Why these Mini-Me growths arise isn’t clear — it could be insects, a fungus or just a genetic anomaly interrupting the growing tips. The story goes that keen plant hunters seeking witches’-brooms, which often occur high up in the trees, would shoot them down rather than risk life and limb climbing up to cut them off.

Many dwarfs in turn produce mutations and witches’-brooms, resulting in ever more tempting additions to plant collectors’ lust lists. As avid “conehead” Robert Obrizok writes of his collecting passion in A Garden of Conifers, “Proceed with caution!”

Whatever their origins, dwarf conifers come in a dizzying array of shapes, textures and colours to play with. While many are conical (although that’s not why they’re called conifers: “conifer” actually means cone-bearing), there are also columnar, oval, spreading, prostrate, mounding, rounded and weeping forms, offering a gamut of creative combinations. Cultivar names such as ‘Pixie’, ‘Teeny’ and ‘Tom Thumb’ are pretty obvious, but the words nana, compacta, minima, pumilus and pygmaeus are indicators of smaller-than-usual size.

The young foliage of many conifers differs from adult foliage, often being finer in texture and different in hue. Some dwarfs exhibit both simultaneously — C. o. ‘Split Rock’, for example, has blue-toned juvenile growth along with green adult foliage. Some such as ‘Rheingold’ white cedar (Thuja occidentalis) have ferny, golden-bronze juvenile foliage only acquiring scaly adult growth with age, while others, such as the little globe cedar T. o. ‘Teddy,’ retain their young foliage even as mature plants, a trait called juvenile fixation.

With textures ranging from soft and feathery to prickly and stiff, dwarf conifers add a distinctive touch to the garden tapestry. And not only with texture, but also with colour. We tend to think of them as just green, but there are also blue, gold, grey-green, chartreuse and multi-hued conifers splashed or banded in yellow, ivory or white.

Many conifers, in fact, change colours over the course of the year: green ‘Rainbow’s End’ dwarf Alberta spruce, for example, is covered in bright yellow new growth tips — like so many little lights — in midsummer; some, such as the ‘Vilmoriniana’ Japanese cedar (Cryptomeria japonica ‘Vilmoriniana’), turn from deep green to russet bronze or burgundy in winter. On top of that are some equally vivid cones, from rich blue-purple on Korean fir (Abies koreana cvs.) to startling raspberry red on dwarf Norway spruce (Picea abies ‘Pusch’), for instance.

A common guideline says one-third of your garden should be composed of evergreens. Given the incredible range of dwarf conifers and the fact that, like potato chips, it’s nigh impossible to have just one, I’m thinking that ratio is sure to go out the window.

Choosing dwarf conifers

Because they’re evergreen (or “everblue,” “evergold,” etc.), conifers add structure, permanence and year-round interest to any garden. One exception is the larch (Larix spp.), which is deciduous and drops all its needles in fall, though it does turn a striking golden tan before doing so. The key is to choose different forms, colours and textures from the extensive conifer palette and combine them for optimal effect.

Darren Heimbecker has been doing just that at Whistling Gardens, his botanical garden and nursery on 20 acres near Brantford, Ont. His collection now features more than 2,500 conifers, including many dwarfs, in a variety of settings. Pressed to name his favourite genera, he says, “The firs, especially the Korean firs, for their colours, soft needles and hardiness; and the Hinoki cypresses, for their beauty and variety, from baseball-sized to really tall trees.”

Across the pond, British plantsman Adrian Bloom integrates more than 500 different conifers, large and small, with trees, shrubs, perennials and bulbs in lush, many-layered plantings in his Norfolk garden. The mix is dynamic, with every plant having its time in the spotlight, yet always contributing harmoniously to the whole.

Bloom counts heathers, small barberries, Japanese maples, little spring bulbs, rock and alpine plants, and low-growing perennials, particularly ornamental grasses, among the best companions for dwarf conifers. Most strikingly, a wide band of Japanese blood grass (Imperata cylindrica ‘Red Baron’) winds through the plantings, intensifying a blue spruce here, a golden juniper there. What Bloom calls his “river of blood” cleverly acts as a unifying link and also draws the eye through the space.

On the other hand, New Englander Robert Obrizok, who was instantly hooked by a trio of diminutive conifers, devotes his garden exclusively to them. Groupings are set like jewels in expanses of neutral mulch or gravel, and a wooden boardwalk offers an ideal vantage point from which to admire them.

Stone and evergreens have a natural affinity, from gravel or pebble mulch to carefully placed rocks in deceptively simple arrangements. Sometimes a well-chosen boulder is the best finishing touch. And of course, full-fledged rock gardens are ideal for displaying conifers, which appreciate the good drainage.

Even a dwarf conifer can be showy enough in its own right to be a focal point — the silvery blue dwarf Rocky Mountain fir (Abies lasiocarpa ‘Glauca Compacta’), for example, which could be set off by spreading or mounding green conifers or a royal mix of purple barberries and dusky coral bells.

But be aware, even disciplined gardeners can put plants too close together — it’s hard to allow sufficient space for ultimate sizes, especially with very slow-growing plants. One solution is to fill gaps with perennials that can be removed as necessary, though it’s important to keep such companion plants in scale. “A medium-sized hosta, for example, would eat a little evergreen for lunch!” says Heimbecker. Further reason to avoid overcrowding is that shaded areas on conifers can result in bald spots, potentially disfiguring the plant. “On most conifers, once it’s gone, it’s gone,” he says.

Upright forms make strong vertical accents, punctuating a border, accenting a path or framing an entryway. Symmetrical, rigid shapes lend themselves to more formal settings, while the spreading, irregular, windswept forms better suit rockeries and informal spaces. Prostrate and spreading conifers can intermingle to drape over walls, create a ground-covering quilt, or clothe a slope for easy maintenance and effective erosion control.

While conifer combinations can be dazzling, multiples of one variety can be used as a mini-hedge, defining or dividing the space and creating continuity. A row of even small conifers can act as a windbreak, producing a microclimate for more diminutive treasures.

Conifers in containers

The petite charms of dwarf conifers can be more closely appreciated in containers and troughs. Young specimens can happily coexist in a container for several years before they outgrow it and need to be transplanted into the garden. Even more ideal candidates are the miniature conifers, classified by the American Conifer Society as those growing less than one inch (2.5 cm) a year and attaining a 10-year size of less than one foot (30 cm). These mini-marvels can work on their own or be combined with small perennials and alpine plants. Indeed, the tradition of creating miniature alpine landscapes in troughs is a long and honourable one, and just as popular today.

Dwarf conifer care

Most conifers like sun, however hemlocks and yews will tolerate some shade. Those with yellow or variegated foliage may need protection from the hottest sun, though conifer maven Jim Lounsbery of Vineland Nurseries, in Beamsville, Ont., cautions that, given too much shade, they may lose their variegation. Dwarf conifers will adapt to most soils and moisture levels, except very sandy and dry. Compost added to the planting area (not just the hole), regular watering and a layer of mulch is appreciated. Lounsbery recommends a fine bark mulch (“cedar is nice as it adds some acid to the soil as it breaks down”) about two inches (5 cm) deep. Fertilizing isn’t necessary, but little conifers in containers, ideally grown in a combination of soil-based mix and sharp sand, should be fed with an all-purpose, slow-release fertilizer at the start of summer.

Harsh winter winds can inflict a lot of damage, so find a sheltered spot for susceptible specimens. Heimbecker also recommends protecting gold and variegated dwarf conifers, if planted in fall, by wrapping them with burlap for the first winter. After that, they should be fine.

Watch for accumulations of dead needles, especially in very compact pines and spruces. Such accumulations can reduce vital air circulation, so should be cleaned out every year or two. And if a large reverting shoot erupts — as may happen from a grafted plant or a witches’-broom — prune it out immediately at the base. Otherwise, the reversion could take over completely and the plant will grow to full, non-dwarf size.

Pruning: Most dwarf conifers require little pruning, but some do benefit from a snip or shear. For instance, Adrian Bloom recommends pruning Tsuga canadensis ‘Gentsch White’ regularly to maintain its variegation and Chamaecyparis pisifera ‘Squarrosa Intermedia’ to keep its pincushion shape. Lounsbery says winter burn on plants can be trimmed back, and some conifers such as the ‘Rheingold’ cedar can be lightly sheared to retain the juvenile foliage. Also, scale is crucial so some might need pruning to maintain the balance in a particular arrangement.

Transplanting: As dwarf conifers grow, albeit slowly, transplanting may be necessary. Early spring is the best time to do this and for all but the smallest ones, root pruning the previous autumn is recommended, especially for pines. This simply means plunging down a sharp spade around the plant’s drip line. This encourages root growth and a tighter root ball, subsequently lessening transplant shock. Heimbecker notes that root pruning is also an effective way to restrict growth and keep plants in bound.

Pests and disease: Dwarf conifers are more prone to pests and disease if stressed — i.e., suffering from drought or waterlogging — so healthy cultivation practices and good air circulation are in order. Keep an eye out for mites and aphids on spruces and firs; bagworms on false cypresses; twig blight on junipers; and fungal diseases and bark beetles on pines.

Thankfully, deer find many conifers distasteful, except for yews and arborvitae and a few firs. (I once complimented a gardener on his shapely, well-trimmed cedar hedge and he laughed, saying, “The deer did it.”) Rabbits nibble indiscriminately, so a low protective fence or individual wire cages may be warranted. I’ve found meat meal sprinkled on and around small plants to be an effective deterrent, though it must be reapplied regularly. On the plus side, birds adore conifers of all sizes for food and shelter.

 Dwarf conifers to consider

Grouped according to form, here is a list of dwarf conifers that offer a wide range of textures, shapes and colours to enhance your garden year-round. Measurements given are approximate 10-year heights or widths, depending on plant form.

Upright

Dwarf blue Rocky Mountain fir (Abies lasiocarpa ‘Glauca Compacta’): Pyramidal form with silver-blue needles; five feet (1.5 m); Zone 5

‘Confucious’ Hinoki cypress (Chamaecyparis obtusa ‘Confucious’): Compact gold cultivar from New Zealand; four feet (1.2 m); Zone 5

‘Nana Lutea’ Hinoki cypress (C. o.  ‘Nana Lutea’): Twisted, golden, fan-like foliage; three feet (90 cm); Zone 5

‘Jean’s Dilly’ dwarf Alberta spruce (Picea glauca ‘Jean’s Dilly’): Green needles and a tidy conical shape; three feet (90 cm); Zone 4

Irregular

‘Bandai-sugi’ Japanese cedar (Cryptomeria japonica ‘Bandai-sugi’): Deep green needles in congested clusters; five feet (1.5 m); Zone 6

‘Porcupine’ blue spruce (Picea pungens ‘Porcupine’): Bright blue foliage; three feet (90 cm); Zone 3

‘Ara-kawa’ Japanese white pine (Pinus parviflora ‘Ara-kawa’): Bluish needles and dark, warty bark; three to six feet (90 cm to 1.8 m); Zone 4

‘Frosty’ Canadian hemlock (Tsuga canadensis ‘Frosty’): Green needles frosted with white; prefers shade; three feet (90 cm); Zone 4

Round

‘Snow’ Sawara false cypress (Chamaecyparis pisifera ‘Snow’): Feathery, white-tipped foliage in spring; three feet (90 cm); Zone 5

Vilmorin’s Japanese cedar (Cryptomeria japonica ‘Vilmoriniana’): Fine-textured green needles turn bronze purple in winter; three feet (90 cm); Zone 6

‘Little Gem’ Norway spruce (Picea abies ‘Little Gem’): A ball of soft green needles on crowded branchlets;  two feet (60 cm); Zone 3

‘Pusch’ Norway spruce (*P. a.* ‘Pusch’): Named Collector’s Conifer of the Year in 2008; covered in bright red cones in spring; three feet (90 cm); Zone 3

‘Smidtii’ Bosnian pine (Pinus heldreichii ‘Smidtii’, syn. P. leucodermis ‘Smidtii’): Mounding pine perfect for rock gardens; 18 inches (45 cm); Zone 4

Spreading/prostrate

‘Silver Mist’ shore juniper (Juniperus conferta ‘Silver Mist’): Silvery blue-green needles; salt-spray tolerant; three feet (90 cm); Zone 6

‘Mother Lode’ creeping juniper (J. horizontalis ‘Mother Lode’): Bright golden sport of ‘Blue Rug’; six feet (1.8 m); Zone 3

‘Gold Spot’ Siberian cypress (Microbiota decussata ‘Gold Spot’): Green foliage flecked with gold; three feet (90 cm); Zone 3

‘Prostrata’ blue spruce (Picea pungens ‘Prostrata’): A true blue creeping form; four feet (1.2 m); Zone 3

Weeping

‘Farnsburg’ Norway spruce (Picea abies ‘Farnsburg’): Can be staked or left to ramble over the ground; four feet (1.2 m); Zone 3

‘Thorsen’s Weeping’ Western hemlock (Tsuga heterophylla ‘Thorsen’s Weeping’): A spreader that’s staked to form a weeping tree; four feet (1.2 m); Zone 5

Miniatures

‘Silberperle’ Korean fir (Abies koreana ‘Silberperle’): Dense upturned needles with silvery undersides; 10 inches (25 cm); Zone 4

‘Golden Sprite’ chamaecyparis (Chamaecyparis obtusa ‘Golden Sprite’): Congested irregular form; holds colour all year; 12 inches (30 cm); Zone 5

‘Tom Thumb Gold’ Oriental spruce (Picea orientalis ‘Tom Thumb Gold’): Gold-brushed needles, nest-like shape; six inches (15 cm) tall and 12 inches (30 cm) wide; Zone 4

‘Dave’s Choice’ mugo pine (Pinus mugo ‘Dave’s Choice’): Little globe-shaped witches’-broom from ‘Mops’ mugo pine; 12 inches (30 cm); Zone 4

‘Hagoromo’ Japanese white pine (P. parviflora ‘Hagoromo’): A sweet Japanese white pine; miniature in all respects; 12 inches (30 cm); Zone 5

‘Sea Urchin’ white pine (Pinus strobus ‘Sea Urchin’): Feathery blue-green foliage on a compact globe; 12 inches (30 cm); Zone 4.