Abies

Balsam fir (Abies balsamea) is THE Christmas tree of the northeast and, for most gardens, a tree to admire rather than plant. Missouri Botanical Garden is unambiguous about why: the species is native to cool climates and is not recommended for planting in the hot and humid summer conditions south of USDA Zone 5, it is generally intolerant of urban pollution, and MBG explicitly does not recommend it for its own St. Louis climate. Wikipedia puts the same limit the other way round - it wants a mean annual temperature near 40°F with consistent moisture, and low moisture combined with high temperature is what stops the range. This is a boreal tree. It runs from Labrador and Newfoundland west to Alberta and south to Minnesota, Wisconsin, New England and New York, then survives in the Appalachians only by climbing, hanging on at 2,500 to 5,000 feet as far south as Virginia and West Virginia. Where it does suit the climate it is superb: a narrow aromatic spire of 50 to 70 feet and only 15 to 25 feet wide, clothed in flat blunt needles 0.6 to 1.2 inches long, dark green above with two chalk-white stomatal bands beneath and twisted at the base so they lie in two horizontal ranks either side of the shoot. Two features are worth learning by hand. The young bark is smooth and grey and studded with RESIN BLISTERS that spray when punctured - no spruce or pine does that - and the erect cones, 2 to 3 inches and dark purple, ripen brown and DISINTEGRATE on the branch in September, dropping their scales and leaving a bare central spike standing on the twig. A fir cone is therefore something you almost never find whole on the ground, which is the single fastest way to tell Abies from Picea. That resin is also the reason this tree has a place in the history of optics: Canada balsam, the oleoresin tapped from those bark blisters, dries to a transparent mass with a refractive index near 1.52, effectively the same as crown glass, so it worked as an invisible glue for cementing lens elements and became the standard mounting medium for microscope slides from about 1830. It was phased out during the Second World War for polyester, epoxy and urethane adhesives, which do not yellow and have far better thermal and solvent resistance. The honest catch list is long: balsam woolly adelgid, spruce budworm (this is the budworm's preferred main host), bark beetles, spider mites in hot spells, cankers, heart rot, root rot, needle rust and twig blight, plus heavy deer browsing, shallow roots that make it wind-firm only in a stand, and a working life measured in decades rather than centuries.

A very large montane evergreen conifer of cool, moist European mountain forests, narrowly conical when young and reaching well over 100 feet (often 98 feet and more) at maturity. Its signature is the foliage: flat, blunt, comb-arranged needles that are dark glossy green above and marked beneath with two chalky silvery-white bands, giving the 'silver' fir its name. Mature trees carry upright, barrel-shaped cones high in the crown that ripen and shatter on the tree rather than falling whole. Abies alba is native to the mountains of central and southern Europe - the Pyrenees, Alps, Apennines, Carpathians and Balkans (POWO, Kew) - and it carries that origin into the garden: it wants a cool, moist, sheltered climate and deep, well-drained soil, and it struggles with summer heat, drought, atmospheric pollution and late spring frosts. It is slow to establish and then long-lived, a forest-scale specimen for large, cool gardens and uplands rather than hot or urban sites.

Fraser fir (Abies fraseri) is an evergreen fir endemic to the high-elevation southern Appalachian Mountains of southwestern Virginia, western North Carolina, and eastern Tennessee, where it grows only on cool, moist, fog-drenched summits above roughly 4,000 feet. It is a modest-sized conifer, usually 30 to 50 feet tall with a narrow, spire-like crown, soft flattened dark-green needles with silvery-white undersides, and erect purple cones whose papery bracts curl back over the scales. It is best known as one of the most popular Christmas trees in North America, prized for its balsam fragrance, soft non-prickly needles, and excellent needle retention. The honest catch is that it is a true mountain plant: it needs cool summers, high humidity, and acidic, evenly moist but well-drained soil, and it does poorly in the heat and humidity of the lowland South, roughly anywhere below or south of USDA zone 7. Its wild stands are also in serious trouble - the introduced balsam woolly adelgid has killed the great majority of mature wild trees since the mid-20th century, and the species is assessed as Endangered.

Grand fir (Abies grandis) is one of the great trees of the Pacific Northwest and a poor choice for most gardens, and those are the same fact rather than two: it is built for cool, wet, deep-soiled maritime ground and it is built enormous. Missouri Botanical Garden gives it 100 to 250 feet with a 4 to 6 foot trunk, says it performs poorly in most areas of the eastern United States, and states flatly that it is not recommended for planting south of USDA Zone 6. It is also fast - the coastal form can put on more than 5 feet a year while young - so the mistake compounds quickly, and it is not a durable tree in return: historically it reached nearly 300 years, but 100 is more typical under modern stress. Its bark is thin and it cannot seal a wound with pitch, so fire scars, pruning cuts and logging damage open the trunk to heart rot, and east of the Cascades a trunk carrying Indian paint fungus is rotten inside whether or not the crown looks it. Balsam woolly adelgid, bark beetles, root rot and needle rust are all on Missouri Botanical Garden's problem list, and western spruce budworm epidemics killed grand fir at scale in the eastern Cascades and the Blue Mountains in the late twentieth century. What is genuinely wonderful about it belongs on the label too. The needles are flat, blunt and laid in two neat horizontal ranks like the teeth of a comb, and along one side of a twig they alternate short, long, short - a sawtooth that white fir rarely shows and the quickest way to name the tree. Crushed, they smell strongly of tangerine, which is why it is also called stinking fir, and no other fir in this group smells like it. The cones stand UPRIGHT on the upper branches and never fall whole; they break apart on the tree in autumn and leave a bare spike standing on the branch, which is the single cleanest way to separate any Abies from a spruce or a pine.

Korean fir (Abies koreana) is a compact, slow-growing evergreen fir from the high mountains of southern South Korea, where it is confined to cool, misty summits, most famously Hallasan on Jeju Island. In gardens it makes a dense, neat, conical small tree, usually 15 to 30 feet over many years, with short broad needles that are dark green above and marked beneath with two vivid white bands, so the whole tree flashes silver when the wind turns the foliage. Its signature is the cones: erect, cylindrical, and an intense violet-blue when young, and unusually it bears them freely even on young plants only a few feet tall, which is why it is one of the most collected ornamental firs and holds the RHS Award of Garden Merit. The honest catch is that it is a true mountain conifer: it wants cool summers, steady moisture, and acidic, well-drained soil, and it resents heat, drought, and urban pollution, so it disappoints in hot lowland gardens south of about USDA zone 7. It is also Endangered in the wild, where warming is widely blamed for pushing its shrinking high-altitude stands, most visibly on Jeju, further up the mountains.

Subalpine fir (Abies lasiocarpa) is the narrowest conifer in western North America and, for most gardens, the wrong tree. It is a timberline species: the US Forest Service silvical account puts its climate at a mean July temperature of 45 to 60°F, with more than 24 inches of precipitation of which much falls as snow, on ground that is frozen or under snow for a large part of the year. Bring it down the mountain into a hot summer, a humid one, or a polluted one and it sulks, thins and dies, and it does so slowly enough that people keep watering it. The Lady Bird Johnson Wildflower Center calls it a spire-like evergreen of 30 to 50 feet with stiff horizontal limbs branched to the ground, and that spire is the whole ornamental argument - a crown so narrow it can be a fifth as wide as it is tall, which is a snow-shedding adaptation rather than a nursery selection. At and above treeline it stops being a tree at all and grows as krummholz, low sprawling mats scoured by wind, and reproduces by LAYERING: a branch pressed into the ground roots and becomes a new stem, so a single tree can leave behind a ring of clones that mountaineers call an atoll. Two honest problems follow it down into cultivation. It is slow and, for a conifer, short-lived and structurally weak - thin bark, persistent dead branches, easily windthrown - and its pest list is serious: balsam woolly adelgid (Adelges piceae), introduced from Europe and the most destructive insect on this species in the Cascades, and the western balsam bark beetle (Dryocoetes confusus), which together with Armillaria root rot drives the mortality complex that has killed subalpine fir across large areas of the Rockies. Like every true fir it carries its cones UPRIGHT on the upper branches, dark purple ripening brown, and those cones never fall whole - they shatter on the tree and leave a bare central spike standing on the branch, which is the single quickest way to tell an Abies from a Picea at a glance.

White fir (Abies concolor) is a large evergreen conifer of the mountains of the western United States and into northern Mexico, grown in gardens for its soft, blue-green needles and neat, narrowly pyramidal form. The needles are long for a fir - roughly 1 to 3 inches - flattened, blunt or slightly notched, and nearly the same pale blue-green on both surfaces, which is the meaning of the name concolor. Its real selling point is adaptability: it stands up to heat, drought, and urban conditions far better than most firs, which makes it one of the few worth trying in the Midwest and the drier interior West where other firs sulk. That tolerance has honest limits - it still does poorly in the heat and humidity south of USDA zone 7, it is slow-growing, and it breaks bud early enough that a late spring frost can scorch the soft new shoots. Grown as a specimen, a screen, and a long-needled Christmas tree, it is long-lived, reaching about 40 to 70 feet in cultivation and well over 100 feet in the wild.