Picea

Colorado blue spruce (Picea pungens) is a narrow, stiffly pyramidal conifer from the central and southern Rocky Mountains, and the source of nearly every silver-blue evergreen in cultivation. The colour is real and is the reason it is planted: the needles carry a waxy bloom that reads anywhere from grey-green to an almost metallic pale blue, sharpest on selected cultivars. In its native range, between roughly 6,000 and 11,000 feet from Wyoming and Idaho south to Arizona and New Mexico, it is a cool-climate mountain tree of moist stream sides and canyon bottoms. Planted far outside that range - which is where most people meet it - it is one of the most reliably disappointing conifers in the eastern United States, where humid summers bring on needle cast and cytospora canker and a fifteen-year-old specimen often loses its lower branches and never recovers them. It is also planted far too small: the nursery pyramid becomes a 30-to-60-foot tree. Given cool air, full sun, room, and honest expectations, it is superb and long-lived.

A large, fast-growing European evergreen conifer reaching 40 to 60 feet (sometimes far taller in age) with a broadly pyramidal crown and a distinctive habit: the main branches sweep upward or outward while the slender secondary branchlets hang straight down in graceful, drooping curtains. Stiff, four-sided dark-green needles clothe the twigs, and it bears the longest cones of any spruce - pendulous, cylindrical, 4 to 6 inches long, ripening from reddish to tan-brown. Long planted in North America for windbreaks, tall screens, Christmas trees, and timber, it is cold-hardy and adaptable in cool climates but is NOT heat-, drought-, or humidity-tolerant and falters toward the warm (zone 7) edge of its range.

Oriental spruce (Picea orientalis) is the handsomest spruce in cultivation and the one most often sold on a claim nobody has actually substantiated. Its real distinction is measurable and not in dispute: at 0.2 to 0.3 inches it carries the SHORTEST needles of any spruce, glossy, dark green and four-sided, packed so tightly on the shoot that the foliage reads as a fine dense pelt rather than as separate needles - a texture no other spruce in this catalogue matches. The RHS describes it as a large evergreen conifer of dense conical habit and holds an Award of Garden Merit for the straight species, not merely for a selection. What is NOT established is the line the nursery trade repeats, that it shrugs off heat and humidity where Norway spruce fails. Popular horticultural writing says both things about this tree, sometimes in the same paragraph, and no careful source consulted for this record - the RHS species page, Wikipedia, and the Kew distribution rows - carries a summer-heat or humidity statement at all, so this record assigns no heat range rather than pick a side. Missouri Botanical Garden has NO species page for it, only cultivars, so no MBG text is cited here either. Three further honest caveats. It is SLOW - Wikipedia notes it is grown for timber and Christmas trees less than Norway spruce precisely because of that - and slow on a tree that wants 50 to 70 feet in cultivation is a decades-long commitment, not a garden project. Almost everything on a garden-centre bench is a named cultivar, from the gold-shot forms to the compact and weeping ones, and those are different plants at different sizes from the forest tree described here. And the RHS pest list for the species is the ordinary spruce list - adelgids, red spider mite, conifer aphid, with honey fungus on the disease side - so it is not exempt from what makes spruce difficult in a warm garden.

Red spruce (Picea rubens) is the best-documented case of a tree damaged by air pollution anywhere in the world, and that is the honest headline rather than anything horticultural. Through the 1970s and 1980s, high-elevation stands across the Adirondacks, the Green Mountains and the central and southern Appalachians lost roughly a quarter to a half of their canopy trees. The mechanism took twenty years to pin down and turned out to be indirect: acid fog and mist leach calcium out of the needle cell membranes, and decades of acid deposition strip exchangeable calcium out of already-poor soils while mobilising aluminium that is toxic to fine roots. A calcium-starved needle loses cold tolerance, so the tree is killed not by the acid but by an ordinary winter it should have survived. The controlled proof came from Hubbard Brook in New Hampshire, where a watershed refertilised with calcium silicate in 1999 lost roughly a third as much current-year foliage as the untreated reference watershed in the severe winter-injury year of 2003, the reference losing about 75 per cent of it. The ending is genuinely good news, which is rare in this catalog: after the 1990 Clean Air Act Amendments cut utility sulphur dioxide by around forty per cent, more than three-quarters of monitored red spruce have been growing faster since about 2001. The second thing to know is that this is the tonewood - the Adirondack spruce of pre-war Martin guitars, still the premium soundboard for steel-string guitars, violin bellies and piano boards, and priced accordingly after mid-century overcutting. The third thing is the caveat the Lady Bird Johnson Wildflower Center states flatly: this species is not well suited to cultivation. It wants cool foggy montane summers, permanently moist acid ground and no lime, its roots sit in the top foot of soil so it blows over, and it is often defoliated by spruce budworm. Plant it because you are restoring an Appalachian or northeastern spruce forest, not because you want a garden conifer.