Hardy conifers that evoke the tropics.

Conifers are iconic trees, though they are not necessarily what comes to mind when you picture an exotic lost world. Of course, if you've seen BBC's Walking With Dinosaurs series, you've seen a tropical conifer island: New Caledonia. Podocarpaceae, Araucariaceae, and Cupressaceae make up a significant part of the flora on this relatively small splinter of ancient Gondwana. According to The Gymnosperm Database, New Caledonia holds 3 endemic conifer genera and 43 endemic conifer species. Actually, New Caledonia has no non-endemic conifers, and its conifer biodiversity is rivaled only by New Zealand (103,738 square miles), Sichuan (187,259 square miles), and California (163,696 square miles)...and, at a mere 7,172 square miles, New Caledonia is much smaller.

Araucaria columnaris on the Isle of Pines, New Caledonia.
Photo by Rene Moutouh.

Araucaria bidwilli. Photo by S. Rae.

So, how does a gardener capture the look of these tropical conifers in a temperate zone? Well, if you live in a more moderate climate (say, USDA zone 7-10 with sufficient rain), then you could always plant the hardier Araucaria araucana, or Monkey Puzzle Tree. They grow well in the boreal rainforest of the Pacific Northwest. However, in Colorado's USDA zone 5 the winters are simply too brutal, in spite of the fact that we seem to be edging toward USDA Zone 6. This is a land of extremes, and though I haven't tried killing any podocarps or araucaria yet, I doubt they would survive the frigid stretches of our coldest potential winter temperatures, not to mention Colorado's tendency to warm up early in the spring only to be followed by a limb-shattering cold snap the following month.

Back to the question. Does this mean there are no tropical-like conifers for Colorado? Well, with the right siting there might be a few...

Cryptomeria japonica 'Araucarioides'
A cultivar of Japanese Cedar, the name says it all. Also known as the Whipcord Japanese Cedar, the needles are held tightly to the branches, giving it a very Araucaria-like look (hence its cultivar name). Hardy to USDA Zones 5/6 through 9, the Whipcord Japanese Cedar is a perfect candidate for a pseudo-tropical garden. It should be situated away from drying winter winds, an important consideration in Colorado. Cryptomeria prefers moist, well-draining soil, and its growth is fastest in humus-rich soils. Not the conifer to plant if drought is an issue, an equally important consideration in Colorado. Still, if these environmental conditions can be met, there is really no reason why Cryptomeria japonica 'Araucarioides' could not be attempted. Purported to remain much smaller than the species, the Whipcord Japanese Cedar should reach a height of 15 feet at maturity, its foliage increasing in fullness as it grows. Again, success with this conifer will undoubtedly be determined by microclimate and siting. Still, some sources do indicate that Cryptomeria can be drought-tolerant once established.

Cryptomeria japonica 'Araucarioides'.

Pinus x schwerinii 'Wiethorst'
A cultivar originating from a witches' broom found on a hybrid between Pinus strobus (Eastern White Pine) and Pinus wallichiana (Bhutan Pine). Pinus strobus contributed an increased hardiness, Pinus wallichiana contributed long needles, and the witches' broom contributed a manageable size for smaller gardens. The longer, graceful needles are reminiscent of the tropical Central American pines and sub-tropical Mexican pines, so Pinus x schwerinni 'Wiethorst' definitely evokes the tropics. With space, the original Pinus x schwerinii could offer, albeit on a grander scale, the same effect as its dwarf clone. Pinus x schwerinii 'Weithorst' was one of two conifers chosen by the American Conifer Society as their 2014 Collectors Conifer of the Year.

Pinus x schwerinii 'Wiethorst'.
Photo by Sean Callahan, American Conifer Society.

Sciadopitys verticillata 'Sternschnuppe'
This is a narrow, upright cultivar of the Japanese Umbrella Pine, a monotypic genus whose fossil record dates back about 230 million years. Any Sciadopitys cultivar would make a stunning specimen conifer in the pseudo-tropical garden. Despite its exotic look, the Japanese Umbrella Pine is definitely not tropical. Hardy to USDA Zones 5 through 8, Sciadopitys verticillata, like Cryptomeria japonica, prefers moist, rich, well-drained soil in full sun, though it does prefer some afternoon shade in hot climates (that'd be you, Colorado). It is a slow grower. The Missouri Botanical Garden cautions that it might "not be reliably winter hardy throughout USDA Zone 5", and suggest that it should be planted in a site protected from winter winds. Sciadopitys verticillata 'Sternschnuppe', commonly known as the Shooting Star Japanese Umbrella Pine, has thicker, broader, and shorter needles than the species, creating "a uniquely appealing texture not found in other conifers", according to Iseli Nursery. On the downside, this species can be subject to snow and ice damage during the winter, so it does require extra attention regarding snow loads. Still, Sciadopitys is an amazing tree that never fails to garner attention in the garden.