Intermediate Conifers: Creating Variety in your Garden
Looking to spice up your landscape? Find out more about “the forgotten conifers.”
In the two most recent installments of Conifer Corner, I’ve been discussing outstanding conifers in each of the four size categories recognized by the American Conifer Society (ACS), beginning with the smallest size category (Miniature conifers) and working up to larger conifers. In this edition of Conifer Corner, I continue this discussion by considering Intermediate conifers.
The ACS defines intermediate conifers as those that grow 6-12” per year and reach a height of 6’ to 15’ at age 10. They are not adorable little miniatures or dwarfs that can fit into a container or rock garden. Conversely, intermediates won’t dominate a landscapeas a specimen, like a large conifer. Nevertheless, intermediate conifers are an important group of trees because they fulfill an important function in landscape design and development.
Unlike their smaller cousins, miniature and dwarf conifers, intermediate conifers are less likely to get “lost in the shuffle” in a busy landscape design. Unlike large conifers, intermediates are less likely to interfere with power lines or other overhead obstruction and are better suited to planting closer to houses and allow greater flexibility in site selection.
As with all of the trees that I’ve discussed in this series on conifers in the ACS size classes, there is considerable variation in growth depending on site and cultural practices. This is especially true with intermediates. Some intermediate conifers growing on a good site could reach a size comparable to large conifers.
There is no single “official” trial garden where conifer sizes are determined. Size classes are based on observations by growers and conifer enthusiasts and a given cultivar may be listed as an intermediate in one reference and as a large in another. In general, size classes referred to in Conifer Corner articles are based on the ACS Conifer Database.
Intermediate Conifers for the Central Region
Pinus cembra (Swiss stone pine)
Conifer expert Chub Harper has a passion for plants that is matched by few and few plants get him as excited as Pinus cembra. Just mention Pinus cembra and Chub goes all Will Rogers. “I’ve never met a cembra I didn’t like," Chub enthuses. “This is one of those plants I just don’t understand why we don’t use more.” Indeed, it’s easy to understand Chub’s swooning for Swiss stone pine. This species maintains a tight compact form with a straight single leader, giving it a stately elegance without pruning.
Moreover, Pinus cembra has beautiful blue green needles that often take a silvery sheen. Cembra is fairly tolerant of a range of sites and is variously listed as zone 3 or 4, so it is hardy in most of the Lower Peninsula. Pinus cembra is one of those plants that even the straight species is distinctive enough tomake an impression. In addition, there are a number of cultivars on the market. Note that some of the cultivars included here fit into the Dwarf size class.
- Pinus cembra ‘SilverSheen’
A striking cultivar of P. cembra with silvery blue needles. Zone 5.
- Pinus cembra ‘Chalet’
A pyramidal to upright form of Pinus cembra. There is a terrific specimen in the Harper Collection. Zone 4, though also reported to Zone 3.
- Pinus parviflora (Japanese white pine)
A solid performer in Michigan. There are a variety of cultivars of Japanese white pine, some of which I’ve mentioned in earlier Conifer Corners.
- Pinus parviflora ‘Bergman’
This is one of the more striking forms of Japanese white pine, with twisting bluegreen needles. Variously listed as a dwarf or an intermediate.
- Pinus parviflora ‘Fukuzumi’
The formon this plant can be variable, but its recurved blue-green twisted needles give it consistent appeal.
Chamaecyparis pisifera ‘Filifera Aurea’ (Golden thread false cypress)
Yes, the Latin name is amouthful, but this plant is a show-stopper like few others. ‘Filifera Aurea’ generate interest from a distance due to their bright yellow color and upright weeping form, as well as up close due to their impossibly long threadlike foliage.
Abies concolor ‘Conica’
Continues the theme of color – this time striking blue. Abies concolor ‘Conica’ also continues the theme of underused conifers. This tree’s stately upright form makes it a prime choice as a specimen plant. Put one of these in your yard and you’re guaranteed to have all of the neighbors asking “Whatzzat?”
Picea glauca ‘Pendula’
Technically this is listed as an intermediate, but on better sites it may push toward the large category. Also, this cultivar has been around long enough that it’s possible to find some decades-old larger specimens. The tight form and drooping branches make it easy to envision this plant in a snow-blanketed mountainside.
Abies koreana ‘Silberlocke’
Gets double marks for showmanship. The needles on this cultivar of Abies koreana are highly recurved, that is, they are turned upward to reveal their silvery underside. While that alone is enough to give the tree tremendous ornamental appeal, ‘Silberlocke’, like most Korean firs, also produces prodigious amounts of colorful cones. Although cones on firs make Christmas tree growers cringe, in this case it adds to the plant’s landscape appeal.
Abies lasiocarpa var. arizonica (Corkbark fir)
An argument for the lumpers and splitters. Some references list this as a variety or even sub species of Subalpine fir (A. lasiocarpa) while others (for example, the Gymnosperm database) list corkbark fir as its own species (A. bifolia). In the nursery trade, var. arizonica holds sway. Another high elevation conifer from the mountain southwest, corkbark fir is a striking tree that can often match Picea pungens for blue color.
Larix kaempferi ‘Pendula’
Deciduous conifers always make a unique contribution to the landscape and this weeping larch is no exception. This plant commands interest anytime during the growing season, but especially in the early spring when the new bright green needles are just begining to flush. According to the ACS, this tree is widely mislabeled as Larix decidua ‘Pendula’.
Picea pungens ‘Walnut Glen’ (Walnut Glen Colorado blue spruce)
Is an interesting twist on the old standby, Colorado blue spruce. This P. pungens cultivar has a golden cast to its needles, which often make it look like the sun is shining on it even when it’s in the shade. Reportedly adapted to a fairly wide range of site conditions though the variegated yellow needles may suffer scorch under stress.
Pinus aristata (Bristlecone pine)
We can’t really recommend bristlecone pine as an outstanding grower in Michigan, but it’s a fascinating tree and it will grow on suitable sites here in Michigan. In their native habitat, bristlecone pines are among the oldest living things on earth. The Rocky mountain form (P. aristata) can live to nearly 3,000 years old and specimens of the Great Basin form (P. longaeva) have been found that are over 4,800 years old. Although we don’t expect a Bristlecone pine to live thousands of years in Michigan (and, in any case, we won’t be around to see it), this makes an interesting specimen in the right spot. Look for a site with good drainage and relatively good air flow. Like many trees adapted to the arid west, these pines don’t like wet feet or high humidity.
Thuja occidentalis ‘Degroot’s Spire’
In general, arborvitae are the kinds of plants that don’t usually get people too excited. However, this upright columnar form makes a great accent and can add a formal appearance as a border or can be grouped for effect.
Thuja occidentalis ‘Hetz Wintergreen’
Another upright form of arborvitae. ‘Hetz Wintergreen’ is noteworthy for a couple of reasons. It tends to maintain its green color throughout the winter when many other conifers turn off-color and it tends to maintain a strong central leader, whereas many columnar arbs can develop multiple leaders or bend over under snow loads. Excellent for a year-round screening hedge and windbreak.
Picea omorika ‘Pendula Bruns’ (Weeping Serbian spruce)
It’s always hard to go wrong with a Serbian spruce. ‘Pendula Bruns’ is a little slower growing and has a little tighter form than ‘Pendula’and ‘Berliners Weeper’ – more on those two in the next Conifer Corner.
Picea glauca 'Densata’ (Blackhills spruce)
Depending on the reference, Black hills spruce is listed as either a true botanical variety (var. densata) or simply as a cultivar. Regardless of the taxonomy, this is a versatile tree that we’ll likely see more of in the future. As the Latin name ‘Densata’ implies, Black hills spruce has a tight, dense growth habit and maintains a nice pyramidal form. Its growth rate is slower than the straight species or blue spruce so it’s less likely to get out of hand and provides more flexibility in site selection. With its uniform compact growth, Black hills spruce also shows promise as a table top Christmas tree.
Text and photographs by Dr. Bert Cregg. Additional photograph by Jack Wikle.
Dr. Bert Cregg is an Associate Professor in the Departments of Horticulture and Forestry at MSU.
This article was originally published in the Winter 2010 issue of Conifer Quarterly and the October 2007 issue of The Michigan Landscape magazine, a monthly publication of the Michigan Nursery and Landscape Association. It was the third of a four-part series in the Conifer Corner section of the magazine. We had arranged to reprint this series prior to the passing of our friend Chub Harper. The references to Chub point to his significance in the world of conifers.
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