Emerald Knoll Korean BoxwoodBuxus sinica var. insularis 'RLH-BI' (PP# 24,443)
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Buxus sinica var. insularis 'RLH-BI' (PP# 24,443)
Outdoor Growing zone
Full Sun, Partial Sun
The Emerald Knoll Korean Boxwood is a broad, spreading variety that is also dense and billowing, looking great even without trimming. The rich green of the leaves is reliable and constant, without winter bronzing. The small leaves are in perfect proportion to the size of the plant – no more than 2 feet wide and 3 to 4 feet across. Use it for informal edging or rounded evergreen accents, or in pots and planters. It can be trimmed too, into super-tight, compact low hedges and globes.
Plant the Emerald Knoll Korean Boxwood in full sun or partial shade – it grows in a wide range of light conditions. Richer, moist but well-drained soil is best, but it will tolerate poorer soils. Generally it is unlikely to have pest or disease problems, and left alone by deer and rabbits. Trim in late spring if you want to, but it will always look great even if you never touch it with clippers.
When choosing boxwood, the differences are subtle or even invisible in young plants, but become much more obvious when they mature. Even more so if you want to let them grow naturally, without the chore of clipping, but you want them to remain compact and low. If ‘compact and low’ is what you are looking for, then here it is. The Emerald Knoll Korean Boxwood forms a low mound, broader than tall, topping out at no more than 2 feet, but spreading to double that. For edging and fronting your beds it’s a natural, allowing for wider spacing and therefore reduced cost, and still giving you in a few years a perfect dense green finish to your beds, or along a walkway. As well, the leaves are unusually small and closely packed along the stems, so it looks the perfect miniature. Plus, being a Korean boxwood, it has excellent hardiness, and resistance to winter cold without unsightly bronzing, making it the perfect choice if you garden in colder zones.
The Emerald Knoll Boxwood is a low, mounding evergreen shrub growing 3 to 4 inches a year, and reaching 18 to 24 inches within less than a decade. It has a broad spread, reaching 3 or even 4 feet wide in the same time-frame. It has a dense, twiggy structure and stays bushy and green right to the ground. Untrimmed it has an attractive billowy, mounding form, with flexible branches that don’t easily snap or break when laden with snow or ice. Trimmed (which is entirely optional) it develops a very dense and tight structure, making solid hedges and globes that can be as geometrical and perfect as you want them to be. The small leaves – about ½ inch long, and never more than 1-inch long – are smooth, glossy, rounded and leathery, closely packed along the stems. Their deep-green color is consistent all year round, without any of the typical bronzing and discoloration seen on older types of boxwood in winter. New growth is brighter green, rapidly darkening to a rich and beautiful color that is perfect for framing your flowering plants.
The Emerald Knoll Boxwood is the answer to all your edging needs, forming wonderful informal edges along beds if untrimmed, or easily trimmed into tight, low hedges down as low as 8 inches in you want, and up to 2 feet. With its tiny leaves it looks great either way, and fits just as well into a modern, informal or Asian-themed garden as it does into the classic ‘boxwood-hedges’ look of the most formal garden design. The broad spread means wider spacing is possible for hedges, meaning significant cost-savings can be made. This bush can also be clipped into balls, or left to form natural mounds, ideal for accenting your planting, ending a bed, or filling a gap among existing shrubs. From zone 7 it can be used in planter boxes left outdoors all year round. In colder zones, plant them temporarily in the garden, and re-pot in spring.
The Emerald Knoll Boxwood is a very hardy Korean boxwood, so it is rock-solid in zone 5, and reliable in zone 4 too, although there some tip-burn or a few brown leaves are possible. In zone 4 water deeply just before the ground freezes, mulch use anti-desiccant spray if necessary.
Whether in full sun or partial shade, the Emerald Knoll Boxwood will thrive. It even tolerates shade with just a couple of hours of sun each day, but growth could be a little thinner and more open. It grows in just about any well-drained soil, doing best in richer soils that are reasonably moist, so some preparation of the planting area with organic material is valuable.
Although boxwood can be bothered by some pests or diseases, the Emerald Knoll Korean Boxwood is more reliable than many others, and generally stays healthy and clean. It isn’t bothered by either deer or rabbits, so once established it can be left to take care of itself. Although perfect for natural, untrimmed growth, it does help to trim young plants once a year for the first few years, as this builds dense internal structure. After that no further trimming is needed, unless you want that formal look, or a Japanese ‘cloud pruning’ style. The ideal time to trim is in late spring, once the new growth has darkened in color. You can also trim in early summer and in early fall if needed, but avoid fall trimming in colder zones, if you can.
The Korean Boxwood, Buxus sinica var. insularis, is still sometimes called by its older name of Buxus microphylla var. koreana. It is more cold-hardy and generally tougher than the English boxwood, and highly recommended for American gardens in both cold and hot zones. The Emerald Knoll Boxwood was found in 1991 by Robert and Lisa Head, of Head’s Select Inc., a plant breeding nursery in Seneca, South Carolina. It was a unique branch growing on a variety called Kingsville Dwarf. It produced plants that were faster-growing, as well as more spreading and billowy than the parent, and so less prone to pests and diseases or winter breakage. They named the new plant RLH-BI, and it was originally distributed from 2012 by Greenleaf Nursery of Oklahoma, with the trademarked name Emerald Knoll® as part of their Garden Debut® collection. However in 2020 the trademark was canceled, meaning that today we can either call it RLH-BI Korean Boxwood, or use Emerald Knoll as a common name, which we have chosen to do. Some experts believe it may be identical to an earlier existing variety called Tide Hill, which future DNA studies may confirm.
If you love mounds of boxwood, but hate trimming, or simply don’t have the time, then the Emerald Knoll Boxwood is for you. Enjoy a great look with broad, spreading, dense plants – but no trimming. Whether you want accents, edging or potted plants, and also if you do want low trimmed hedges, this bush is a top choice, especially in areas with cold, snowy winters. Order now, as this variety remains rare and hard to find, so take advantage of their limited availability.