Sizing up Mugo Pine
by Anne Pink
Many growers and retailers find Pinus mugo (mugo pine) possesses many appealing qualities. The plant is attractive, adaptable, available, inexpensive to produce, easy to sell and relatively free of pests. It is also extremely cold-hardy (to Zone 2); since evergreens do not go dormant and are often stressed in winter, the introduction of a hardy plant can have a big impact on consumers. Yet, mugo pine is not a favored selection for homeowners due to its unpredictable growth rate, size and shape. Dr. Michael Dirr, professor of horticulture at the University of Georgia, Athens states he has seen specimens ranging from 3 feet tall to nearly 45 feet tall.
Mugo Pine's incredible, yet frustrating, variation is primarily the result of its large native range. Plants with large territories tend to have greater nature/variation than plants with small ranges because they must be flexible enough to adapt to different climactic conditions to survive. Mugo pine's native range is western Europe, eastern Europe, southern Europe, and western Asia. Such a broad range requires a chameleonlike ability to adapt to different situations, which is why specimens of every size, shape and description can be found. Although there are many kinds of cultivated and naturally growing types, all are commonly known as mugo pine.
The objective of any growing operation is to get as many plants to salable size and into the market as quickly as possible. Unfortunately, this good business sense favors fast-growing plants, which typically have long needles and a more open habit; the seed-grown, naturally occurring P. mugo var. pumilio has dominated the market because it is inexpensive to produce and sell, and it grows quickly. The slow-growing specimens with short needles and dense, compact habits frequently end up composting in a discard pile.
It would be wonderful to walk through a block of identical 5-gallon P. mugo var. pumilio and predict which plants were going to be rangy and open
and which ones were going to be dense and compact. That way, plants could be sorted and arranged, and everyone could just help themselves to the kind they wanted. A growing number of nursery professionals believe the time has come to retire P. Mugo var. pumilio and find a dependable replacement. The problem, however, is not a lack of good mugo pine specimens, but finding affordable and dependable methods of mass producing them.
Although gardening is the nation's No. 1 hobby, most homeowners do not have enough time to devote to a high-maintenance landscape. Nursery professionals stated selecting plants for specific characteristics, such as growth rate, size and habit. By harvesting cuttings from a parent plant and grafting them onto understock, growers are able to provide consumers with dependable mugo pine varieties that grow to predetermined sizes at predictable rates.
The advantage to consumers was immediately evident - varieties propagated vegetatively could be placed in foundation plantings or shrub borders and would not overwhelm buildings or neighboring plants. These same cultivars could be used with confidence in symmetrical designs - something that could not be done with wildly inconsistent, seed-grown plants. However, seed-grown cultivars still had the edge in sales because they cost far less to produce than the grafted cultivars. Although customers were attracted to the dependability new cultivars promised, the cost difference was so great, the most expensive clones couldn't compete and sales remained relatively low.
Then Paul Halladin, head propagator at Iseli Nursery, Inc., Boring, OR, developed new production techniques using self-rooted cuttings instead of grafting. This process cuts costs significantly and gives the once-costly dwarf varieties a chance to compete with the seed-grown pumilio types - a real benefit to consumers. Because mugo pines with short needles root quite readily, the innovative process works well on compact, shrubby forms of the pine. Iseli Nursery offers about 10 cultivars produced from rooted-cuttings. Let's take a look at what some of these selections have to offer.
Rooting for the Good Guys. Unlike the seed-grown types, many high-quality cloned varieties of mugo pine on the market do not require pruning or candling to maintain a respectable size and shape. Most of these varieties bear short needles; have a dense, compact habit; and are typically low-mounded to globose in form. The P. mugo cultivars 'Mops,' 'Sherwood Compact' and 'Slowmound' are all excellent alternatives to pumilio types. 'Mops' is a dense globe with straight, green needles. Over a long period of time it will reach a size of about 2 to 3 feet tall and just as wide. 'Sherwood Compact' has small, green needles and is a fine choice for foundation plantings since it slowly grows into a globe of 3 feet to 4 feet tall with an equal spread. As its name suggests, 'Slowmound' has a neat, mounded outline and slow growth. It reaches approximately 3 feet in height and spread.
Smaller still is 'Donna's Mini.' This plant is a dwarf and has an average needle length of just five-eights of an inch. This cultivar is best used in rock gardens and troughs where its diminutive size (2 feet tall and wide) is in correct scale. Its annual growth rate is almost imperceptible. Yet another variety, P. mugo 'White Bud,' differs from the other dwarf forms in appearance, but not in size. Dense and compact, it grows 3 feet to 4 feet in height and spread. This handsome plant's winter buds have an attractive, white, waxy coating all winter, giving the plant a wonderful frosty look.
Although gardeners delight in miniature and pincushion varieties, there are landscape situations that call for a more substantial presence. Here, too, vegetative propagation has provided the solution. Two recent introductions give designers and homeowners the opportunity to select a plant of grander proportions. P. mugo 'Big Tuna' has a bushy, upright multi-stemmed habit. It grows taller than it does wide in a somewhat pyramidal shape and is thickly branched from top to bottom. Although a medium-size shrub, 'Big Tuna' still has lush, compact growth, ultimately reaching 6 feet to 8 feet tall and 4 feet to 6 feet wide.
But of all these fine specimens, Iseli Nursery's P. mugo 'Tannenbaum' is the latest rising star. This variety brings a new look to dwarf conifers because it is believed to be the first single-stem tree form of mugo pine being commercially produced and distributed anywhere. "Although another mugo cultivar may not seem glamorous, I'm very excited because this plant fills such a need," says Alan Craig, sales representative for Iseli Nursery. "'Tannenbaum' is a small uniformly shaped tree that really fits into the smaller landscapes of our urban and suburban properties. And to top it all off, it has the extreme hardiness of the species."
Vegetatively propagated and grafted onto inexpensive but compatible P. sylvestris (Scots pine) rootstock, 'Tannenbaum' is an attractive small plant that steadily grows about 8 inches to 10 inches annually and maintains its lower branches - unlike many other pine species. Cone-shaped in youth, the tree becomes more pyramidal with age - the original plant is 25 years old, 12 feet tall and about 6 feet wide at the base.
Unlike the shrubby forms, upright, long-needled forms of mugo pine must still be grafted onto receptive understock because they root slowly with current techniques. Still, compared with high-profile plants like P. cembra (Swiss stone pine), P. peuce (Balkan pine) and P. flexilis (limber pine) - all of which tend to be slow-growing or expensive to produce - 'Tannenbaum' is competitively priced even in its current grafted form. The story of the cultivar is a good example on how plants become new introductions.
A Star is Born. In 1989, Craig was visiting customers in his territory when he met Norm Evers, horticulture instructor and director of South Dakota State Arboretum and McCroy Display Gardens at South Dakota State University (SDSU), Brookings. Evers was continuing research started by his predecessor, Dale Herman. The focus of the study was to monitor the growth characteristics of mugo pines forma wide range of sources and to evaluate characteristics such as dwarfness, compact growth habit, upright growth tendencies, mounded growth, growth rate and needle length.
Herman had obtained a large quantity of mugo pine seed from 46 sites from within the plant's natural range. Twenty to 25 seeds from each source were subsequently set out on a plot of arboretum land. The seedlings were numbered, and their progress was monitored. One surprise of the study was that the seed contained the same wide variability; no matter where it had come from, the seed source appeared to have no bearing on the seedling's growth characteristics whatsoever. Plants form all the sources displayed different characteristics - in other words, procuring seed from a specific source would not produce a crop of all dwarf plants or all uprights.
When the land that housed the project had to be vacated, Evers had space to maintain only about 100 of the most promising looking plants. From that group, Evers and Craig chose three specimens that showed commercial possibility. Cuttings from one of the specimens - a true, single-leader tree - were shipped to Iseli Nursery. These shoots were then grafted onto P. sylvestris rootstock. Evers christened this specimen 'Tannenbaum.'
Current reports from Iseli Nursery indicate public reaction to 'Tannenbaum' is favorable, and sales have been brisk enough to strain production capacity. But is the consumer ready to abandon the tempting bargain price of erratic seed-grown plants in favor of more expensive but reliable cultivars?
Craig believes the time has come to use P. mugo var. pumilio exclusively in breeding programs like the SDSU study and offer dependability and selection to the consumer in the form of rooted cuttings and grafted selections. If Craig is correct, P. mugo var. pumilio will not be replaced with another species, but with it's own cultivars. Evers agrees wholeheartedly: "Why take a chance when you can get exactly what you want?"
That's a question consumers will have to answer.
This article was originally published in American Nurseryman magazine, October 15, 2000. Posted with permission.
Anne Pink is a freelance writer and photographer based in West St. Paul, MN. She is also a member of the Minnesota State Horticultural Society and a certified member of the Minnesota Nursery and Landscape Association and a Master Gardener.