How Big?

On the Growth of Colonizing Woody Ornamentals

Many common woody ornamentals are suckering shrubs capable of spreading indefinitely in the landscape without growing very tall. Therefore, the question of “How tall does it grow?” may not be as significant as “How wide does it grow?” The difficulty in answering either question is a matter of time. Humans are finite creatures; we only grow so tall, then stop and often shrink with age. Woody ornamentals, on the other hand, are capable of nearly infinite growth. If a woody ornamental does not grow each year in some direction, it's dead.

Bushes and shrubs are more height determinate and less width determinate. Rhus typhina – Staghorn Sumac can grow to 25 feet or more with the national champion being 61' in Tallapoosa, AL. Its width, as a colonizing spreading suckering colony can and often does cover square acres to miles. All being the exact same woody plant in-ground just with numerous iterations above ground.

While many shrubs may become arborescent – tree-like with age, technically, they are not trees.

Cornus alternifolia – Pagoda Dogwood, Rosa glauca – Redleaf Rose and Rhus glabra – Smooth Sumac often become arborescent with age. Often, due to diseases and other problems, many of the stems are not long lived, as they are not trees. Therefore, your diligently pruned Pagoda Dogwood must be allowed to produce an occasional sucker or two to continue its life and health.

A tree is defined as a woody plant with a main stem at least 12-15 feet tall and having a distinct crown.

How big does it grow?

I think a more appropriate question is “What's its annual growth rate?” Spreading 1-6 feet per year, Rhus typhina may quickly take over most gardens with its height issues being of little consequence.

How tall does a dwarf conifer grow? ‘Jane Kluis' a wonderful dwarf pine, has an average growth in my Midwest garden of about 3” of height per year. Therefore in 10 years, it will be about 30” taller than it was in 2004. In 100 years it will be 300” taller, discounting my pruning, ‘nature's pruning', diseases, pests and other factors.

It's a tragedy that many labels indicate Picea pungens ‘Fat Albert' Blue Spruce grows to only 10-15 feet. What happens once it gets to 15 feet? Does it stop growing? Nope, it just continues growing past the patronizing information on the labels. After all, I've never met a Fat Albert' that paid any attention to its label.

SO, the next time you shop for any type of woody plant, look for its annual growth rate in height AND width. Discuss its potential for pruning and how pruning may affect flowering, fruit production, health and appearance. MOST non-coniferous shrubs and bushes may be pruned to within 3-12” from the earth, often enhancing the aesthetics of the plant.

The following is a list of colonizing, suckering or spreading shrubs. Please understand, a suckering shrub has unlimited spread, forming a colony or copse in many years. Many of these may live in the hundreds and even into the thousands of years. Many different cultivars are also available for many of the following species, often selected for exhibiting decreased or very limited suckering growth habits. Vines are not included.

Botanical Name - Common Name

Aesculus parviflora Bottlebrush Buckeye

Amelanchier alnifolia Saskatoon Serviceberry

Aronia arbutifolia Red Chokeberry

Aronia melanocarpa Black Chokeberry

Chaenomeles speciosa Common Flowering Quince

Clethra alnifolia Summersweet

Cornus alba Tatarian Dogwood

Cornus racemosa Gray D.

Cornus sanquinea Bloodtwig D.

Cornus sericea Redosier D.

Corylus americanan American Filbert

Corylus avellana European Filbert

Cotoneaster apiculatus Cranberry Cotoneaster

Cotoneaster adpressu Creeping C.

Cotoneaster divaricatus Spreading C.

Cotoneaster horizontalis Rockspray C.

Diervilla spp Diervilla

Euonymus fortunei Wintercreeper Euonymus

Forsythia x intermedia Border Forsythia

Hedera helix Ivy

Hippophae rhamnoides Seabuckthorn

Hydrangea arborescens Smooth Hydranea

Hydrangea quercifolia Oakleaf Hydrangea

Ilex verticillata Winterberry

Juniperus spp Spreading Junipers

Kerria japonica Kerria

Mahonia aquifolium Oregongrapeholly

Microbiota decussata Russian Arborvitae

Myrica pensylvanica Northern Bayberry

Neillia sinensis Chinese Neillia

Nemopanthus mucronatus Mountain Holly

Pachysandra terminalis Japanese Spurge

Physocarpus opulifolius Ninebark

Populus alba White Poplar

Populus tremuloides Quacking Aspen

Prunus americana American Plum

Prunus besseyi Sand Cherry

Prunus virginiana Chokecherry

Ptelea trifoliata Hoptree

Rhodotypos scandens Black Jetbead

Rhus spp Sumac

Rosa carolina Carolina Rose

Rosa rugosa Rugosa Rose

Rosa virginiana Virginia Rose

Rosa setigera Prairie Rose

Rossa spinosissima Scotch Rose

Rubus spp Blackberry, Raspberry

Salix Willow (Many species)

Shepherdia canadensis Russet Buffaloberry

Shepherdia argentea Silver Buffaloberry

Sorbaria sorbifolia Ural Falsespirea

Spiraea latifolia Hardhack Spiraea

Spiraea tomentosa Steeplebush Spiraea

Staphylea trifolia American Bladdernut

Stephanandra incisa Cutleaf Stephanandra

Symphoricarpos spp. Snowberry, Coralberry

Vaccinium spp Bluebery, Cranberry

Viburnum spp Viburnum (Most species)

Xanthorhiza simplicissima Yellowroot

Zanthoxylum americanum Prickly - Ash

How TALL will it grow, may have a limit of 426 feet

Even the biggest trees have limits to their growth. 426 feet may be the tallest any tree could potentially grow according to a recent study reported in NATURE. George Koch and colleagues climbed five of the eight tallest trees in the world and examined their physiology in detail. They found the Californian redwoods are pushing the limits to which water could be raised from the ground to support growth. Coastal Redwoods - Sequoia sempervirens are currently the world champions of height and living more than 2,000 years. In any day, each redwood will consume many thousands of gallons of water. After studying the Redwood's water flow, leaf structure and density, photosynthetic capability and carbon dioxide concentration, they all appear to be converging on a minimum level to which they may grow. The top most leaves are water-stressed according to Professor Koch, a physiological ecologist states, "In essence, the plant is investing a certain amount into those tissues but they're not providing as much return on that investment because of the water stress." Despite conditions at the top, they are still growing at about NINE INCHES per year. Annual varying weather patterns are resulting in greater or lesser annual growth.

Professor Ian Woodward, a plant scientist at Sheffield University, UK, said the work was a fascinating insight into the extreme capabilities of the Redwoods. “When a tree pulls water up through its roots and through its water vessels, the xylem, it has to overcome gravity and friction in the system.” “Eventually, like all continuous tubes of water, when you pull on them hard enough and far enough, they break. Suddenly bubbles of air develop and the whole thing stops.” “Plants have become adept at having very fine xylem that don't break easily and the redwoods have done a great job at this - but they reach their limit at about 120-130m." Prof. Woodward told BBC News Online. (Reference: BBC News Online

SO, now you have it. The tallest that trees may ever grow is 426 feet.

originally published newsletter 2004 V18 #2

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