Here we go again, About Evergreens, Trees & Shrubs in Containers!
by Art Drysdale
by Art Drysdale


Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at

March 15, 2009

Above, a photo of my second-floor balcony in Toronto--it was the cover photo on my book Gardening Off The Ground; and an old shot of a typical Japanese yew (Taxus cuspidata)in a Reff patio pot sold by Sheridan Nurseries in the 60-70s. These are not hardy in containers under most conditions in Ontario. Below, weeping peashrub (Caragana arborescens ‘Pendula’)--one of the absolute hardiest shrubs for container planting; followed by a close-up of the fine flowers and fern-like foliage of the closely related cut-leaf peashub (Caragana arborescens ‘Lorbergii’); and two trees that are reasonably hardy in containers: littleleaf linden (Tilia cordata) good only in Toronto; and hardy poplars, e.g. Carolina poplar (Populus canadensis ‘Eugenei’) growing in a raised container in Regina, Saskatchewan (zone 2b). Author photos.

This week, yet another question that is basically answered in my book Gardening Off The Ground. It comes from Jim Chaput in Guelph, Ontario. “Hi Art; hope this message finds you well ... I live in Guelph, Ontario and my mom and dad in London, Ontario. We are both seeking information about what evergreen coniferous shrubs (spruce, yew, cedar, etc.) might be suitable for an apartment balcony in our area? Also what about deciduous shrubs or trees like euonymus or a pyramidal oak? The main question is what kind of pot is required and is there a chance these might survive the winter? Thanks for your guidance.”

Unfortunately (for both of us) the book is currently out of print, although I am slowly making headway toward hav-ing it available as an e-book. Your questions are all answered in one particular chapter--Trees and Shrubs for Your Containers. Here is an excerpt that may help.

“When it was built in the early 1960s, the fifth-floor balcony of a Toronto office building included two medium-sized plant containers. Because the balcony faced east and Japanese yews grow well in shade, nurserymen recommended the traditional yew as a satisfactory evergreen for the containers. But the trees could not withstand Winters, and had to be replaced each Spring.

“The building managers finally grew tired of the continual expense and labour, and asked me what I thought they should plant instead. They specified a plant about 90 cm (3') tall that would still be alive after the gruelling Winter. I explained that I was certain it was more important to plant an extremely hardy small tree or shrub than one tolerant of the shady easterly exposure. I also said that in my opinion the amount of light available five storeys up on an easterly exposure would probably be almost as much as is normally found facing west at ground level.

“The building managers accepted my advice and decided that they did not necessarily need evergreens, since the balcony was not used during the Winter. Jointly, we agreed that flowers in Spring or early Summer would be more valuable, and for each container chose a weeping peashrub (Caragana arborescens ‘Pendula’), a small-leaved shrub whose branches hang down from a 90 cm - 1.2 m (36-48") stem. As the plant matures, the number of branches in-creases but its basic height does not, because of its weeping habit. The plant is extremely hardy, growing well in zones 2 to 9. It is a close relative of the Siberian peashrub (Caragana arborescens), well known on the prairies as a hedgerow or windbreak. Attractive bright-yellow flowers resembling those of sweet peas appear in early Summer, followed by small seed pods. The two trees remained in the same containers, on that fifth-floor balcony for over a decade!

“Before continuing this chapter, I should emphasize that there has been no basic research into growing trees and shrubs in containers that are above-ground, and on balconies, over cold Winters. You might not be able to duplicate exactly the results of some of the experiments I describe, which have taken place mainly in southern Ontario (zones 5 and 6). Your success will depend a good deal on your climate. Toronto, for example, is milder than Montreal and a great deal milder than Ottawa.”

Here is a further excerpt that is about specific recommendations of evergreens, and then one about how to plant ever-greens in containers.

“Of the other taller evergreens I suggest you might consider for container or floor garden planting on a balcony, two are junipers —named Wichita blue (Juniperus scopulorum ‘Wichita Blue’ and blue arrow (Juniperus virginiana ‘Blue Arrow’). Both are conical, but blue arrow is the thinner of the two. I have a hedge of Wichita blue in my garden that is a delight 12 months a year!

“Four well-known spruce trees, two of which are commonly used for timber, are extremely hardy and suitable for container growing. These are the Norway spruce (Picea abies), white spruce (Picea glauca), Colorado spruce (Picea pungens), and Hoopsi blue spruce (Picea pungens ‘Hoopsi’). All of these grow to heights of 15 to 21 metres (50-70') ornamentally, and even taller in the forest, but if planted in containers when they are only 60-90 cm (2-3') high, will remain under 1.5 m (5') for many years.

“The white spruce has medium-green, somewhat bluish needles just slightly longer than one centimetre (½"); the Norway’s dark-green needles are similar but its growth habit is more picturesque; the Colorado’s needles are twice as long and are green in colour, while the Hoopsi has long, light-blue needles that retain their blue tinge throughout the year.

“One other tall, slow-growing evergreen that is hardy and suited to pots is the Swiss stone pine (Pinus cembra). It grows in a narrow column that makes an ideal centre for a large container of flowers, but again, do not crowd it with vigorous annuals.

“In the spreading evergreens section, I mentioned two varieties of Thuja which are generally considered cedars, though their proper common name is arborvitae. There are several tall-growing arborvitae or cedars that will grow well in containers. Likely the three hardiest and best are the Brandon cedar (Thuja occidentalis ‘Brandon’), emerald cedar (Thuja occidentalis ‘Emerald’), and DeGroot’s spire cedar (Thuja occidentalis ‘DeGroot’s Spire’). The latter is the narrowest—achieving a column diameter of no more than 25 cm (10"). It was a selection made by a late friend of mine, Constant DeGroot, who was chief propagator at Sheridan Nurseries for almost 40 years.

“Finally, a broadleaf evergreen that may be familiar to you from ground-level gardens—the Spanish bayonet (Yucca glauca) is actually native to Alberta! This is a plant that looks as if it should be growing in a desert—but it will grow in containers if they are in full sun daily. Yucca prefer sandy soil and in a few years will provide tall spikes of creamy-white flowers annually in early July.

“Planting Evergreens in Containers. All these evergreens need a minimum soil depth of 30 cm (12"), though a depth of 40 cm (16") is desirable. You should plant them in floor-level pots or floor gardens. Evergreens all like plenty of organic matter, so either a Cornell mix or ¼ each of garden loam, Canadian sphagnum peat moss (or Coir), other organic material such as leaf mould or cattle manure, and sand.

“Ideally, evergreens should be planted between the end of April and early June, or from the beginning of July until mid month, provided the temperature is not consistently over 24ºC/75ºF. The best time to plant is early May. Even though your garden supply dealer may tell you that evergreens can be planted in September, before buying make certain the supplier is willing to replace them should they die during the Winter. Some garden supply dealers have a policy of not extending their normal guarantee to plants, particularly evergreens, if they are to be planted in containers.”

Final point, if you re interested in further information, and suggestions of the hardiest trees, shrubs and evergreens, I could likely make the entire available to you by e-mail but I would have to make a charge.

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