A multi-tiered approach to incorporating greenery in the landscape is always ideal. Indeed, the typically modest patch of mostly flat area on which the average house sits cries out for multiple layers of interest.
In a mature, roomy landscape, creating an understory layer with newly planted smaller trees has the esthetic benefit of revitalizing a tired leafy backdrop that may be showing signs of age or decay.
In newly developed, treeless suburbs, dwarf trees are the saving grace of impossibly small or irregularly shaped yards.
A layer of shrubs with a diverse mix of perennials and ground cover may seem at first to be a satisfactory concession to the limits of a small space, but this type of design offers small comfort during the winter months when plantings all but disappear from sight.
Philip Ronald of Jeffries Nurseries in Portage la Prairie, Man., has introduced numerous small trees for the landscape, such as Goldspur Amur cherry. A dwarf selection of Amur cherry, it grows to a modest five metres with a relatively narrow width of three metres.
A tiny landscape, though, may not have space to accommodate even a tree of this size.
Top-grafts and tree-forms are a very nice fit for the residential landscape, Ronald says. At most, they may grow as tall as three metres with a narrow width that extends to as little as one metre.
Ronald says many top-grafted trees and tree forms are flowering varieties with potentially larger blooms than other ornamental flowering trees. According to Ronald, the reason for this is that breeders are delving into the shrub world in order to create top-grafts and tree-forms.
The rootstock is the plant with roots that serves as the base. The scion is the plant that is grafted on top of the stock plant. The process during which the two plants unite (grow together) takes both time and skill.
A superb example, Ronald says, is the caragana top-graft whereby an otherwise ground level prostrate caragana is grafted onto a long, straight Common caragana interstem. By raising the cascading fountain of lacy, finely textured green leaves off the ground to obtain a tree-like form with an umbrella effect, breeders have made the Walker caragana top-graft one of the most unique and popular small-space solutions.
Pygmy caragana and Weeping caragana also have arching, pendulous branches. Globe caragana, as the name suggests, has a compact, globe-shaped habit. Each of these varieties has a mature height of approximately one metre and feature small yellow flowers that appear in late spring.
Lilacs are also commonly available as top-grafts. Prolific, showy and fragrant blooms make these lilac lollipops particularly appealing in the landscape. The Dwarf Korean lilac (Syringa meyeri "Palibin") and Miss Kim (Syringa patula) are the most familiar. These grow to a height of two metres with a fairly wide, dense crown (about 1.5 metres) that can sometimes appear disproportionate to the slender stem on which it is supported. Other top-grafted lilacs with a similar height range include French lilac varieties such as Congo, Little Boy Blue and Wedgewood Blue. Tinkerbelle is slightly smaller (1.25 metres) and has wine-red flower buds that open in late spring. Prune after blooming to maintain a manageable shape, taking care to remove suckers at the base of the plant and along the stem.
Less common are top-grafted evergreen varieties that are hardy to our climate. Globe blue spruce topgraft (Picea pungens "Globosa") has a globe-shaped crown with a mature height of 1.5 metres and equal width, and is extremely cold hardy. In this case, a compact rounded evergreen has been trained to grow into a tree-like form and grafted onto a single stem. Its silvery-blue foliage provides a striking accent in the landscape particularly when it is situated in a bed that has a layer of ground-hugging plants that don’t compete with its height.
Double flowering plum topgraft has a taller presence in the landscape, growing to 2.5 metres with a spread of up to two metres and are hardy to zone 2. Double pink blossoms appear in early spring before the foliage leafs out, producing a gorgeous display. Unfortunately, the blooms can be susceptible to a late spring frost.
Top-grafted willow (salix) varieties are becoming more readily available. Undoubtedly beautiful with a weeping crown shape and silvery catkins that have a woolly texture, these are, however, classified as zone 4. Weeping Pussy Willow (Salix caprea "Pendula") is the most familiar, but a particularly tempting variety is the Hakuro Nishiki dappled willow. Available as a lollipop (grafted to a rootstock), the foliage emerges pink in the spring and matures to a variegated creamy white and pale green. The effect is, as you can imagine, perfectly stunning.
Hardiness, though, must always be a consideration in our harsh climate. If you succumb to the charms of a zone 4 plant, choose a protected location and apply a layer of mulch. Willows adapt easily to most conditions, but have a preference for well-drained, moist soil.
There are many hardy tree-form varieties to choose from at local garden centres. Instead of using a grafting process, growers train a shrub to grow like a tree by selecting one major stem and pruning all other branches to ground level. Low growing lateral branches are removed and the crown is shaped. Nursery-grown varieties include hydrangea, physocarpus (ninebark) and viburnum cultivars.
Ronald agrees that the hydrangea tree-form in particular has captivated the interest of homeowners with more and more varieties available each spring, including Limelight, Little lamb, Quickfire and Vanilla strawberry. On young plants, the weight of the heavy blooms can cause branches to sag. When left on the tree, dried, tan-coloured hydrangea blooms provide winter interest.
Physocarpus and viburnum tree-forms offer smaller flowers but have added features such as intriguing bark, berries and fall colour. All of the plants described should be planted in full sun. Staking is essential in the first year.
When only a small space is available for planting, top-grafts and tree-forms provide an interesting option to the homeowner. Keep in mind, Ronald says, that these dwarf specimens won’t have the same longevity as large caliper trees in the landscape. The life span of specialty trees may be in the range of 15 to 20 years. Their ornamental value, however, makes them a good investment.
Ronald’s most important consideration is that the homeowner must be diligent in terms of maintaining top-grafted trees, more so than they would a small deciduous tree. "The scion may not always be as vigorous as the stock or broomstick to which it was grafted," Ronald advises.
When sprouting occurs at the base of the plant, Ronald says it must be controlled. Remove sprouts or suckers as well as any side shoots along the stem as soon as they appear so as to prevent the stock from reverting to a shrub form.
To establish your new plant in the first year, water regularly. In late fall, wrap the trunk with a commercial tree wrap for protection against sun scald. After a heavy snowfall, gently brush the snow off branches.
The Winnipeg premiere of The Gardener, a film by director Sebastian Chabot that tells the story of one of Canada's most legendary gardens, Les Jardins de Quatre-Vents. A special presentation by the Manitoba Master Gardener Association at Cinematique, 100 Arthur St., Feb. 4, 12:30 pm. Tickets are $15. Purchase online at mgmanitoba.com