Please advise on what plants – shrubs, flowers and groundcovers are recommended for planting under a mature white pine.
The mature Eastern White Pine, Pinus strobus, is a majestic sight in the landscape. What could be more appropriate as Ontario’s provincial tree! However, in an urban garden it can be a challenge to find plants that will grow and thrive under its dense canopy. Pine trees grow best in acidic soil, and indeed, as their needles drop this soil acidity is perpetuated. In addition there is a slight allelopathic effect (negative effect on other plant species) from the chemicals produced by the shallow roots of the white pine. Any plants underneath will need to be able to tolerate a lower pH level, dry and shady conditions as well as potentially poor soil conditions. This can be a tall order.
Groundcovers you might investigate include common bugleweed, Ajuga reptans, a creeping rhizomatous perennial that spreads by stolons. Ajuga tolerates acidic soil, dry conditions and shade. Some attractive cultivars are ‘Multicolour’, ‘Burgundy Glow’ and ‘Metallica Crispa’. Bugleweed can invade lawns, but under your white pine it should be possible to control its spread. Galium odoratum, sweet woodruff, is another creeping perennial suitable for shaded woodland conditions: its glossy emerald green leaves and scented white star-shaped flowers make an attractive carpet. It is less tolerant of dry conditions. Also needing regular moisture is creeping wintergreen, Gaultheria procumbens, another evergreen perennial that will tolerate shade and acidic soil.
Azaleas and rhododendrons thrive in the acidic soil that is found under pine trees. Shrubs such as Arctostaphylos uva-ursi, bearberry, or Fothergilla, with its pretty bottlebrush flowers are also possibilities. Perennial plants that will tolerate the conditions under a white pine include Canadian wild ginger, Asarum canadense and columbine (Aquilegia canadensis).
It is no accident that many of these suggestions are native plants that occur in woodland settings. A visit to a native plant nursery (or its website) may give you more ideas. You may be interested in checking out the Toronto Master Gardener’s guides to drought-tolerant and shade-loving perennials:
Very best of luck with your plantings!