Ravine gardening

Pity the poor ravine people. There they are on the edge of great things just waiting to be waved home. Waiting to turn their degraded urban ravines into woodland wonderlands. Oh how they wish their trees were majestic oaks rather than brutish Norway maples. That the shrubs were bewitching witch hazels rather than beetle bitten European viburnums. And at their feet, instead of stinky garlic mustard, how they long for a carpet of mayapple and dog tooth violet.

Ravines are magical places but so vulnerable. Go ahead and garden there but with a light hand and a conscience.

Carl Rothfels is the field botanist at the Royal Botanical Gardens and has walked many furlongs of shady slopes.

"Many ravines are ecologically damaged, they are subject to erosion, sudden floods, invasive species, and compaction from heavy human contact." Then it's no surprise according to Carl that the vulnerable native wildflowers are the first to go under such pressure.

Trilliums, bloodroot, and foamflowers get bowled over by escapees from the garden such as periwinkle, honeysuckle and wintercreeper, Euonymus fortunei. Aggressive Norway maples invade ravines and turn the soil dry as dust with their heavy feeding roots.

This altered environment also creates the perfect home for an unwanted bully-garlic mustard. If you notice your ravine is carpeted by plants with heart-shaped leaves, white flowers in May, and gives off the aroma of garlic when crushed, you have the mustard menace.

"Garlic mustard has a five to seven year seed bank," says Rothfels. "The only control on a small scale is hand pulling, but you have to remain committed to it."

In fact, if you want to garden in a ravine, proceeding on the "small scale" is just about the best overall advice you can follow.

First of all, if you want to educate yourself on invasive plants, look to the Ecology and Management of Invasive Plants Program. The program is affiliated with Cornell University in New York, and provides an easy search engine to look up alien species.

Then if you want to introduce better plants into the ravine, take small steps.

"You don't want to dig up large sections of the ravine to plant, and expose bare soil to erosion," says Darren Schmahl, garden designer and owner of the Copper Leaf Garden Store in Jordan Village, ON.

He also advises to work with the native soil, even if it's thin and dry, rather than trying to make large-scale changes to the site.

Carl Rothfels agrees, "From a natural lands perspective, there is no such thing as bad soil." But by being a good steward to the ravine, "reducing erosion, compaction and presence of invasive species," Rothfels says growing conditions should improve for a wider variety of plants.

Erosion can be controlled by mulching with a one to two inch layer of shredded bark, or using fallen leaves, or leaf mould to cover exposed soil. In other words don't make your ravine unnaturally pristine.

Compaction from the tromping of human feet can be managed by creating paths and using them. At one of the Royal Botanical Gardens ravine locations generous woodchip paths, graced with the occasional bench creates a serene and contemplative atmosphere.

Choosing the right plant for the right place will always minimize losses as well. In the dry soil under trees consider planting Canada ginger Asarum canadense, bloodroot Sanguinaria canadensis, meadowrue, Thalictrum dioicum or Canada violets, Viola canadensis.

If you're lucky enough to have wet areas in your ravine another world of fine plants, many native, awaits you. Marsh marigold Caltha palustris, many types of ferns and Jack-in-the-pulpit, Arisaema triphyllum, are treasures for this setting.

In damp areas watch out though for a serious invader, the handsome but too aggressive European grass called phragmites. The grass, with big plumes at this time of year, runs rampant in marshlands, roadside ditches, just about anywhere it can get established. And once it does it creates a monoculture and crowds out other species. In-depth information on native plants is available from the North American Native Plants Society, or by searching out the books of Toronto author Lorraine Johnson.

In my own garden, which is not near a ravine but on a plain old slope, erosion control was a serious concern. Our first priority was to cover up bare soil. We planted annual rye grass in the fall, covered it with burlap, crisscrossed the hill with twine tied to stakes, and let the grass germinate through the burlap. The fabric helped protect the soil on the very steep slope from high winds and rain that would have certainly flushed lots of soil to the bottom.

The following spring, we removed the burlap and slowly began to replace the rye grass with perennials, shrubs and trees.

So on slopes in ravines, or right out in the open, proceed with caution, plan carefully, and enjoy the small successes.