Sloping gardens

(Question)

Eight years ago, built garden to avoid mowing steep-sloping, east-facing front yard. Sun is an issue. I planted Kitten’s Eye iris, daylilies, siberian iris and Brilliant sedum, along with some creeping blue-flowered veronica, variegated hosta and ground phlox at bottom to “hold” the soil on hillside and minimize erosion (have also shored up with some large rocks to this end). The plants mentioned above and rocks have worked like a charm, as have tall phlox added later. But other early plantings, such as coral bells, peach balloon flower, flowering sage, tall speedwell and persian bellflower, have lost out to competition and changing (declining) sunlight, as neighbouring trees grew and competing plants matured. Now wondering what else I could grow here, particularly flowering plants that will grow low to ground rather than getting too big and tall and shading/crowding adjacent plants. Maybe I just have to be more ruthless about dividing and controlling the plants I already have? I put a white compact japanese anemone near bottom of hill to fill a space and add fall interest. It is growing into a clump and blooming nicely in its second year there, but starts blooming at end of September, thus far. Doesn’t leave much time for it to show its stuff. Should I move it, or give it a couple more years to mature and gather steam? I notice a lot of neighbours also have hillside gardens, so some articles on how to plant and maintain slopes, especially with flowering plants with strong root systems rather than groundcovers, might be useful to many Torontonians.

(Answer)

It is hard gardening on a slope but is very rewarding when all your efforts pay off.  This type of gardening comes with some unique challenges such as:

  1. How to stop soil erosion?  Answer – planting material with strong deep roots.
  2. How to get enough water to the planting material?  Answer – some form of irrigation such as drip lines.
  3. If the slope is greater than 30 degrees, is some form of terracing needed?  Answer – yes, the steeper the slope the more terracing/hardscaping is advisable.

The above being said, there are many planting schemes to help with creating a safe, sustainable and aesthetically pleasing garden that won’t have you working every minute of your spare time.  See below for a few suggestions which you can intermix to great effect.

Trees & shrubs to add dimension, shade, interest, stop evaporation and encourage birds & wildlife – deeper rooted to stabilize soil:  Acer palmatum (Japanese maples), Euonymus alatus (burning bush), Symphoricarpos (snowberry), Forsythia ‘Arnold Dwarf’ (dwarf forsythia), Hydrangea, Boxwood, Cotoneaster, Creeping Juniper.

Perennials to add colour and texture throughout the season – Hellebore, Lamium (deadnettle), Echinacea (coneflower), Euphorbia (spurges), Phlox, Cerastium tomentosum (snow-in-summer), Pulmonaria (lungworth), Salvia (Russian sage), Rudbeckia hirta (black-eyed Susan), Ferns.

Ground covers:  Ajuga (bugleweed), Sempervivum tectorum (hens & chicks), Cotula coronopifolia (brass buttons), Thyme, Pachysandra terminalis (Japanese spurge).

Grasses:  Red Fescue, Little Bluestem, Switchgrass.

Bulbs, tubers, corms & rhizomes: Crocus, Iris (bearded and Siberian), Camassia, Allium, Hemerocallis (daylilies), Narcissus (daffodils).

Roses: Climbing, Carpet and Rugosa.

All of these options, along with some prudent thinning and pruning of what you already have, should help you grow a wonderful garden.

Hope this helps