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The What and How of Rock Gardens

The What and How of Rock Gardens

Rock gardening originates from England, and conjures an image of textured, ruddy rocks intertwined with plants, climbing their way down the sloping elevation. However, the slope itself can be naturally occurring or constructed, just as the stones can be natural outcroppings or brought in. Generally, the rocks hold the embankment in place and serve as a backdrop to the individual character of each plant. The alternative to this “natural” look, when a change in elevation is the case, is constructing retaining walls and/or terraces.

What Kind of Rocks to Use

  • Make your rock garden look as natural as possible.
  • Larger stones are preferable. A lot of small rocks can look messy and ineffective.
  • Try to work with stone from your area that will harmonize with your architecture and hard landscaping.
  • All the rocks should be of the same general kind rather than a geological collection.

granite stones rock bed garden

  • Novelty rocks simply grab too much attention.
  • Weathered stone that’s porous is ideal. Limestone, for example, absorbs moisture and acts as a buffer during dry spells.
  • Non-porous rocks such as Granite can cause rapid drying of the surrounding soil system because it doesn’t absorb moisture.
  • Avoid all soft and scaly rock, shale, and un-weathered sandstone.

How to Build

  • When positioning stones on a slope try to imagine how they would look in their natural state.
  • Plan out where the plant “pockets” will go. Create space where the roots can reach down to the soil.
  • Also, vary the size of the planting pockets between the rocks to accommodate the various mature diameters of your favourite plants and to reinforce the idea of randomness.
  • Start with the largest rocks, and work them in with smaller ones.
  • Avoid perfect symmetry! Try for a careful randomness.
  • Arrange each rock so its best “face” will show well and then dig it a third to a half into the incline so it looks like an outcropping not a stone sitting awkwardly on top of the soil.
  • Slope the stone back to direct rain towards plant roots.
  • Rock garden plants grow best in well-drained soil. After placing the stones, add a mixture of perlite, vermiculite, and peat moss into the planting pockets.
  • Avoid rich soil or clay that won’t drain.

clay puddle

  • A sprinkling of lime is recommended in areas with acid-type soils. Two plant exceptions are Lithodora and Gentians that prefer the acidic soil condition.
  • If your rock garden is going to be more than 2.5m(8′) wide, incorporate a path and/or steps through it so you can maintain plants, weed, and clean up in the fall.

What to Plant

  • The choice of plant material depends on lighting conditions.
  • Proportion is paramount in relation to the size of the rocks or boulders you’re using.
  • For large scale landscape rocks with approximately 100 cm (40″) between them, you can work successfully with such slow growing specimens as:
    • Rose Daphne
    • Nest Spruce
    • Dwarf Alberta Spruce
    • Boxwood
    • Little Giant Globe Cedar
    • Goldmound and Goldflame Spirea
    • Dwarf Hinoki False Cypress
    • Jeddeloh Dwarf Hemlock
    • Blue Star and Goldstar Juniper
    • Nikko Slender Deutzia
    • Dwarf Mugho Pine
    • Sunburst Hypericum
    • Dwarf Balsam Fir
    • Red Ace
    • Yellow Gem
    • Abbotswood Potentilla
  • These cascading plants will work well with the above choices:
    • Dwarf Japanese Garden
    • Blue Chip and Prince of Wales Juniper
    • Siberian Cypress
    • Rockspray Cotoneaster
    • Stephanandra
    • Wintercreeper Euonymus
    • Weeping Japanese Maple
  • Mix evergreen with deciduous and vertical with horizontal to create a tapestry of textures worthy of attention all year.
  • For a smaller scale use small stones, miniature bulbs, annuals, and perennials to provide flowering interest for many months.

succulent rock garden

  • Start planning for spring by planting bulbs:
    • Snowdrops
    • Winter Aconites
    • Glory of the Snow
    • Crocus
    • Iris reticulata
    • Puschkinia
    • Scilla
    • Dwarf Daffodils
    • Greigii and Kaufmanniana Tulips
  • For April/May there are many low-growing perennials that would add bursts of colour like:
    • Primula
    • Basket-of- Gold
    • Pasqueflower
    • Candytuft
    • Rock Cress
    • Creeping Phlox
    • Dwarf Iris
    • Thrift
  • The next perennials to bloom are:
    • Woolly Yarrow
    • Mt. Atlas Daisy
    • Carpathian and Serbian Bellflowers
    • Creeping Speedwell
    • Yellow Ice Plant
    • Dwarf Dianthus
    • Saxifrage
  • For summer you can intersperse annuals that will reliably bloom all summer:
    • Dahlberg and Swan River Daisy
    • Alyssum
    • Lobelia
    • Portulaca
    • Nierembergia
  • Summer flowering perennials include:
    •  Sun Rose
    • Coral Bells
    • St. John’s-Wort
    • Blue Flax
    • Stonecrop
  • For a low mat effect, plant Creeping Thyme or Scotch and Irish Moss.
  • For interesting foliage colour try:
    • Silver Mound or Silver Brocade Artemisia
    • Bright yellow Creeping Jenny
    • Black Lilyturf
    • Variegated Liriope
    • Steel blue Donkey-tail Spurge
    • Burgundy Bertram Anderson or Vera Jameson Stonecrop
    • Elijah Blue Fescue

Alpine Plants

“Rock Garden” and “Alpine” plants are used interchangeably but a true Alpine grows above the tree line in mountainous regions.

  • Alpine perennials have a dwarf habit, bloom profusely, and prefer a well-drained, gritty soil. These include:
    • Gentians
    • Saxifrage
    • Alpine Lady’s Mantle
    • Stonecrop
    • Edelweiss
    • Alpine Columbine
    • Lewisia
    • Alpine Poppy
    • Arctic Campion
    • Alpine Aster.

hens-and-chicks-succulent-207616_1280Trough Gardens

If you have limited space you can create a miniature rock garden in a special planting container called a trough.

  • A trough is a heavy rectangular tray with drainage holes that’s elevated on concrete blocks and filled with a layer of stone at the bottom and quick-draining, gritty soil.
  • A standard soil mix for a trough is 20% compost, 30% loam, and 50% fine gravel/sand.
  • In a smaller trough, you can try planting succulent perennials like Stonecrops, Hens and Chicks, and Saxifrage with interesting rocks and gravel to finish the top.
  • Very slow-growing evergreens can be used in larger troughs. Once planted keep the trough free of weeds and water as needed (every day or every other day in hot weather).
  • Troughs with winter hardy plants can stay where they are or be set on the ground in December and covered with evergreen boughs.