Marilyn Clark offers tips on creating a beautiful rock garden to enjoy year round
Winter is here. What is a gardener to do? I’m dreaming up plans for next year, hoping to renovate my rock garden. I built it many years ago with very little knowledge, and primarily as a place to put the rocks I dug up trying to plant trees! Since joining the North American Rock Garden Society, I’ve been exposed to numerous examples, and learned how perfect they are for our Central Oregon Climate. So, what is a rock garden and why are they so good for Central Oregon?
A rock garden is a garden planned around the use of rocks as a primary feature. These gardens can be small or very large, flat or on a hillside, and are generally low maintenance. (No mowing!) The idea is to use genuine mineral stone in a natural manner, incorporating the plants in a complimentary design.
Here are some considerations:
Choice of rocks. It is generally best to select rocks that are native to your area because they look more natural. Plus, transportation costs are greater with more distance! The geology of central Oregon is quite diverse and includes lava rocks, basalt columns, red cinder, volcanic ash flow tuff (as at Smith Rock), volcanic rhyolite, Cline Butte pink gravel, and river rock. There are numerous choices carried by local quarries, stone yards or large landscape-organic products suppliers. Most can be purchased by the yard. Large stones/boulders are available by the pallet.
Design style. What type of rock garden appeals to you? It may surprise you to learn there are many themes you can choose from. A dry creek bed, a crevice garden, an alpine garden, a rocky hillside garden, a cactus garden or even a Japanese Zen Garden are all possible in the high desert, providing you have the right soil, sun — shade, or shelter considerations included in your design. Work to take advantage of the attributes of the sight. Example: A west facing slope in full sun with sandy/loamy soil is perfect for a cactus garden. Accented with large native pink rhyolite stones and mulched with pink gravel, it would be quite unique and very water-wise and fire-wise. Numerous hardy cacti are available, ranging from ball cactus to prickly pear to cholla. Alternatively, an alpine garden with low-growing plants tucked into a semi-shady spot amongst small conifers and grasses might appeal to you. Gentians, Indian paintbrush, and plumbago make a colorful combination in spring. Crevice gardens are a relatively new theme, taking advantage of deeply seated rocks placed vertically to encourage deep root growth. Small plantings emerge between the rocks and are sheltered by them. Be sure to consider the style of your home and chose a garden style to compliment your home and overall setting. Unless you are planning a Zen Garden, rock gardens are supposed to look random, even the plants. No straight lines or symmetry in plantings.
Stone placement. A pleasing rock garden is one in which the placement achieves a natural look. The stones appear as though they are an exposed portion of a larger underground stone. Imagine the stone as a tip of the iceberg. Don’t just sit them on top of the ground. The height of the stones and general terrain should vary. Stones should be placed in random groupings. The stones should relate to one another as if the bedrock foundation has been exposed by erosion. Lastly, consider the size of your lot, e.g., large stones in a small yard can be overwhelming.
An aged look is more natural. Stone faces can be sharp and shiny or weathered, worn and aged wearing moss or lichen. An aged look is generally more appealing. Moss appears natural in shaded areas. Surprisingly, lichen is very adaptable in central Oregon and some varieties even survive in full sun. I was fortunate to find both on our property. If you wish to achieve the look, find some patches of moss or lichen thriving in similar conditions to that which you are creating and apply a mixture as below. For lichen, fill a spray bottle with milk, collect two teaspoons of lichen flakes, and blend by shaking gently. Spray the mixture on the rocks, keeping it moist until they take hold. For moss, place two tablespoons of ground moss pieces to 2 cups of yogurt and 4 ounces of potters’ clay mixed to a creamy consistency. This mixture can be painted on the rocks to ‘seed’ the moss. Keep it moist by spritzing it daily. It only takes a few weeks to achieve an aged look.
Soil types. After the foundational rocks are placed, the soil can be loaded next. Most of us have very little soil, so must purchase topsoil or bagged soil mix to create our rock ‘islands’ and artificial slopes. The soil type should be determined by the type of plants desired. Examples: Typical alpine garden plants require a fairly porous, rocky soil. Central Oregon soil is most commonly a sandy loam, which drains well and lends itself well to a succulent and cactus garden. Most traditional garden plants do well in a quality garden soil blended with compost and other organic amendments.
Plant Selection. Should be determined by the style of garden you wish to achieve and be compatible with the sun/shade of the site and soil mixture. Unless your microclimate is special, look for plants with a cold tolerance of zone 5 or less. Read the plant label for the requirements of the plants you desire and group plants with similar needs. It’s easier when they share watering requirements, pH, etc. Rock garden plants don’t have to be boring. New varieties and flower colors are developed every year.
Hardy Plants for Central Oregon. These are relatively short or compact and have done well in my yard, although some are less tolerant of deer foraging.
Creeping Germander (Teucrium)
Hens & Chicks (Sempervivum)
Hummingbird Mint (Hyssop)
Ice Plant (Delosperma)
Sea Thrift (Armeria)
Have fun. Place plants adjacent to the rocks, tuck them in to niches or allow them to spill over the rocks as they would in nature.
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