Rock Garden Design

What to Know, What to Grow: Some Ideas

Rock garden in landscaping: image.
A lot goes into picking suitable plants to grow in a rock garden. Mark Turner/ The Image Bank/Getty Images

Rock garden design may seem simple enough on the face of it, but there is a bit more to it than at first meets the eye. Disabuse yourself of the notion, right away, that it is just a matter of throwing some rocks and plants together! Consult the Q&A that follows for insights regarding selecting and arranging your material, the tools you will need, etc.

What Type of Rock Is It Best to Select?

Are you bringing rocks in from the outside for your rock garden design (as opposed to limiting yourself to rock already on your property)?

If so, you can take advantage of the opportunity presented by starting from scratch (with a clean slate, as it were). You get to choose rocks that are to your liking. You will find this tip on selection especially helpful if you prefer the appearance of aged stone.

Porous, softer rock is better for rock gardens than is harder rock. Harder rocks take longer to acquire the weathered look that you are striving for in the rock garden because they are less receptive to the growth of mosses and lichens. Promoting the weathering of your rocks will give the rock garden a natural look. Weathered stone looks as if it had always been there.

Also, stick to rocks that look the same in texture, color, and form. If you use rocks of similar appearance throughout your rock garden, it will have a more natural look.

All Right, How Do I Achieve That Aged Look to Which You Allude?

Did I catch your attention in talking about the aged look?

Many people prefer it to the appearance of new stone. That is understandable since moss-covered rocks lend a sense of permanence to this landscaping project. So what is the trick to hasten the growth of moss on rocks to achieve a weathered look?

When the rock is brought in from outside the property to construct a rock garden from scratch, it can look out of place.

Its "newness" can stick out like a sore thumb, especially if there are no signs of weathering. Growing moss would solve this weathering problem, and, believe it or not; there's a trick for weathering rocks artificially with rock moss. It's a job that involves strange bedfellows, namely, moss and your kitchen blender:

  1. Bring in some moss that you find growing somewhere -- this will be one of the ingredients of the "recipe." Besides moss, the other ingredients will be about 2 cups of yogurt, and about 4 ounces of potter’s clay to make the moss mixture stick better to the rocks.
  2. Puree the moss, yogurt, and clay until you achieve a creamy consistency.
  3. Pour the moss mixture on your rocks. As the rock moss takes hold in your rock garden, mist it to keep it moist. And voila: you have instant weathering.

Nothing gives rocks that "I have been here for eternity" look quite like rock moss. So make growing moss a priority in your rock garden start-up activities.

Where and How Do I Get the Stone? Are There Any Free Sources?

"If it's free, it's for me" is one of my favorite sayings, and it is certainly applicable to this job (after all, we are talking about one of the most common commodities in the world here: stone).

If you approach the project with an attitude conducive to saving money, there is no reason why it should cost you an arm and a leg.

If you plan on bringing stones in from the outside, the question then becomes one of finding a source. But the answer, to some degree, will depend on how specific and how grand a rock garden design you have in mind. For example, do you envision using a particular type of stone (and no other type will cut it for you)? The answer will also be very different if money is no object (but for how many of us will that be true?). If on the other hand, you have some flexibility and are working within a budget, I have a tip you may find useful.

Let's talk about a free rock source first: cheapskate that I am, I would be embarrassed to start out by telling you how to buy rocks for rock gardens. Go to a construction site. Usually, where there is excavating going on, the stone will turn up. And just as often, those who turn it up are happy to get rid of it, meaning it will be a free rock for you. But ask first.

Having informed you of a free source, I feel less ashamed about telling you now where you can buy stone for rock gardens. Find out if there is a quarry in your area. Quarries can supply you with high-quality stone. Often the beauty of the quarry stone lying there afterward in your rock garden will justify not being free.

How Will I Move Big Rocks Around? Are There Specific Tools for This Job?

Let's say you have a source of rocks on your property (or a consenting neighbor's property). Now the issue is that you need to move them from where they are now to the spot where you wish to begin your rock garden design. What are tools and accessories suggested to make moving the big ones easier?

Since moving rock can be dangerous for those with back problems (and can induce back problems in those formerly free of them), start out by purchasing a back brace. To move the rocks to your future rock garden, there is, of course, the option of bringing in power equipment or winches. But if you want to stick to some basic rock-moving tools and rough it, I would suggest the following tools:

  • A 5-to-6-foot steel bar, which provides better leverage than a mere crowbar (of course, you will need to find a fulcrum to accompany it).
  • A dolly, which is preferable to a wheelbarrow. Since the platform of a dolly is at ground level, you do not have to lift the rocks into it.

What in the Heck is a "Lichen"? And Why Are Lichens Important in Rock Garden Design?

When you hear folks talking about rock garden design, one term that pops up quite a bit is "lichen." Do you wonder what lichens are, exactly, and why they are important in rock garden design? 

Lichens are often spoken of in the same breath as "moss." In fact, a nickname for lichens is "reindeer moss," because they're a food source for reindeer. The "reindeer moss" moniker notwithstanding, a lichen is not a moss at all.

Lichens are compound organisms composed of two or three separate organisms, existing in a symbiotic relationship. The dominant partner is a fungus supplying food by photosynthesis (often through a colony of algae).

Lichens are important in rock gardens and xeriscaping because they are not dependent on a steady supply of water. Lichens survive alternate drying and wetting of their tissues, giving them an advantage in colonizing difficult environments. The Lichen Lovers site has instructions for growing lichens on rocks.

Like mosses, lichens growing on rocks give your rock gardens the desired "weathered" look. Weathering of rocks in a rock garden is central to achieving a natural appearance -- as if the rocks had always been there. In addition to growing on rocks, they can often be found growing on trees, wooden fences, etc.

How Do I Arrange the Stones So As to Create a Natural Look? 

Ah yes, the "natural" look. Everybody wants that, right (I have never heard anybody ask for the "unnatural" look)? So once you have moved stones to the chosen site for your feature, how do you arrange them to achieve a natural rock garden design?

Taking your cue from nature, the idea is to make it appear that the stone in your rock garden is merely the exposed fraction of a massive underground formation. To achieve the look of natural stones, each stone should appear firmly grounded -- as if it were the "tip of the iceberg." Each stone also should appear as if connected to its immediate neighbors, separated only by the crevices in which you will be growing the plants of the rock garden.

As in the natural world, stay away from constrained stone patterns and any too-even distribution, striving instead for a feel of randomness in your rock garden. Have a massive grouping of stones here, a smaller grouping there, and mulched areas in between. The arrangement is crucial to achieving the look of natural stones.

The stones in a rock garden should relate to each other as if they comprised a bedrock formation exposed either by gradual weathering or by more dramatic erosion. Consequently, the major rock faces should point in one direction throughout the rock garden. If the stones are stratified, position the rocks in each grouping so as to have the strata lines all going in the same direction, as they would in most natural stone formations.

What Kind of Soil Will I Need, and How Do I Know the Plants Will Like It?

Here is where we get down to the nitty-gritty. Once the rocks have been set in place to form the foundation for your rock garden design, you should prepare the soil before planting the plants. Also keep in mind the sun requirements of projected plant selections.

As in arranging the rocks in your rock garden, take your cue from nature in arranging the plants. In nature, plants that grow amongst the rocks like well-drained soil. As a general rule, then, you would want to mix sand into the soil that you will be using for planting. But it is best to know the particular requirements of the plants that you will be selecting and to base your soil preparation on that.

Knowing your plants' particular requirements is even more important in preparing your soil to have the proper pH level. Learn ahead of time, while in the process of selecting plants, what kind of soil pH they like, and prepare the soil accordingly. An individual plant choice may prefer acidic or alkaline soil.

Do not mix low-pH plants (that is, acid-loving plants) with high-pH plants (that is, those that prefer an alkaline soil).

Finally, whether your rock garden is in a sunny or shady location will have a great influence on the plants you select for planting. Again, know the requirements of your plants, and keep plants with like requirements together, including watering requirements.

What Types of Plants Should I Choose? Which Ones Perform Best in Rock Gardens?

All right, if the previous question got us down to the nitty-gritty, then this one gets to the heart of what rock garden design is all about. Because let's face it, it is not primarily about the rocks, but about the plants. There is a reason they are called rock gardens: as gardens, plants still take center stage in these features. Nevertheless, well-selected, well-arranged stones will take some of the pressure off of the rock garden plants: they do not need to have the showiness that we expect from standalone plants because their function is to complement the rocks that surround them.

You cannot just slap any old plants in the ground and hope to realize your goal of a knockout landscaping feature. Nor is it easy to decide what is "best" to plant; this will depend, in part, on your design goals. Here are some ideas to get you going, though.

We expect rock garden plants to be low-maintenance, and we forgive them for a certain degree of plainness in the trade-off. The rock garden plants used to complement the rocks should be selected largely with your climate and other practical considerations in mind -- this will help keep them low-maintenance:

  1. Rock gardens in warm climates call for plants different from those used in colder climates.
  2. If you live at high altitudes, you might want to consider a classic alpine rock garden.
  3. If you live in the desert, cacti and other succulents are a sensible choice. As a bonus, they also blend in beautifully with rocks.
  4. If your climate is warm and humid, ferns can be an excellent choice, as are begonias if you desire a flowering plant.

Elsewhere, I present an extensive list of full-sun perennials often used as rock garden plants. In that resource, I discuss gearing your plant selection to growing requirements.

What's an "Alpine" Garden? And How About "Zen" Gardens?

Rock garden design can take many forms. For example, you will hear the terms "alpine gardens" and "Japanese Zen gardens" in connection with such features. What is the difference? How do they tie into this topic?

Japanese Zen rock gardens provide a place for quiet reflection and contemplation. Their approach tends to be minimalist, making as strong a statement as one can with the fewest components. In a typical Japanese Zen rock garden, for instance, a few choice, carefully placed rocks might form a focal point, set off by a large expanse of tiny rocks or sand that serves as a mulch. The mulch can be raked to form an intricate yet simple pattern. Compared to the Western approach, the plant material is de-emphasized.

In the West, the interest in rock gardening began in the U.K. British travelers to the Swiss Alps were fascinated by the alpine plants that they found there and brought some back to try to grow them at home. To this day, rock gardens are sometimes referred to as alpine gardens for this reason. Although we have now expanded upon what a rock garden can be, rock gardening, traditionally (in the West), meant the cultivation of mountain plants and other low-growing plants that can withstand the kind of winter cold to which true "alpine" plants are subjected.

How Should I Arrange the Plants?

We already discussed plant selection, but then there is the issue of distributing the plants amongst the rocks. For an effective rock garden design, you must "have a clue" in this regard before you begin (I told you it would not be as easy as you thought). Rock gardens can not only offer solutions to landscaping problems (such as a yard "plagued" with boulders) but also provide great visual interest in the yard.

Arrange the plants in a rock garden design to look natural. Want a tip to help you achieve this? Turn to nature. Observe a rocky terrain with wild plants growing on it. You probably will not find a hodgepodge of species. What you probably will find are large patches of low-growing plants. If you like creeping phlox, for instance, but never know where to put it, your problem is now solved: a rock garden is potentially a great place to plant creeping phlox. For dry ground, Angelina sedum would be better.

How comfortable will you be in mimicking nature with your rock garden design? It will help to have a clear knowledge of your mind when it comes to design, in general. If you were arranging knickknacks on a shelf, would you tend to wind up with a symmetrical design? If so, rock gardens might not be for you. Evenness in size or distribution looks unnatural in rock garden design. If you want to take a test to determine your garden design philosophy, please consult my article on the history of landscape design. If, after reading this article, you come away thinking, "Wow, those formal garden designers were something!" then rock garden design might not be your cup of tea. If, on the other hand, your reaction is, "Oh brother, that formal garden design sure sounds stuffy!" then you might be ripe for rock garden design.

Do You Have Further Tips on This Subject?

If this set of FAQs did not answer all of your questions, try a more visual approach by viewing my tutorial on How to Build Rock Gardens, where I have included pictures to illustrate the process of building a rock garden from scratch and grouping the plants for optimal effect. These pictures also reveal how important it is to approach a rock-garden project with a landscape color scheme in mind.