This is a question that often comes up when talking about Zen rock gardens and other types of Japanese gardens. I have talked with Japanese garden designers both in Japan and North America and the answer is not as easy as it may seem because there are actually a variety of different styles of gardens.
So, what kinds of rocks are used in Japanese gardens? A variety of rocks are used in Japanese gardens depending on the style of garden we are talking about. A different stone is used for Japanese dry rock gardens (sometimes called Zen gardens), steeping stones, garden paths, waterfalls etc.
In the rest of the article I will go into more detail as to what type of rock is used in each style of garden and how they are best used.
Japanese Dry Rock Gardens (Karesansui)
One of the most popular types of rock gardens is the Karesansui, or dry rock garden. These gardens are often raked to show patterns in the stones. These patterns represent waves for ripples in the water and they guide your eyes in a particular direction or to a focal point. People often mistakenly call this sand, but it is actually a few different sizes of gravel. Something is fine sand does not hold up to the wind and is unable to hold its structure.
Outside of Japan did you primarily have two options. The first of being a pea gravel, which can work and comes in a variety of colors but can sometimes seem artificial. Many Japanese gardens outside of Japan use two different sizes of turkey grit. You are more likely to find a Turkey grit at a farm feed store rather than a garden store. The turkey grit will most likely be the closest to traditional Japanese garden gravel that you will find. Unfortunately you are restricted to a gray two bright white color.
These types of gardens are often found at the Buddhist temples in the front or rear gardens. They are meant to be the garden to be meditated upon from a viewing room. Thus they are often meant to be viewed from a particular angle as opposed to strolling garden. The boulders often represent famous Chinese mountains or sometimes create the effect of a dry waterfall, with the gravel representing the ocean.
Boulders In A Japanese Garden
Boulders are one of the most important aspects in a rock. Ideally, the boulders and stones that you choose will be darker in color and I have less of a bright yellow beach look. You should avoid Sharp edges on the boulders and choose Stones with more natural and soft edges.
A major issue with boulders is how they are placed. You often want the widest part of the stone at ground level. Which means that sometimes half or more than half of the stone will be buried. We have a tendency to want to be bold and make a statement but the rocks should protrude from the ground in a natural way.
Ignore Soil lines
This side of the rock that is exposed to the air Will become more weather and will have a color variation compared to the part of the stone that is buried. You should however overlook this color line in focus more on the overall shape of the rock and concentrate on which edges you want highlight. Once you place the rock in the garden it will then also begin to take on new weather patterns. This may take 10 years or so but in the long run you will have a much better looking garden if you focus on the shape and how the rock fits into the overall scene.
Stepping stones (Tobi-ishi)
I currently live in the northeastern United States and I have found that Pennsylvania Fieldstone is a great stone to use for stepping-stones. Garden path stones can be a variety sizes that usually take a round or square shape. A stepping-stone should never be smaller than your actual foot size, and a good rule of thumb is to make sure that they are one and a half to 2 feet in diameter. You also need to think about how you place them and how naturally you can walk on them one foot after another. This often will create a weaving path that is slightly offset. Some places where the path may turn or where you want someone to stop and observe something you can use a much larger stone where 2 feet would then be placed to stand on.
The thickness of the stepping-stone is something also that needs to be highlighted. I mentioned Pennsylvania Fieldstone because it is often easily three to four inches thick. The stones should be roughly the same height above the ground, making it easier to walk. They should also be buried half way in the ground to stabilize them and make sure they don't move when you step on them.
For these reasons flagstone is usually not a good choice of garden path stone. Flagstone tends to have sharper edges and is often too thin to have the presence a Japanese garden stone needs. They tend to sink in and get lost by the surrounding material.
Nobedan pavement or pathways do not only get someone from point A to point B but unite different areas of the garden, often in a roji tea garden. They are often done in straight rectangular patterns with the flat stone arrangements uniquely and tightly fit together. Nobedan paths may look like flagstone but they are constructed with cobbles and thicker granite slabs and sometimes long, narrow rectangular pieces.
Nobedan pavement can also be seen at large entranceways, near gates, and also evolve into larger full patios. They can can be very symmetric, tightly shaped together, or take on an artistic blend of straight lines with circular and irregular shaped stones as well.
Setting Stones (Ishigumi)
The art of setting or placing stones is an art unto itself. The importance dates all the way back to the first Japanese gardening book called Sakuteiki, in which they clearly lay out the spiritual power that a stone can have. In Japan’s native religion of Shinto, both plants and rocks have a natural power to them. Inanimate objects also have a power and should be respected just like living things, hence there is a deep power that a stone rock garden can have. The Sakuteiki mentions that you should “follow the requesting mood of the stone,” showing the respect that should be paid and the life-force that flows through the stone is to be acknowledged.
Modern Dry Rock Gardens
Modern Japanese garden designers have studied tradition and are now also expanding on that tradition to bring in more elements of self-expression.
This garden in Nara has added a practical element to it by using pea gravel in between the "islands." This miniature scene is a nice addition to a front entrance and it also relieves the owner of having to be so meticulous with the raking of the gravel to create waves. Although there are also stepping stones in the back it looks like walking on the brown colored gravel is also acceptable. It is good to see gardeners adapting the garden to modern times and allowing function to play a part of the garden, rather than loosing the tradition all together.
The modern stepping stone design to the right also shows how the "S" curve then blends in and out of a sort of checkerboard design of square stones. The circular stones were most likely hand chiseled to get that uniform round edge as well.
As you can see, a large amount of different kinds rocks are used in a Japanese garden. Each has a different use and is aiming to achieve a different affect. Stones really are the backbone of the traditional and modern Japanese garden. If you would like to learn more about modern rustic gardens or how you can design a garden that fits your style, visit us at ShizenStyle.