An Introductory Guide to Iwagumi

For someone who wants to try an Iwagumi layout for the first time

Each rock used in Iwagumi has its own name. There are special rules of Iwagumi, such as the way its substrate is laid and the order of rock placement. This section discusses the basics of Iwagumi that every beginner should know.

The names and functions of rocks

Oyaishi
This is the primary rock in Iwagumi. It is the largest rock as well. Select the best one in terms of shape and character. Its height should be approximately 2/3 of the height of an aquarium.

Fukuishi
This is the second largest rock and is placed on either left or right side of the Oyaishi. Select a rock with the same or similar texture as Oyaishi to give uniformity to the overall Iwagumi.

Soeishi
It is smaller than Fukuseki and is placed next to the Oyaishi, along with the Fukuseki. It plays a key role in the flow that the Oyaishi creates by bolstering the presence of the Oyaishi or accentuating the strength of Oyaishi.

Suteishi (a sacrificial stone)
It is a small rock that does not stand out in the overall arrangement of Iwagumi, and it may even become hidden by aquatic plants occasionally. Its presence has a subtle, simple elegance.

What is Sanzon Iwagumi?

It is the most basic composition of Iwagumi in which the largest rock is placed in the center and a smaller Fukuseki and Soeishi are placed to the left and right of the Oyaishi. This type of composition is called Sanzon Iwagumi due to the resemblance of the rock arrangement to Buddhist triads.

Should the number of rocks be seven, five, or three?

It is considered good to have an odd number for the rocks that play the major parts in scenery. An even number of rocks tends to look symmetrical or makes scenery appear split. Iwagumi looks more attractive if the center of the balance is somewhat shifted to one side or the other.

A: An even number of rocks tend to split evenly.
B: Having an odd number of rocks prevents the even split.

Why is the Oyaishi tilted?

While Sanzon Iwagumi in Japanese gardens, such as those in the dry garden style, often appears upright, the Oyaishi in Nature Aquarium is placed in an angle to express the flow of water by appearing to bear the force of the water.

Iwagumi Layout Procedure

Lay a thin, even layer of the substrate.
Although the thickness of the substrate for a layout with driftwood is kept low in the front of an aquarium and increases gradually toward the back, the substrate for an Iwagumi layout is laid thin and evenly initially. This is different from the way the substrate is laid in other layouts.


Arrange Oyaishi according to the golden ratio.
It is the cardinal rule to start an arrangement by placing the Oyaishi first. An attractive and well-balanced Iwagumi can be created by placing the Oyaishi following the golden ratio of 1:1.618 (roughly 2:3).


Arrange the remaining rocks from the largest to the smallest in descending order of size.
Following the placement of Oyaishi, remaining rocks are placed in descending order of size: Fukuseki first, then Soeishi, and Suteishi last. The positions of rocks are decided by watching the balance of the angles and orientations of the rocks.


Finish the substrate by mounding soil.
Mound soil by spreading additional Aqua Soil over the existing substrate using a small plastic container. Let some Aqua Soil flow in between rocks to produce a sense of continuity. Finish the substrate by spreading powder type Aqua Soil over the mounded soil.

A key point for planting

Since aquatic plants can soften the strength of rocks, aquatic plants are used to create a balance in the strength among the rocks. Low-growing plants are used to accentuate the details of a rock arrangement. Planting aquatic plants next to or in-between rocks is key for enhancing the natural feel of the layout.

                                                                                                       
                                                                                                        Source:  aquajournal.net