Home » Craft » Lava Rock Bonsai

Lava Rock Bonsai

Lava rock bonsai are a lively take on a traditional root-over-rock bonsai.

This project is all about creating a fun yet serene tray garden. An airy Euphorbia californica is mounted on a porous dark lava rock displayed off center on a crisp rectangular white marble tray. The light, flutter-leafed euphorbia is set off by dark, textured lava rock and grounded by the marble tray. A surprising magenta twine holds the bonsai to the lava rock. Plants with shallow root systems work well for this project. If you cannot find a Euphorbia californica, or would like to use a different plant, look for a jade plant, schefflera, or ficus.

If you’re working with a lava rock that doesn’t have a natural depression or groove one can be chiseled or drilled very easily. Lava rock has a very porous surface that is easily chipped away.

Water your plant and rinse the lava rocks, both small and large, the day before you start the project. The rocks should be clean and not soaking wet when you work with them. The idea behind watering the plant the day before you begin the project is to allow the plant time to absorb the water and not be stressed, which will help it adapt to its new home with fewer problems.



  • Tray or saucer (I used a 15-inch rectangular tray made of marble) (A)
  • 1 cup of small decorative black lava rock (B)
  • Black lava rock, preferably with an existing hole or depression and a flat bottom so that it sits level with a tabletop (find lava rocks at pet stores or landscape supply stores) (C)
  • Euphorbia californica (or other plant suitable for mounting) (D)
  • Hemp twine (any color; I used magenta) (E)



  • Star drill or chisel
  • Hammer
  • Scissors

Fill the tray with the small decorative lava rock.


Find a natural depression or hole on the large lava rock for the Euphorbia californica to sit on. If your rock does not have a natural depression or hole, create one with a drill or chisel.


Loosen the Euphorbia californica by squeezing the sides of the pot, and gently remove the tree from the pot.


Gently remove any excess soil with your fingers, leaving a little bit of soil on the roots.


Plant the tree in the hole, placing most of the roots in the depression with the soil. Add more soil if needed. You can leave some of the roots exposed on the rock surface.


With the hemp twine, tie the exposed roots in place, wrapping the twine around the rock front to back, back to front, and side to side. Once the tree feels secure, tie a knot in the twine and cut off the loose ends. You can remove the twine once the tree has had time to grow and the roots are attached to the rock. If you opt to keep the twine, it may disintegrate over time and need to be replaced periodically. Place the plant to one side of the tray, with the curve of the tree extending out over the tray.



Water by submerging the tree in water or by pouring water over its roots. If you’re watering by submerging the tree, place the entire rock under water for 10 minutes. You’ll see a steady stream of bubbles as the water fills the air space in the lava rock and pushes out the air. You may need to water as often as every three days, but it should be at least once a week. When the rock mostly stops dripping, place it back on the tray with small lava rock. Cut back on the watering in winter.



Euphorbia californica likes a lot of light—very bright indirect light works well. A south-facing window would be a good choice.


There is very little soil in this planting, so I recommend using a diluted liquid fertilizer every week during the growing season.