The fine art of bonsai arrived in Hawaii when the first Japanese immigrants came to work sugar plantations in the late 1800s. Bonsai masters in Hawaii continued to shape dwarf trees in the traditional manner until the 1940s, when many Japanese Hawaiians destroyed or abandoned their bonsais to avoid being persecuted as pro-Japanese sympathizers. After WWII, new enthusiasm for bonsai emerged in Hawaii, and we have the adventurous spirit of this new generation of artists to thank for lava rock plants. Dwarfed tropical plants rooted into chunks of Hawaiian lava rock represent the fusion of cultures, and are surprisingly easy to care for.
Select a decorative waterproof container, which is 1 to 2 inches deeper than the height of the lava rock on which your plant is growing.
Fill the bottom of the container with 2 to 3 inches of smooth, clean pea sized pebbles.
Place your lava rock plant on top of the pebbles. Adjust the plant's height by adding or removing more pebbles as necessary so that the lava rock rests on top of the pebbles and the bottom half of the rock is below the rim of the container.
Fill the container with filtered water or rainwater just up to the top of the pebbles. Avoid using chlorinated or hard water to prevent harmful salt buildup on the lava rock. The porous lava rock will soak up the water from the bottom like a wick and provide moisture for your plant. Keep the water level constant by checking the container daily and adding more as needed.
Fill a 1-gallon bucket with enough filtered water to cover half the lava rock. Remove the lava rock plant from the decorative container and gently place it in the bucket for about 10 to 15 minutes, until the entire rock is wet. Do this once a month or as often as once a week if you live in a dry climate. Some lava rocks are more porous than others, so you will need to watch your plant carefully at first to make sure it is receiving enough water. If you see drooping leaves, you will need to submerge the rock in water more often.
Mist your lava rock plant daily in the morning hours with a spray bottle filled with filtered water. Do this when the plant it is not receiving any direct sunlight.
Feed your terrestrial plant by adding the recommended amount of liquid plant food to the water as you soak the plant in the bucket. Do this once a month while your plant is actively growing in summer and spring. Omit the fertilizer in the fall and winter months. If your lava rock plant is a bromeliad, only foliar feed the plant once a month with half strength liquid plant food in a spray bottle but, unlike terrestrial plants, do not add the plant food to the soaking bucket water.