Lava is an interesting medium. While it doesn’t hold much water, the way a planting medium or even rockwool does, lava has strong capillary action, so that it stays moist as long as there is water for it to draw up. The crags and crannies of the uneven surface on an ordinary piece of lava provides spaces that hold moisture and allow the roots to explore.
Lava provides few nutrients, so plants must be fed hydroponic nutrients. If you are growing in containers, you have many choices. You can use either a passive or an active hydroponic unit. The lava should be screened for pea-sized pieces.
Growing in terrestrial lava is more difficult because all watering is drip to drain. A very slow drip unit that supplies hydroponic solution might provide just enough water to keep the plant thriving without much loss to drainage.
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