Volcanic soil is by far among the most fertile. The abundance of sodium, calcium, magnesium and especially potassium make volcanic zones ideal places for growing vegetables and fruit trees, without having to resort to irrigation systems.
However, this is true once the products of volcanic eruptions, lava and pyroclastic products, have become cultivable soil. Indeed it is difficult for the roots of any shrub to penetrate the crust of a lava flow. Ashes are also inhospitable, so much so that in some parts of the world, like Iceland, vast deserts form. This is because they are nevertheless very sharp volcanic glass particles.
It usually takes 100 years for the lava and pyroclasts to turn into soil and be ready for cultivation.
