CANNA 9221801 Substra Vega part A 1-liter is part of a complete 2-part nutrient for plants during the growing stage. In substrate cultivation, the soil is replaced by an inert medium. Inert mediums, such as rockwool and sphagnum peat, do not contain any nutrients. Substra provides the best nutrition for growing in inert substrates. CANNA Substra works best with run-to-waste or simple hand watering. Substra Vega part A is easy to use. Just add part A first in the water then add an equal amount of part B, mix well, and water your plants.