You can grow it very fast this time of year. Get a wide plastic container with saltwater (maximum surface area), add a small pump for water circulation, a bit of plant fertilizer and set it in your back yard under direct sun. It will grow extremely fast. Faster then your tang could eat it once it gets growing. Maybe start with about 1ml all purpose liquid miracle grow fertilizer per couple gallons saltwater and adjust from there. Should be able to keep outside until temps drop below 50F at night