I grow my grass outside in soil, so during the winter i have no wheatgrass juice.
i did my first planting much earlier this year than usual. i live in the upper midwest and its been a long cold winter. first planting was three weeks ago. its been in the 50's and 60's during hte day, and the 30's and 40's at night. the grass has grown, but very slowly. it seems all growth stops at about 45 degrees, and is very slow at 50 to 6 degrees. doesnt really get going till 60 or 65.
i LOVE my soil grown grass, its so much better than the tray grown stuff. i grow it in plastic rectangle pots, about 18 inches long, 6 inches wides and 8 inches deep.
i use top soil, kelp meal, a trace mineral supplement, some lime (calcium), 'Planters II', and some soil microbes for my growing medium.