Start immediately. I'd recommend that you just grow some wheatgrass in any suitable container that you already have. Most anything will do, maybe a large glass bowl or an old baking tin. Here's how.....1. First pour in a liquid fertilizer mix of your own concoction. I use carrot scraps and Clay. The fertilizer is the 'Key'.....2. Pour in a potting mix. I use Lambert's from Home Depot.....3. Scatter the soaked (10 to 12 hours) seeds. Mist with a spray bottle.....4. Cover with a thin layer of potting mix. Mist again with the spray bottle. No other watering is needed.....5. Six or seven days later Cut, Juice, and Enjoy......WY
P.S. Take a picture of your effort and post it here.