Buy Nameko mushroom spawn at a plant nursery or Japanese market. You can also find growing kits online.
Clean a 5-inch-deep plastic tray and dry the tray with a towel. Add 3 inches of potting mix or compost material. Place a thin layer of hay evenly on top of the potting mix. Sprinkle the mushroom spawn on top of this layer. Then add 2 more inches of potting mix or compost directly on top of the hay and spawn.
All types of mushrooms need a growing medium such as potting mix, straw or even a wood log to grow. Some species grow in all of these mediums. Using potting mix is one of the simplest ways to grow mushrooms at home.
Saturate the potting mix evenly with 2 cups of purified water. Mushrooms need a lot of moisture to grow. Place mushrooms on a table or counter and allow time for the spawn to develop.
Place a single layer of plastic wrap tightly over the tray to lock in moisture. Poke two tiny holes in the wrap to allow a small amount of air to circulate inside. It takes one or two weeks for Nameko mushrooms to emerge from spawn.
Remove the plastic wrap completely once you see small mushrooms emerge. Pick the mushrooms when they are 2 inches or taller.