How to Make a Mushroom Grow Box

Sterilize all your tools and materials using alcohol wipes. This includes the plastic sheeting, your hands and any tools you use to handle or spread the compost and spores. Keeping the environment as sterile as possible will help to keep pests and other fungi at bay.

Choose a box that's deep enough to fit at least 6 inches of compost and a 3-to-4-inch layer of straw. The more nutrients your mushrooms can reach, the better. You can build your box from wood or use a cardboard box, a disposable Styrofoam cooler, or a plastic bin. Clay will suck water out of the compost and can lead to some humidity problems, and wood can do the same, but as long as you line your box with plastic, you'll be fine.

Set up your box and line it with the sterilized plastic sheeting. Keep the plastic tight to the inside of the box and let it overhang the edges to keep moisture in. Leave the top of the box open to help with ventilation.

Store your growing box in an area where you can control the amount of moisture it gets. If you want an outdoor box, make sure to situate the box in a sheltered spot, where it will get only indirect sunlight. Too much sunlight and heat will kill your spawn.

Fill the growing box about three-fourths of the way with compost. Use a cooking thermometer to measure the temperature of the compost. Do not add your spawn until the temperature is below 86 degrees F (30C). Higher temperatures will kill your spawn.

Separate the grains of spawn from one another, getting them as fine as you can. Then spread them evenly throughout your compost.

Monitor the compost to check for mycelium growth. The first downy growth should appear in three to four days, and the mycelia should permeate the compost after about two weeks. It's then time to add your casing.

Lay in a 3-to-4-inch layer of wet straw in order to trigger the mushrooms to grow from the mycelia. Depending on the mushroom strain, your first crop should begin to grow in six weeks to two months.