Line the strawberry baskets with plastic wrap or plastic bags to waterproof them and enclose the soil. Mushrooms need moist foundations and the water will destroy paper baskets over time. Fill the baskets to within 1 inch of the brims with rich, moist organic compost.
Inject white, button or oyster mushroom cultures into the compost. These cultures are available at garden shops and nurseries and come in both injectible and plug forms. The culture contains mushroom-growing material.
Put the baskets in a dark, enclosed drawer or cupboard for growing. Set a heating pad to 70 F and put it near the baskets to keep the space warm. Leave the mushroom cultures for three weeks of rooting.
Check the compost for white filaments, which indicate mushroom culture rooting. Fill the baskets to the top with more compost and spray the surface lightly with water. Put a cloth over each basket, then put them back into the dark growing space. Turn the heating pad down to 55 to 60 F for mushroom formation.
Spray the cloths and compost with water every day for moisture and humidity. Look for mushroom sprouting in three to four weeks.