Although cultivating mushrooms is complicated and labor-intensive, crop lifecycles are a relatively brief 6 to 7 weeks (depending upon variety) and yields can be very high. Commercial mushrooms are cultivated indoors in two stages: Stage 1 involves preparing the mushrooms’ food (nutrient-rich compost) and Stage 2 is the actual growing and harvesting of the mushrooms themselves.

In Stage 1, natural or synthetic compost is prepared (natural uses straw, hay, and manure) while synthetic can be made of corncobs, cottonseed hulls, corn stalks, dried brewers grains, or cocoa bean hulls without manure. Both kinds require the addition of nitrogen-rich supplements and moisture. Once the odor of ammonia disappears and the compost appears dark-brown, Stage 1 is complete. Heat is then used to pasteurize the material, killing off harmful microbes and insects.

Mushrooms thrive in cool, moist, well-ventilated environments. For Stage 2, compost is usually moved to slabs in a growing room. Shiitake mushrooms grow on logs in the wild, but are cultivated commercially on synthetic logs made from sawdust, straw, corncobs, and other materials. Temperatures must remain cool during cultivation, ranging from 50 to 75°F. Humidity should remain above 70% to prevent drying and splitting. Growers spread mushroom spawn over the compost either using the broadcast method or by planting pieces of spawn about 1.5 inches deep, spaced 10 inches apart.

After 14 to 21 days, soil is spread over the growing beds in a process known as casing. Beds must be watered regularly for about 3 to 4 weeks until the first mushrooms appear.

Harvested mushrooms need high relative humidity to prevent desiccation and loss of glossiness. Humidity between 95 to 98% is ideal. Mushrooms are cooled to between 32 and 39°F, usually via rapid hydrocooling or forced-air and transported in refrigerated trucks immediately after harvest. Properly cooled and packaged mushrooms can be stored for 7 to 9 days at between 32 to 34°F with 95% relative humidity. Even a small rise in storage temperature to 36°F shortens storage life by several days.

Mushrooms are susceptible to strong odors such as onions in mixed loads, so they are generally packed and shipped in bulk cartons with a perforated overwrap to keep humidity in and odors out.

Grades consist of U.S. No. 1 and U.S. No. 2; quality defects include maturity, shape, stem length, diameter, open veils, and trim. Condition defects include firmness, discoloration, spots and decay, and exposed gills. Sizes run from small (three-quarters to 1.25 inches) to jumbo (3 or more inches).

References: PennState Extension, UC Davis Postharvest Technology Center, University of Florida/IFAS Extension, University of Idaho, USDA.



Generally speaking, the percentage of defects shown on a timely government inspection certificate should not exceed the percentage of allowable defects, provided: (1) transportation conditions were normal; (2) the U.S. Depar tment of Agriculture (USDA) or Canadian Food Inspection Agency (CFIA) inspection was timely; and (3) the entire lot was inspected.

U.S. Grade Standards Days Since Shipment % of Defects Allowed Optimum Transit Temp. (°F)
5-1 5

There are no good arrival guidelines for this commodity specific to Canada; U.S. guidelines apply to shipments unless otherwise agreed by contract.

References: DRC, PACA, USDA.


Weekly Movements and Prices, USA
Source: Chart by Gallo Torrez Agricultural Price Trends (GTAPT),, compiled from USDA data.

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