Pre-departure trip to Kennett Square, Pennsylvania

I visited Kennett Square (Chester County, PA) this past month to tour some large-scale mushroom production facilities and learn a bit about the state of the field and market.

The production of white button, cremini, and portobello mushrooms begins with composting. These three varieties of of the same species of mushroom (Agaricus bisporus) compose the vast majority of the market.  A. bisporus is a secondary decomposer, so it grows on substrate whose nitrogen content has been chemically changed by microorganism-mediated decomposition into a form that A. bisporus can use. (Laurel Valley Farms, PA)

Phillips is one of the largest producers of commercial mushrooms, both button-type and specialty species. Consistent with patterns throughout agriculture in the US, mushroom farms have been consolidating and stratifying production between very large-scale integrated operations and tiny niche organic/local producers. 

A producing bed of A. bisporus. This operation is an example of a highly modernized system that departs from the traditional "Pennsylvania double" growing houses. All conditions (temperature, humidity, etc) are closely controlled, and spacing maximizes growing and harvesting efficiency.

Mushrooms form in the compost that has been fully colonized with Agaricus bisporus mycelium. Portobello, cremini, and white button mushrooms are all varieties of the same species of mushroom. Cremini are brown, buttons are white, and portobello are mature cremini.

This bed of A. bisporus is in a traditional "Pennsylvania double" growing house has been recently harvested, but new flushes quickly develop until the nutrients in the substrate are depleted . When cremini are harvested, workers leave a few to further develop into portobello. The Kennett Square area of Pennsylvania has a long history of mushroom cultivation. See this NPR article for a brief history of how the area became the "mushroom capital of the world" and the current state of production.

Phillips is also a major producer of specialty types including shiitake (Lentinula edodes, pictured), oyster mushrooms (Pleurotus ostreatus, Pleurotus citrinopileatus, etc) maitake (Grifola frondosa), "pompom" (Hericium erinaceus), though the market for these species is limited.  Jim, the GM of Phillips,  makes a joke that seemed to be common amongst mushroom growers, something along the lines of "it takes a lot of money to make a little money in the mushroom business," referencing the need for space, climate control, sourcing of appropriate substrate, strain development, and marketing among other things to make production commercially viable. Here's a video of Jim giving a quick tour of the facilities.

Golden oyster mushrooms (Pleurotus citrinopileatus) grow in bags of pasteurized straw. Oyster mushrooms are often small-scale mushroom grower's first crops, as oyster mycelium is tenaciously fast-growing and Pleurotus species are primary decomposers, so there is no need to compost the straw before inoculation. Some other species, like maitake (Grifola frondosa), can be very challenging to grow and require high-level sterilization and climate control.

Hericium erinaceus (known as pom-pom, lion's mane) is a peculiar-looking fungus. The high humidity in the growing facilities is clearly visible in this image. Many of these specialty varieties are grown in these plastic bags with a gas-exchange patch, and when the substrate (sawdust, grain, etc) is fully colonized, small holes are punched in the plastic to allow the fruiting bodies of the fungal mycelial mass to emerge.

The internal structure of H. erinaceus. 

Mushrooms are visible growing at the base of a hemlock tree in Longwood Gardens in Chester County, PA.

More pictures are on my flickr photostream (linked in the right sidebar)