Cultivation of Morel Mushrooms


By Gary Mills Morel mushrooms are one of the most desirable of edible mushrooms.  The morel fruitbody is diagnosed by its sponge-like appearance, displaying a characteristic ribbed and pitted cap; the cap being attached to and continuous with the stipe, with both the cap and stipe being hollow.  Morels can be collected in the wild during the spring of the year in diverse geographical locations that include grasslands, mixed conifer and hardwood forests, northern rain forests in the Pacific Northwest, and mountainous regions of semi-tropical islands, for example, Jamaica.  Morels can also be found growing in disturbed areas such as flower beds and in recently burned woods and in association with living apple, ash and liriodendron trees while massive fruitings have been described around dead elm trees.

Morels have been grown indoors in controlled environments since Ower published his results in 1982 and the complete life-cycle has been described by Volk and Leonard in 1990.  Both research groups involved in these studies recognized the importance of sclerotia as an integral part of the life cycle of the genus Morchella, with the cultivation of sclerotia being a key discovery for being able to grow morels commercially.

Sclerotia cultivation consists of inoculating a sterilized cooled container with the vegetative mycelium, either petri plate mycelium or mycelium covered pieces of grain characterized in the mushroom industry as grain spawn.  The container may be rigid such as a glass or polypropylene jar, or autoclavable polypropylene bags commonly used in the mushroom industry.  The contents of the sclerotial container consists of a bottom layer of hydrated grain, wheat for example and a top layer of hydrated soil.  The key to cultivation of morels is the large scale production of sclerotia.

Following inoculation of the sclerotia containers the cultures are sealed and incubated 4 - 5 weeks.  During this time mycelium grows through the soil layer at an average rate of 1.5 cm/day.  Upon reaching the nutrient grain layer hyphal elongation slows and extensive secondary hyphal branching begins.  At this point the hyphae hydrolyze the grain, assimilate the released nutrients, translocate these nutrients back to the older hyphal cells in the soil layer. Three weeks after inoculation sclerotia change from white to a rust color and as maturation continues the sclerotia become brown due to melanization.  Once the sclerotia are mature and completely melanized, they can be harvested for planting.

The soil layer and mature sclerotia are removed from the container and planted in standard horticulture trays.  Morel tray cultures are prepared by adding a soil-sclerotia mix to the trays and the contents of the tray are covered with a moist layer of soil.  Once prepared the cultures are lightly misted and allowed to colonize in the dark for a period of 6 days.

Cultures are induced seven days after culture preparation.  Induction entails the thorough hydration of sclerotia, which stimulates the adventitious hyphae growing from the sclerotia to commence the fruiting process.   The following developmental sequence is observed during ascocarp growth.

3 DPI (days post-induction) extensive hyphal growth covers the cultures accompanied by conidia formation.  Seven-to-ten days post-induction primordia, 1 mm in height and diameter, arise from a single hyphae.  Primordia elongate at a rate of about 1 mm/day giving rise to an apothecial fundament that is white in color.  By 18 - 21 days postinduction the fully differentiated fruiting structure is 1 cm in height and looks like a small white morel with a distinct cap with ridges and a stipe.  From this point onward the growth rate accelerates to 1 - 1.5 cm/day and there is a color change from white to gray.  Ascosporogenesis coincides with a decrease in growth rate, another change of color to tan, with the final ascocarp color becoming pale ochre at ascospore maturity.  Morels are harvested before ascosporogenesis.