Pleurotus ostreatus: hybrid cottonwood production

dwheeler at dwheeler at
Sun Mar 23 16:51:06 EST 1997

At a Clackamas County, Oregon tree farm stumps of hybrid cottonwood were
created in 1995 by cutting the tree about 3 feet from the ground. Within a
week, several (5-8) stumps were inoculated by members of the Oregon
Mycological Society Cultivation Group with Pleurotus ostreatus, or Oyster
mushrooms. On March 15, 1997 a flush was observed on two of these logs.
Since the methods of stump inoculation varied, these results may be of
interest to others interested in cultivating mushrooms outdoors.

The diameter of these trees was between 2.5 and 8 inches at 3 feet from
the ground. One log was inoculated with sawdust/millet spawn by cutting
kerfs, as per Paul Stametes Growing Gourmet and Medicinal Mushrooms. This
log has yet to produce anything, and the kerfs have now nearly fallen off
the stump. Probable reason for lack of fruiting was that inoculation took
place too close to initial cutting, and the stump was not gidled at the

Another log was inoculated with wooden dowels, arraned on the cut surface
of the log, spaced out near the cambium layer of the stump. This stump
produced has produced no mushrooms at this time. Presumed reason is that
the stump was not girdled at the time of cutting. Several suckers or
sprouts were observed to erupt from both the side of the stump below the
inoculation point, and near the base of the stump. These suckers did not
produce viable shoots, and the tree eventually died. But presumably it was
still capable of fighting off the P. ostreatus inoculation.

Two large logs, 6-8 inches in diameter, were inoculated in multiple
methods: by dowel, spaced up and down the stump; by top cap, where a 1-1/2
section of the top stump is cut off, spawn is poured over the top, then
the top section replaced and nailed with a zinc-anodized nail; or placing
fresh spawn on the top of the stump and using a plastic bag to hold the
spawn on the stump. The key to the fruiting of these two logs seems to
have been a preparation variance: one stump was girdled at the base with a
chain saw, the other was not. The girdled tree was the first to fruit
(1996), and also the most prolific producer of mushrooms. The non-girdled
log failed to produce P. ostreatus, send out several basal suckers, and
has not produced any kind of mushrooms except a Stereum sps. to date.

Two other logs had important results: One did not produce P. ostreatus,
but did produce a prolific flush of Stereum or Trametes-like fungi, with a
greenish tint on the top and interesting, purplish-tubes on the bottom.

The last log was inoculated with a single cap inoculation, with basal
girdling and co-inoculation at the girdling wound. This produced the most
fungi in 1997, with a majority of the fungi forming not from the stump,
but rather from the roots.

This multiple inoculation method suggests that girdling hybrid poplar
(cottonwood) trees is important for Pleurotus ostreatus growth. Stumps
should be created in January or February and allowed to stand. Girdling
the newly created stumps seems important to mushroom production. By March
22, 1997, no fresh mushrooms were seen. Mushrooms not picked had
dessicated on the stump.

Daniel B. Wheeler

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