14 CIRCULAR 609, U. S. DEPARTMENT OF AGRICULTURE 
assures a good growth of fire fang due principally to Actinomyces spp., 
which tend to discourage the growth of weed molds and will usually 
bring the air temperature up to 130°, which is sufficient to eradicate 
insect pests. 
7. Moisture is controlled by watering the beds during the com- 
posting. More water is lost during the first 4 days than during the 
remainder of the sweating out, and it is necessary to keep the center 
of the beds quite moist during this period. In the experiments at 
Arlington Farm the beds were broken up and remoistened after 7 or 8 
days to get an even distribution of water in the manure. This should 
not be necessary in commercial practice because the manure will be 
either partly composted en route to the grower or put through a short 
fermentation on the wharf while it is being moistened and broken up. 
8. The appearance of the manure pH value and lack of an am- 
monia odor should be used to determine when the composting is 
complete. This will probably be between 10 and 12 days, depending 
on the condition of the manure when placed in the beds. 
9. Growers will be surer to eradicate insects if sufficient auxiliary 
heat in the form of steam is liberated into the air of the house during 
the last 2 days of composting to raise the air temperature to 130° F. 
At this time the difference between the air temperature and manure 
temperature will have receded to about 5°, so that there will be little 
danger of driving the manure temperature above 140°. No fumiga- 
tion will be necessary if the air temperature in all parts of the house 
and the floor temperatures reach 130° for several hours. Otherwise, 
the usual cyanide fumigation at peak heat is recommended. 
10. After composting the usual procedure is followed for spawning, 
casing, disease and insect control, and other cultural practices. 
SUMMARY AND CONCLUSIONS 
Studies are described leading up-to a method of fermenting organic 
composts indoors under controlled conditions that makes the prepara- 
tion of mushroom compost more nearly a controlled industrial process. 
In shallow layers of compost, such as standard mushroom beds, fer- 
mentation conditions of temperature, moisture, and aeration were 
controlled close enough to the optimum to produce a satisfactory 
mushroom compost in less than 2 weeks. 
For experimental comparisons of the effect on the production of 
mushrooms of different substitutes and supplements for stable manure 
the indoor composting method has the inherent advantage of per- 
mitting the experimenter to conduct preliminary tests cheaply in small 
glass containers and later, in making yield tests, to replicate compost- 
ing conditions in trays or test plots without the cumbersome and 
expensive replication of outdoor compost heaps. 
There are several principles learned from the studies on indoor 
composting that are of interest to commercial growers: 
The sweating out process following the usual outdoor composting 
should be considered as an integral and important part of the com- 
posting process and not merely as a means of eradicating harmful 
fungi and insects. 
Outdoor composting may be considerably shortened or eliminated 
altogether, provided sweating out is prolonged approximately 1 day 
for every 3 days omitted from the outdoor composting. 
