20 



consideration and the beds must be kept above 55°. The practice 

 of maintaining a uniform growing temperature is widely favored, 

 although many growers prefer to start their crops at a low tempera- 

 ture and bring on successive growths of mushrooms at slightly 

 higher temperatures. The temperature limits at which the common 

 cultivated varieties of mushrooms can be grown are 45° to 68°. 

 Lower temperatures delay the crop but do not permanently injure 

 the beds. On the other hand, during the time when the mushrooms 

 are on the beds a period of more than a few days with a temperature 

 in the house over 70° will often injure the crop seriously. 



HUMIDITY 



The relative humidity in the average mushroom house during the 

 bearing period ranges from 70 to 80 per cent. This condition is 

 easier to maintain in some houses than in others because of the 

 difference in the exchange of air through cracks and crevices and 

 differences in the proportion of air space to bed space. When the 

 humidity is allowed to drop much below 70 per cent the casing soil 

 has a tendency to dry out too quickly and the surface of the mush- 

 rooms becomes tough and under extreme conditions cracked and 

 seamed. Conversely, if too high a relative humidity is maintained, 

 the mushroom disease known as " spot " will be aggravated by the 

 reduced rate of evaporation of the contaminated water spattered on 

 the mushrooms during the watering of the beds. 



WATERING 



Procedure in watering mushroom beds is governed largely by 

 two objectives : Maintaining in the soil the proper moisture content 

 to induce therein an abundant growth of healthy mushroom strands 

 or rhizomorphs ; and minimizing the number of spots and blemishes 

 on the surface of the mushrooms caused by water spattered on 

 growing mushroom caps. Usually, water is first applied to the 

 beds shortly after they are cased. At this time the beds are watered 

 lightly every day until there is just sufficient moisture in the soil to 

 cause normal strand formation throughout the soil layer. This 

 moderate moisture content is maintained until the mushrooms begin 

 to appear. Care should be taken to avoid an excess of water in the 

 soil at this time, as it may prevent normal strand formation and 

 seriously reduce the subsequent yield of mushrooms. The amount of 

 water necessary to maintain the proper moisture content is quite dif- 

 ferent for different soils and in different localities and seasons. It 

 depends on the relative humidity in the house, the moisture content 

 of the compost, and the water-holding capacity of the soil. In gen- 

 eral, several light waterings are preferable to a few heavy ones be- 

 cause of the danger of excess water percolating through the soil and 

 causing the formation of a wet layer of manure under the soil. Such 

 a layer may prevent the healthy mushroom mycelium lower in the bed 

 from growing up to the soil. Puddles of water on the bed are also 

 objectionable because they tend to stimulate the development in 

 the soil of a harmful green mold and to cause submerged pinhead 

 mushrooms to turn brown and die. On the other hand, if the soil 

 is too dry or if only the upper layer is moist, fewer mushrooms will 



