What temperature and humidity does button mushroom need to fruit?

Button mushroom has two clear temperature needs. During spawn run the compost should be kept warmer, generally around 22 to 25 degrees C for the white mycelium to spread through the compost in about two weeks. After you apply the casing soil, you must drop the room to roughly 14 to 18 degrees C to trigger pinning and fruiting, and that lower temperature is exactly why button mushroom is mainly a winter or cooled room crop in India. Keep humidity high, broadly around 80 to 90 percent, with good fresh air exchange so carbon dioxide does not build up, otherwise you get long stalks and small caps. If your room stays too warm after casing, you will see thin mycelium and very few pins, which matches what you describe. Use a cheap thermometer and a hygrometer, and adjust with ventilation, light misting and timing the crop for cooler weeks. For precise targets for your strain, check with DMR Solan or your KVK.