The bottom boards should be cleaned after the [[cleansing flight]], which is quite early in the year. This is done by removing the bottom board and scraping all of the downfall off the board with a metal scraper. Keep in mind that the downfall might contain infectious material, so discard it properly, for example by burning it. This way you can minimize the risk of spreading [[infectious disease and parasites]]. The bottom board then is either flamed with a gas torch or washed with a sterilizing medium, such as Virkon solution (Finland).
During winter the flight entrance is usually kept open, in order to ensure proper ventilation. During the spring, the flight entrances should be downsized and this is usually done during the same visit to the bee yard as the bottom board cleaning.
*In southern Norway in contrast, the bottom board cleaning is done from mid-April to mid-May, while food consumption is also checked at the same time.