1. In British usage, a freezing condition injurious to vegetation, which is considered to have occurred when a minimum thermometer exposed to the sky at a point just above a grass surface records a temperature (grass temperature) of −0. 9°C (30. 4°F) or below. Since 1961 in Britain the statistics refer to the “number of days with grass minimum temperature below 0°C” rather than to ground frost. A fuller discussion is given in McIntosh (1963). See frost. 2. See frozen ground.