an American gardener in such an area may only have to plan for several nights of cold temperatures per year, while their British counterpart may have to plan for several months. In addition, the zones do not incorporate any information about duration of cold temperatures, summer temperatures, or sun intensity insolation; thus sites which may have the same mean winter minima on the few coldest nights and be in the same garden zone, but have markedly different climates. For example, zone 8 covers coastal, high latitude, cool summer locations like Seattle and London, as well as lower latitude, subtropical hot summer climates like Charleston and Madrid. Farmers, gardeners, and landscapers in the former two must plan for entirely different growing conditions from those in the latter, in terms of length of hot weather and sun intensity. Coastal Ireland and central Florida are both Zone 10, but have radically different climates 99% of the year . The hardiness scales do not take into account the reliability of snow cover in the colder zones. Snow acts as an insulator against extreme cold, protecting the root system of hibernating plants. If the snow cover is reliable, the actual temperature to which the roots are exposed will not be as low as the hardiness zone number would indicate. As an example, Quebec City in Canada is located in zone 4, but can rely on a significant snow cover every year, making it possible to cultivate plants normally rated for zones 5 or 6. But, in Montreal, located to the southwest in zone 5, it is sometimes difficult to cultivate plants adapted to the zone because of the unreliable snow cover. Many plants may survive in a locality but will not flower if the day length is insufficient or if they require vernalization (a particular duration of low temperature). There are many other climate parameters that a farmer, gardener, or landscaper may need to take into account as well, such as humidity, precipitation, storms, rainy-dry cycles or monsoons, and site considerations such as soil type, soil drainage and water retention, water table, tilt towards or away from the sun, natural or manmade protection from excessive sun, snow, frost, and wind, etc. The annual extreme minimum temperature is a useful indicator, but ultimately only one factor among many for plant growth and survival. Alternatives An alternative means of describing plant hardiness is to use "indicator plants".