A low-lying area where cold air collects on still nights, making it significantly colder than surrounding higher ground. Frost pockets experience more severe and more frequent frosts — avoid planting frost-sensitive plants there.
Frost pockets form due to the physical movement of cold air, which is denser than warm air and naturally flows downhill like water. In Australian gardens, especially in temperate zones (zones 6-8), these areas commonly occur at the base of slopes, in valleys, against south-facing fences, or in sheltered courtyards where air cannot circulate freely. Cold air becomes trapped, sometimes 3-5 degrees colder than nearby open areas.
Identifying frost pockets is crucial before planting frost-tender species like citrus, avocados, or tender perennials. Mark these areas during your first winter by observing where frost lingers longest, particularly on clear, still mornings in June-July. You can also watch for plants that consistently suffer frost damage year after year.
To protect plants in frost pockets, consider strategic placement of cold-hardy species instead. Alternatively, improve air drainage by removing barriers or planting on raised mounds. Installing frost cloth or temporary wind breaks from April onwards provides protection for vulnerable plants. Mulching heavily around the base helps moderate soil temperature fluctuations.
Available from Bunnings are frost protection products including frost cloth and temporary stake systems. For zone 5 gardens, avoiding frost pockets altogether is often the most practical solution when selecting permanent plantings.