The ability of water to move through narrow spaces against gravity, due to adhesion and cohesion forces. The principle behind wicking beds and how water moves through soil from wet to dry areas.
Capillary action occurs when water molecules are attracted to soil particles more strongly than to each other, creating a pulling force that draws water upward through tiny pores in the soil. In Australian gardens, this is particularly valuable during the hot, dry summers of December to February, when soils can dry rapidly. The height water can rise depends on soil texture—sandy soils in arid zones have limited capillary rise, while clay-based soils common in temperate regions of zones 9-10 can draw water up to 60cm or more. Understanding capillary action helps Australian gardeners optimise irrigation practices and soil structure. Well-structured soils with good organic matter content, achievable by adding compost from your local Bunnings, enhance capillary action and water retention. This is especially important in drought-prone areas like inland New South Wales and Victoria. In contrast, heavily compacted or sandy soils found in tropical zones have poor capillary properties, so improving soil structure through regular mulching and organic matter incorporation is crucial. Gardeners can test capillary action by observing how quickly moisture spreads vertically in their soil after watering.