earth up
To cover the stem or leaves of plants with soil, as to encourage root growth or protect from cold.
earth up: burying plant stems to grow roots or hide them from frost
To earth up is to deliberately pile soil around the base and lower stem of a growing plant, mounding it up to a height typically between 15 and 30 centimetres. The soil is drawn from between crop rows or adjacent land, using hand tools, animal-drawn implements, or tractor-mounted ridging equipment. The practice serves two distinct purposes: stimulating adventitious root formation along the buried stem, or insulating the plant tissue against frost damage and light exposure.
The technique is essential in potato cultivation. As the plant grows, soil is earthed up progressively in two or three passes through the season, burying the expanding stolons and their developing tubers beneath 10 to 15 centimetres of soil. This prevents tuber greening, which occurs when potato tubers are exposed to light and develop solanine, a toxic alkaloid. Potatoes stored in green skin are unmarketable and potentially dangerous. Earthing up also aerates the soil around developing tubers and moderates soil temperature fluctuations.
Celery, leeks, and other blanching crops are earthed up to exclude light from stems and leaf bases, producing the pale, tender tissue that buyers expect. The process begins when plants reach 20 to 25 centimetres in height and continues through the season in several stages. Leeks in particular may be earthed up 40 centimetres or higher by harvest, creating the long white shaft characteristic of commercial produce.
Small-scale growers use hand hoes or specialized earthing-up tools to draw soil manually. Commercial operations employ tractor-mounted ridgers or middle busters, which throw soil from the inter-row space onto both sides of a crop row simultaneously. A two-wheeled ridger mounted behind a single-axle cultivator, or an implement pulled by a standard farm tractor at 4 to 6 kilometres per hour, can earth up a hectare of potatoes in a few hours. Timing is critical: soil must be moist enough to work without compacting, but not waterlogged. Earthing up too early risks burying young plants; too late reduces root development and tuber size.
The term derives from the literal action of turning earth (soil) upward and over the plant. In British English it remains the standard horticultural and agricultural term. North American growers more often say hilling or ridging, though earthing up is understood in commercial contexts. The practice is ancient, predating mechanical implements by centuries, and remains fundamental wherever potatoes, celery, and similar crops are grown on a commercial scale.