calcifugous

Calcifugous, or calcifuge, describes plants that avoid or are unable to thrive in calcareous (lime-rich) soils. The term is used mainly in botany and horticulture to denote species that require acidic soils with low pH and are intolerant of liming or high calcium carbonate levels.

Etymology and scope: The word derives from Latin calx, calcis meaning limestone, and fugere meaning to flee. Calcifugous plants are commonly associated with acidic habitats such as heathlands, acidic forests, bogs, and moorlands. They often form associations with ericoid mycorrhiza, which helps them absorb nutrients under low-pH conditions.

Typical examples and groups: Many ericaceous plants are calcifugous, including rhododendrons and azaleas, heathers (Calluna and Erica), and blueberries (Vaccinium). A range of alpine and woodland understory species also prefer acidic substrates and will perform poorly on lime-rich soils.

Cultivation and management: In gardening and horticulture, managing soil pH is essential for calcifugous species. They require acidic soils, typically kept well below neutral pH, and are harmed by lime or alkaline amendments. To cultivate them successfully, gardeners use acidic composts, pine needles, peat, or sulfur-containing amendments to lower pH, and avoid lime-based fertilizers. Irrigation with neutral or alkaline water can also shift pH unfavorably, so acidifying practices may be necessary. These plants often show chlorosis or poor growth if exposed to liming or repeatedly alkaline conditions.

Notes: Some species are facultative calcifuges, tolerating mildly calcareous conditions but performing best on acidic soils. Calcifuge is contrasted with calcicole, which prefer lime-rich substrates.