Platanthera leucophaea occupies a wide range of soil pH conditions. Tallgrass silt loam and sand prairie soils are usually calcareous, with pH levels of 6-7.5. Soils tend to be more acid in lake borders, fens, sedge meadows, and marshes in the eastern parts of its range, with pH levels ranging from 5.3-6.5. In graminoid fens, this orchid appears to avoid highly calcareous conditions, occupying substrates that have poor to intermediate nutrient levels. Plants found in sphagnum tamarack bogs may root below the sphagnum layer in a more calcareous substrate, or may occur in younger advancing sedge mats. Both high precipitation levels and fire have been suggested to promote flowering of Platanthera leucophaea in tallgrass prairie habitat, but moisture levels appear to be an overriding factor. Over a twelve-year period in Illinois, percent flowering in P. leucophaea populations was higher in wetland habitat and was positively correlated with growing season rainfall. Over time, flowering plants also appeared more quickly in wetland habitat after a severe 1988 drought. Thus, burning would most likely promote flowering in tallgrass prairie wetlands or during years of high growing season rainfall. White fringed orchids require hawkmoth (SPHINGIDAE) pollination for sexual reproduction. The flowers are nocturnally fragrant and place pollinia on the proboscises of hawkmoths as they ingest a high-volume nectar resource from long nectar spurs. As in most orchids, the flowers are morphologically adapted to outcrossing, but plants appear to be self-compatible and probably receive high levels of self-pollination in small populations when pollinators revisit inflorescences. (Bowles 1983, 1985)Specific requirements for Platanthera leucophaea seedling establishment are not well known. Seed germination may be light-inhibited, with dormancy broken by darkness and moist stratification; but successful seedling establishment requires mycorrhizal development with a favorable soil-inhabiting fungus. Seedlings may persist for several years as subterranean protocormbs, receiving nutrients from the fungus. This relationship becomes symbiotic once the plants can produce leaves, and it is likely not species-specific for orchids or fungi.Disturbance may be important in Platanthera leucophaea seedling establishment. Patch disturbance regimes or early-successional vegetation stages are critical for seedling establishment of disturbance-adapted plants, and terrestrial orchids are well known for colonization following disturbance. Platanthera leucophaea populations reach highest densities in disturbed habitats or early- to mid-successional plant communities. Soil fungi responsible for orchid seedling establishment might also respond to similar disturbance or successional patterns. Under apparently favorable conditions or in successional habitats, flowering P. leucophaea have appeared as soon as 5 years after seed dispersal. The root systems of terrestrial orchids are reduced, and evidently require mycorrhizae for proper water uptake and nutrition especially under stress. (Annual tuber regeneration in orchids may also require reinfection by mycorrhizae. Thus the stability of orchid populations is closely related to the ecological conditions of their mycorrhizae, which may be in part regulated by the increased mycorrhizal productivity that occurs after spring burning of prairie. This relationship is dynamic; orchids occasionally enter dormancy (possibly with mycorrhizal nutrition), or decline as mycorrhizae become reduced. Although Platanthera leucophaea is pre-adapted to dormant season disturbances such as prairie fires, growing season damage to vegetative material may weaken plants by limiting food storage.