|Crow Dog Native Ferns and Gardens|
In nature, native ferns are strong indicators of soil pH. For example, Cinnamon Fern (Osmunda cinnamomea) is found at its full potential in strongly acid soil (pH ~4.8-5.7) with full sun and constant moderate to high soil moisture. With the same light and moisture regime, but with higher pH, Cinnamom Fern is absent, or if rarely present, it is noticeably stunted. Conversely, the Northern Maidenhair Fern (Adiantum pedatum) is found in slightly acidic to circumneutral (pH ~5.8-7.0) soil in dappled shade and average soil moisture. It too can be rarely found stunted in highly acidic soil. Some native ferns, such as Christmas Fern (Polystichum acrostichoides), flourish in virtually all pH regimes except in extremes of acidity or alkalinity.
Soil pH is controlled by several ecological factors. In nature the overwhelming factors are bedrock mineral chemistry and the presence or absence of soil organic matter and micro-organisms that feed on the organic matter. Generally when bedrock weathers initially from the influence of water and air, some strongly reactive minerals, such as feldspar and other minerals, are changed into clays. Some minerals, like quartz, do not change chemically, but are released as grains of various size embedded in the clays. Also in early rock weathering, a few of the metals (often Iron and Aluminum) are oxidized and become moble in the soil through ground water. Other metals are strongly bound to clays and are not mobile through soil solutions.
The original mineral content of rocks strongly affects the pH of fully developed soils. For example, rocks such as granite, metamorphosed granite (granite gneiss), some shales and slates, and some volcanic rocks have high Aluminum content. Soil derived from these rocks will also be high in Aluminum content and strongly acidic, because Aluminum readily exchanges with Hydrogen at binding sites in the soil. This produces mobile Hydrogen that binds with sulfate, nitrate, and carbonate in the soil to form acids. These rocks are typically low in alkaline metals such as Calcium, magnesium, Manganese, and Potassium.
Limestone, marble, dolomite, calcareous sandstones and shale, and mafic igneous and metamorphic rocks contain high amounts of alkaline metals, such as those listed above and lower amounts of Aluminum. These alkaline metals produce higher pH in well developed soils.
Well developed and rich soil is created when dead organic matter is introduced into the soil and micro-organisms arrive to feed on the dead organic matter. As micro-organisms consume organic matter, they reduce organic molecules into mineral molecules and produce byproduct organic acids that react with and break down clays. This process releases metals bound to the clays, and the metals become mobile in the soil solution and available for uptake by living plants. Plants can absorb only mineral elements and compounds, so it is essential that soil formation processes reduce organic molecules and complex mineral compounds to simple mineral compounds essential for plant growth.
Soil pH Around Houses and Other Structures and Landscaping Issues
Site preparation for building usually involves grading and the loss of top soil. It is important to cache the topsoil portion for replacement after the building is completed. The building and subsequent slow weathering of structures that contain masonry effectively alters pH regimes around the building site, especially close to building foundations. The lime of masonry leaches into the soil and raises the pH. If the soils at the site are originally acidic, a new pH gradation regime is created during and after building construction. pH will be higher close to the structure and decrease away from the structue. Foundation plantings can therefore include calciphile (moderately acid to neutral) plant species. If acidophile (strongly acidic) plants such as azaleas are desired close to foundations, the cement increased pH must be buffered down using Aluminum oxide, Aluminum sulfate, or elemental sulfur. Cement patios, driveways, walkways, and masonry walls also affect soil pH upward.
Native Fern Soil pH Preferences
Strongly to Moderately Acid Soil Species: Osmunda Cinnamomia (Cinnamon Fern), Osmunda regalis (Royal Fern), Osmunda claytoniana (Interrupted Fern), Athyrium asplenioides (Southern Lady Fern), Thelypteris noveboracensis (New York Fern), Dennstaedtia punctilobula (Hay-scented Fern), Woodwardia areolata (Netted Chain Fern), Lygodium palmatum (American Climbing Fern), Dryopteris intermedia (Fancy Fern), Dryopteris campyloptera (Mountain Wood Fern), Woodwardia virginica (Virginia Chain Fern), Thelypteris kunthii (Maiden Fern), Dryopteris marginalis (Marginal Wood Fern), Asplenium montanum (Mountain Spleenwort), Asplenium pinnatifidum (Lobed Spleenwort)
Slightly Acid to Neutral Soil Species: Adiantum pedatum (Northern Maidenhair), Phegopteris hexagonoptera (Broad Beech Fern), Deparia acrostichoides (Silvery Glade Fern), Onoclea sensibilis (Sensitive Fern), Cystopteris protrusa, Dryopteris marginalis (Marginal Wood Fern), Dryopteris goldiana (Goldie's Wood Fern), Dryopteris celsa (Log Fern), Cystopteris fragilis (Fragile Fern), Matteuchia struthiopteris (Ostrich Fern)
Neutral Soil Species: Diplazium pycnocarpon (Narrow Glade Fern), Asplenium rhizophyllum (Walking Fern), Pellaea atropurpurea (Purple Cliff-brake Fern), Asplenium resiliens (Black-stemmed Spleenwort)
Cosmopolitan Species: Polystichum acrostichoides (Christmas Fern), Cheilanthes tomentosa (Wooly Lip Fern), Cheilanthes lanosa (Hairy Lip Fern), Asplenium platyneuron (Ebony Spleenwort)