Clay Soils: Curse and Blessing

Clay soil tends to be poorly drained. It retains water, and therefore remains cold later into the Spring than properly drained and aerated soils. It is also dense, which may limit the ability of some plants to force their roots through it. Furthermore, because of the lack of aeration in clay soils, useful bacteria (cellulolytic and nitrogen-fixing) are restricted to a narrower layer of activity. When such soils are underdrained, the plant roots can penetrate more deeply and the bacteria can thrive in a broader layer—returning more nitrogen to the soil.

Because clay soil remains cold longer in the spring, it may allow some plants to survive further north than they could in aerated soils. A plant, such as Rosa arvensis, will be less anxious to sprout in the Spring when its roots are stuck in cold, clammy soil, and thus may escape most late frosts. Allen: Rosa arvensis, a problem Wild rose (1987). Thus, clay soil, particularly on a north-facing slope, might allow plants of border-line hardiness to survive.

Plants that are adapted to clay soil have root caps that fit over the root tips like gloves over fingers. They can push through dense clay. Other plants, adapted to looser soils (sand or humus) may have smaller root caps that provide little protection, because little is needed. (Fitch, 1913) This also happens when plant breeders raise their seedlings in loose soil, and thus (however inadvertently) select for intolerance of clay soils.

As Hannibal (1943) noted, "Amaryllis Johnsonii is also quite hardy and will do well in outdoor locations, even in heavy clay soils." However, more highly developed varieties of later generations commonly lose the ability to thrive on heavy clay. "Soil that tends toward a concrete-like consistency when dry is fatal. Amaryllis do not have hairy roots that push through hard materials after moisture. Unless the soil a soft and friable at all times, the thick, fleshy roots the amaryllis will just lose their enthusiasm for growing and be content to survive as a little bulb with a few leaves until conditions change." (Linsted, 1961)

Correcting the problem of clay, when it is a problem, may be as simple as raising the soil level for plants that need earlier warmth, and are able to withstand whatever frost may come. A more permanent solution suitable for large areas is to install drainage tiles to carry away the excess water. As aeration improves, more plants will be able to send down their roots, the soil will soften and bacteria will thrive in a deeper layer.

Tull: Climate changes plants (1751)
... and some Land, retaining Water longer, is colder; some, suffering it to pass down quicker, and by the Nature and Figure of its Parts, causes such a Refraction and Reflexion of the Sun's Rays, which give a great Warmth, as in Sand, and gravelly Grounds, that are well situate, and have an under Stratum of some Sort of hollow Matter, next under the Staple, or upper Stratum, wherein the Plough is exercised.

Miller: Drains (1759)

Wempey: Draining Land (1775)

Monk: Under-Draining (1794)

Scots Magazine: Draining Land (1799)

Tuke: Soil Improvements (1800)

Johnstone: Hollow-Draining (1801)

Monthly Genesee Farmer: Draining Lands (1838)

Allen: Underdraining (1846)

Wiggins: Underdraining (1847)

Johnson: Composition of Land Drainage Water (1850)

Genesee Farmer: Under-draining and experiments (1852)

The Florist: Under-draining (1853)

Country Gentleman: A Few Words on Underdraining (1855)

Owen: Underdraining in Kentucky (1857)

Agr. Jour. Cape of Good Hope: Drainage (1863)

Tiffen: The Modern System of Draining (1865)

Meehan: Do Plants Need Water? (1875)

Davie: Underdraining in Kentucky (1878)

Saunders: Draining land in dry regions (1883)

"Single Handed": Earth Temperatures (1883)

Ratliff: Draining Tiles (1884)

Walker: Drainage in Vermont (1884)

Divers, etal.: Burnt Earth (1891)

Rennie: Underdraining (1900)

Billingsley: Undrainage for soil improvement (1904)

Storrs Agricultural Experiment Station Bul. No. 62 (February, 1910)
C. D. Jarvis: Apple Growing in New England
Underdraining. The work of preparing land for orcharding becomes very expensive where underdraining is necessary. In view of the abundance of suitable orchard land, it would seem unwise to select for the purpose land that requires to be underdrained to any great extent. Occasionally, however, a small area in a large tract will be found to be springy, and to avoid open spaces in the orchard, should be underdrained. The apple, like most fruits, will not thrive on wet soil. It is not necessary to go into the philosophy of underdraining at this time. It is enough to say that for apple orchards the drains need to be about fifty feet apart, and should be comparatively deep to prevent their being clogged by the roots of the trees.

Miles: Land Draining (1911)

Bowman: Influence of Water on Soil Temperature (1911)

Burbank: Drainage (1914)

Jones: Draining and Soil Temperature (1916)

Pemberton: Drainage for Roses (1920)

Fippin: Development of Under-Drainage (1921)