Will My Strawberries Grow Next to Cedar Trees?

Cedar Family and Oils

• There are three divisions of the cedar family: true cedars (Cedrus spp.), junipers (Juniperus spp.) and arborvitae (Thuja spp.). Various parts of all these trees produce insect-repellent, volatile oils. Some species prefer acidic soil, while some do well in alkaline areas and others thrive in either acid or alkaline soils. Depending on the species, the oils extracted from or remaining in fresh cedar wood and mulch repel a variety of pests, including mosquitoes and clothing moths.

Allelopathy

• Trees that produce toxic substances inhibiting other plants' growth are allelopathic. One example unrelated to cedars is the black walnut (Juglans nigra), which contains the compound juglone in all its parts. Juglone is toxic to many plants, so they won't grow near black walnut trees. A 2009 copyrighted report from Washington State University Extension Horticulturist Linda Chalker-Scott, Ph.D., noted, "there is virtually no documented evidence for allelopathic activity in either Thuja or Cedrus spp."

Lack of Evidence

• Chalker-Scott said that Eastern red cedar (Juniperus virginiana) heartwood contains thujaplicin, a water-soluble compound that inhibits bacteria and fungi. This probably accounts for the wood's rot resistance, she reported, but in her survey of research literature she found no evidence that thujaplicin harms other plants. A separate article from the university suggests building a raised strawberry tower out of cedar wood.

Mixed Research Results

• In contrast to Chalker-Scott's report, a study by Justina Gray and Thomas Rosberg of Drake University found that Eastern red cedar's volatile oils might adversely affect some monocot plants, such as corn. However, the peas they tested, which are dicots, were not affected. Strawberries are also dicots, which are more highly evolved than monocots. The researchers noted that root-system differences may account for the corn being somewhat stunted when treated with a liquid in which Eastern red cedar foliage was leached. An earlier experiment conducted by University of Missouri Associate Professor Christopher Starbuck does not agree with the Drake University results. Starbuck considered whether cedar mulch harms plants. Using a leaching technique similar to Drake University's method, Starbuck tested germination of mung beans, rye grass and tomato seeds moistened with water in which he soaked mulch from an unspecified kind of cedar. Starbuck observed, "no obvious symptoms of phytotoxicity." He also found this to be true for seedlings watered with the mixture.