Many others, including the Croatian study cited earlier, have found thyme to be very effective against mold, more so than many other oils tested. The Croatian study also found that an extract of thyme oil called thymol was even more effective than thyme oil itself, suggesting that other plants containing thymol are probably effective. Oregano is another source of thymol, so it is no surprise that oregano often tests strongly against mold. The tropical plants cinnamon, clove, and lemongrass also show up in study after study as being effective against a variety of molds. In fact, in a study from India17 testing 75 essential oils against Aspergillus niger, the researchers concluded that the most effective were cinnamon, cassia, clove, and lemongrass.
Among the most impressive are caraway, lemon basil, oregano, bay (Pimenta racemosa, not to be confused with bay laurel, which is another plant), thyme, cinnamon (both leaf and bark of Cinnamomum zeylanicum, which is true cinnamon, though cassia, which is often substituted for cinnamon, is also impressive in this regard), clove, and lemongrass. These are my top picks. Some others such as lavender, eucalyptus, tea tree, and rosemary can pinch-hit, but they don’t test as strongly as the others.