Bay leaf (Laurus nobilis) is an evergreen tree native to southern Europe that has been adapted to regions all over the world. Bay leaves were made into wreaths that were worn by ancient Roman poets, scholars and athletes as a symbol of wisdom and glory. The Latin meaning for Laurus is praise and the meaning for nobilis is famous. Bay trees grow to 18 to 60 feet high depending on the variety with up to a 12-foot spread. Bay leaves are used to add flavour to soups, stews, stocks and sauces, as well as fish and vegetables.
Bay trees thrive in soils that are rich, moist and well-draining. Add mulch around the base -- being careful not to make contact with the trunk -- to help retain moisture and protect the roots from cold winter weather. Bay trees prefer full sun, and are not very hardy in the North. Fertilize during the active growing cycle with a balanced fertiliser. Reduce feedings and waterings during the winter months.
Bay trees have shallow roots, which make them susceptible to frost damage. Bay trees also need protection from strong, cold winds to avoid scorched leaves. This is especially important for bay trees 2 years or younger. During particularly harsh winters, the leaves may turn brown, but will return to green in the spring. Although bay trees are not cold hardy, Northern gardeners can still enjoy them by planting the tree in a container and moving it to a warmer area during the winter. Use containers with adequate drainage and repot as the tree gets bigger to avoid the roots becoming pot-bound.
Bay trees are susceptible to sooty mould, a black, powdery fungi that grows on honeydew which is excreted onto the leaves by plant juice-sucking insects. Sooty mould blocks the leaves from receiving sunlight, which blocks photosynthesis. The best control method of sooty mould is to control the insects that are excreting the honeydew. Wiping the leaves with a solution of soap and water helps to remove the existing mould.
Scales are the main honeydew-excreting culprits that grow sooty mould on bay trees. Scales fall under three main categories: armoured, soft and mealybugs. They all cause damage by sucking plant juices from the bay leaves, which causes leaf yellowing, leaf drop, branch dieback and death. Look for scales on the undersides of leaves and on stems. Prune off any infested tree parts and decrease the number of plants around the bay tree to encourage better air circulation and reduce humidity. Decrease nitrogen because scales breed and have better survival on plants high in nitrogen. Use beneficial insects like ladybird beetles, green lacewings and parasitic wasps that prey on scales. Horticultural oils are also efficient at killing scales at all stages of the life cycle.
Bay suckers also ruin the appearance of bay leaves by sucking the sap and causing the leaves to thicken, curl at the edges and turn yellow and then brown. Check the leaves' undersides and the curled edges for small, greyish-white insects. Prune off infested leaves and apply a systemic insecticide like neem oil to control the pests.