Rosemary trees have earned a reputation among gardeners for being finicky, turning from a healthy tree one day to a shrivelled brown fright the next. To save a dying rosemary tree or protect your healthy rosemary tree, you will need to strike a delicate balance between enough water and too much water, while providing the plant with sunlight and shelter from wind.
Examine your rosemary plant's growing conditions. In order to save your dying rosemary, you need to take all factors into account. There could be multiple reasons your plant is failing. How much sun does your rosemary receive in its present location? Is it exposed to wind? Do you notice any pests, mould or unusual growth on the plant or in the soil? Are your leaves turning brown?
Move your rosemary tree to a location where it receives direct sunlight, ideally for at least four hours per day. Rosemary plants do not fare well in shade or partial sunlight. If your plant has not been getting adequate light, this could save it.
Decrease the frequency and amount of your watering if your rosemary plant's leaves are turning brown. Rosemary trees like to be watered, but too much water will cause browning. Your rosemary plant may also be in a container that has poor drainage and this could cause root rot, which will kill your plant. Do not get moisture on the plant's leaves, since this may lead to disease.
Remove your rosemary tree from its container and replant it if you see mould on the soil, small bugs or other evidence of pests. When you remove the rosemary, compress the roots with your fingers to remove any old soil. If the roots appear brown and mushy, your plant has root rot. To save your rosemary, trim the roots back with scissors until the mushy parts are gone. Then replant your rosemary in a clean container using fresh soil.
Check the air circulation near your rosemary plant. If the plant is in a windy spot, it needs more protection from the wind. If your plant does not have enough air circulation, it may attract pests, fungus or bacteria that sicken it. Sometimes increasing air circulation (combined with more sunlight or better soil) can bring your rosemary back to good health.
Cut off diseased parts of the plant. If your rosemary tree is large, you can prune back the plant to encourage new growth. Stick healthy cuttings in a glass of water and plant them once roots have developed. This way, you have a backup rosemary plant if you are unable to save your rosemary tree.
Take your plant to a garden centre, botanical garden or horticulture program if none of these steps can help save your rosemary. Your plant may have a fungal or bacterial disease and someone at one of these places can advise you on how to treat your rosemary plant.