Rosemary is a perennial aromatic herb, valued for its hardy, rustic nature. Formerly known as Rosmarinus officinalethe name has been changed to Salvia rosmarinus due to its growth habits closely related to wise sex.
Native to wild coastal habitats in southern Europe, it is used for dry summers and mild, wet winters. However, as a popular culinary herb, it is grown almost everywhere in the world in full sun with light, well-drained soil.
If your rosemary is showing signs of stress, identify the cause on this list and apply the appropriate remedy to restore your plant’s health.
Related Reading: How to Propagate Rosemary
Overwatering rosemary literally chokes the roots. Watch out for leaf tips turning brown. Often it is thought that this is due to a lack of water, but in this case it is the opposite problem.
When you see the leaves turning brown, the first thing you usually do is water more. But this actually causes the roots to die, causing the root to rot. As too much water is administered, more and more leaves and branches turn brown and then black.
Stop watering the plants and let the soil dry out completely before watering again. Provide adequate drainage for plants in their current location. It may be necessary to move them and replace the soil to improve drainage.
For container-grown rosemary, make sure the soil dries out between waterings and water drains through the drainage holes in the bottom of the container.
You can test the ground by driving a wooden dowel into the ground. If it comes out dry, it’s time to water.
Waterlogged rosemary also causes the leaves to turn brown. But unlike excess water, plants become twigs and dry out.
The solution is to add water and soak the plant well. Cut off any brown dry spots and feed the roots with a liquid kelp fertilizer to help the plant recover.
Do this weekly for two weeks and you should see new growth appear.
3. Bad background
Heavy clay soil is not good for rosemary and causes problems with waterlogging and root rot. It also compacts easily, preventing oxygen from reaching the roots.
In these cases, add plenty of organic matter or coarse sand to the soil before planting to improve drainage. If the plants are already in heavy clay soil, they should be dug up and moved or planted in pots or raised beds where the soil can be easily amended by adding things like perlite to the potting mix.
Rosemary prefers the fairly poor, calcareous or stony and sandy soils of its natural habitat, but it tolerates most soils except heavy clays.
4. Incorrect pH
Rosemary prefers slightly acidic to neutral soils with a pH between 6.0 and 7.0. Most garden soils have a similar pH. If the pH is too acidic, the rosemary will react by turning yellow and dying.
Acidic soil prevents the roots from absorbing nutrients, which stresses the plant and turns it yellow. An inexpensive soil test probe determines soil pH so you can make appropriate adjustments.
5. Insufficient light
Rosemary needs to be planted in full sun for it to grow well. The shade prevents the soil from drying out sufficiently, highlighting the problems associated with overwatering.
If the foliage begins to turn yellow, it could also mean that the plant is getting too much shade and needs to be moved.
Rosemary needs at least 6 hours of sun per day, but up to 8 hours per day. Less will have an effect on the health of the plant.
6. Incorrect temperatures
Rosemary likes a bit of heat and mild winters. They are not hardy and must be protected from frost in winter. Also, cold, wet soil will quickly rot and kill the plant. If the temperatures are too low or there is frost, the plants will die quickly and will need to be replaced.
If the temperature in your area drops below 30F, grow rosemary in containers on a sheltered patio or bring it indoors for the winter. Rosemary prefers temperatures between 55F and 80F.
7. High humidity
Rosemary grows naturally on windy coastal slopes. In these areas there is an average amount of moisture. Too much moisture around rosemary slows evaporation and can lead to fungal diseases and root rot.
Ensure adequate air circulation around the plants and prune as needed. Humidity should be around 45% to 55% for the best possible growth.
8. Root rot
Root rot occurs when there is too much water around the roots of the plant. A fungus, or more specifically a parasitic water fungus called a pythium, attaches itself to the roots and causes them to rot.
Change your watering schedule immediately if you see plant parts turning brown, drooping, or wilting. In severe cases, it is best to uproot and dispose of the plant before it can infect other plants in the area.
If detected early enough, damaged roots can be cut off, leaving enough healthy growth to propel the plant. Replant in fresh potting soil with adequate drainage for storage. You can also treat the plant with an appropriate commercial fungicide to remove any traces of the problem around the roots.
Although not common, rosemary can attract pests such as aphids, spider mites, whiteflies and bedbugs when stressed. If the foliage dries up and falls off the stems, these sucking insects should be dealt with quickly.
Aphids are one of the most common and easily identified pests, and they usually attack new growth. They are usually motionless and easy to see. They suck the sap from plants, causing them to wither.
Mites are small, recognizable by the dust and cobwebs they leave behind. They also suck sap from leaves and stems, making the plant weak and sick.
Whiteflies look like small moths, which makes them quite easy to identify. They can fly off the plant during treatment, so it’s important to keep an eye out for new infestations.
Bedbugs are known for the frothy substance they leave behind after sucking on rosemary leaves. They are small and related to aphids, but are easily identified by their moss.
Minor infections can be controlled by removing the pests from the plant. You can also try neem oil or an insecticidal soap and monitor the plants to see if an infestation returns.
10. Powdery mildew
Powdery mildew is a type of fungus. It can be identified on plants as a powdery white or gray growth that covers the leaves, stems, and fruits or flowers of a variety of plants.
Rosemary plants with poor air circulation, too much shade, too much water and inappropriate temperatures can be infested with these spores. Although it doesn’t kill a plant, powdery mildew causes curled or yellowed leaves, droopy leaves and distorted flowers.
Check the undersides of the leaves for the first signs of white powder and remove any infected areas. Make sure the plant gets enough sunlight to improve evaporation. Prune to improve air and water circulation at soil level instead of wetting the leaves.
You can use a commercial fungicide to treat the plants, but be sure to follow up as it may take several applications before the problem is eradicated.
11. Lack of size
In general, rosemary can survive without regular pruning. However, the back branches may need pruning to improve air circulation and prevent pests and fungal diseases from attacking the plants.
They respond well to pruning and harvesting for the kitchen and can even be shaped and hedged.
12. Too much pruning
Other than the usual harvesting and aeration of the plants, no pruning should be done for 6-8 weeks before the average frost date for a region. Pruning at the wrong time of year, or over-pruning, will damage plants to the point where they may not recover.
When pruned in late winter or early spring, the plant can be pruned up to a third of its size. But, as with all woody plants, you should leave some foliage on the stems and never prune past older woody stems. No new stems grow on the old wood.
A surefire way to kill a plant quickly is to prune it back until it has bare stems. Fertilize soon after pruning to support new growth.
Here’s our complete guide to pruning rosemary for tall, bushy plants.
13. Nutritional Imbalance
Although not common, the leaves can turn yellow if the plant lacks nitrogen. Fortunately, the solution is simple: give a fertilizer rich in nitrogen. Treat immediately with a liquid fertilizer and/or a handful of slow-release, high-nitrogen granular fertilizer around the base of the plants.
If the leaves are falling off and growing vigorously, you may have a problem with too much nitrogen. Excessive growth will be more susceptible to pests and diseases. Rinse the soil and stop feeding for a while to fix the problem.
14. Improper Fertilization
Although rosemary is grown in an area with sandy, chalky soil, it generally does well with a little extra feeding.
Feed with a general purpose fertilizer during the growing season and do not feed in the winter.
Under-fertilization can be clearly seen in yellowed leaves, while over-fertilization can be seen in stunted growth and leaf discoloration. In these cases, reduce feeding to once a year and always follow the instructions on the package.
Rosemary doesn’t like crowds. Plants that are too close together compete for root space, causing their roots to tangle and compete for nutrients and water. This will limit the growth and health of both plants.
Remove plants that are too close together and plant them elsewhere in your garden or move them to containers. Prune to ensure good air circulation to avoid attracting pests and diseases.
If you are growing a hedge, space the plants 18 to 24 inches apart and make sure they are trimmed regularly to control foliage and improve air circulation between the branches.
Related Reading: 10 Rosemary Companion Plants (And 5 That Shouldn’t Be Anywhere)
16. Lack of space for pots
Potted rosemary will be soft and slow growing. The lower leaves may also turn yellow.
You can test this by slowly emptying the plant from the pot to check for roots. If the roots are near the edge of the pot, they should be transplanted into a larger pot with fresh potting soil.
Remember to gently comb the roots from below to prevent them from growing in circles.
With proper care and awareness of potential problems, you can keep your rosemary healthy all year round. Check regularly for signs of trouble to fix the problem before it finally kills your plants.