Rosemary, a Mediterranean plant, prefers dry conditions. Root rot is a condition where rosemary roots and leaves turn brown due to persistently damp soils, whether they are caused by overwatering, slow drainage, humidity, or excess watering.
Rosemary, which is drought-resistant, doesn’t need much water. Rosemary can turn brown due to too much moisture around its roots.
The biggest risk factors that rosemary will turn brown are
- Over watering
- Slow draining soils
- High rainfall
- High humidity
Continue reading to find out why your rosemary is turning brown, and how to fix it …
Root Rot Caused by Overwatering (Water once every two weeks )
Overwatering can cause root rot, which is the most common reason rosemary stems, roots, and leaves turn brown.
Remember that rosemary is a native herb to the Mediterranean region .
In this climate, rosemary can be found growing wild on the rocky hillsides that drain quickly after rain. The climate is dry with high humidity and low rainfall.
*Rosemary is adapted to this environment and can thrive in harsh, dry environments. The roots don’t like being in damp soil for prolonged periods of time.
Gardeners often overwater rosemary, which can lead to root rot and other fungal disease.
If your rosemary plants is:
- Turning brown, with foliage and the stems
- Drooping or wilting in appearance
If the root rot is severe, it could be due to excessive watering or slow drainage soils. If left untreated, root rot can cause the death of rosemary.
Reduce the amount of watering once you see signs that the rosemary is turning brown.
- Rosemary can withstand drought but only needs water every two weeks in dry conditions . If there has been significant rainfall, it is best to wait until the soil is dry before watering.
- Don’t water rosemary in winter as it will get all the water it needs from the environment. Rosemary is more susceptible to fungal diseases in Winter because it will be less exposed to sunlight and evaporation, and become browner.
Always water rosemary with a good soak. This encourages roots to grow and ensures drought resistance. A weak plant will result from too much watering.
It is possible to save rosemary that has already turned brown. If the rosemary is browning in large quantities, it may be difficult to save. However, if the plant has only a few brown leaves, then you can reduce the watering.
If the rosemary is still in a container or pot, I suggest that you transfer it to a new container with a potting mixture that has been amended with sand and grit. This will improve drainage and give the roots a chance to recover.
(Read my article how to water rosemary for how to establish the optimal watering schedule for your garden).
Slow-Draining Soils Cause Brown Foliage. (Amend soils using sand or gritty )
It’s just as important to ensure that the soil drains fast as it is to water rosemary properly in order to fix rosemary that has turned brown.
Rosemary thrives on well-draining soils, sandy or rocky soils that drain well and are located on hillsides that don’t retain water very well.
The porous structure of sandy soil or stony soil permits for exceptional drainage, which aids in keeping the roots relatively dry. This prevents root rot, which causes rosemary to turn brown.
To grow rosemary well, it is essential to recreate its natural soil conditions in our gardens.
This is easy to do, you just need …
- Horticultural or builders sand,
- Horticultural grit
…both are available at garden centres and online. Horticultural sand is larger in particle size than other types of sand. This allows for oxygen to enter the soil and allows water to run off quickly.
A good drainage system will ensure that the roots stay dry and is free of disease, which can cause browning.
If the rosemary is planted in clay soils, boggy or low lying areas of the garden or in rich compost that retains water then it is a good idea to transplant the rosemary to a pot with around 20% sand or grit and 80% potting soil or compost.
(Read my article, best soil for rosemary in pots).
Pots are more suited to drainage than most garden soils. They can be used to grow rosemary, especially if you have heavy clay soil.
Adding sand to the soil will help rosemary grow and the roots can dry out.
While amending the soil or transferring the plant, it is a good idea for the roots to be inspected.
If any roots appear unhealthy (dark roots that look slimy, as opposed to healthier, lighter roots), it is a good idea for you to trim the affected roots, stems, and leaves using sterilized pruners.
- Use a disinfectant-treated cloth to clean the pruners after each cutting to stop the fungal disease spreading. Throw away the roots or burn them to prevent the fungus from spreading. The pruning of diseased stems and roots will encourage new growth. However, this is dependent on the severity of the fungal infection.
(To learn more about the causes of dying rosemary and for the solutions, read my article why is my rosemary dying? )
High rainfall can cause problems, as it mimics overwatering.
Rosemary is a native of climates with less rainfall, but it can still grow in temperate climates with more rainfall than the Mediterreanean.
To grow rosemary in areas with high rainfall, you need to amend the soil with lots sand or gravel to ensure drainage. This will allow the roots to dry out.
Pots and containers can be used to grow rosemary in areas with high rainfall. This is due to their better drainage.
If the rosemary has turned brown from heavy rains, I suggest moving it under shelter until more sunshine is available to let the soil dry out.
If the rosemary was planted in garden soil, it might be necessary to transfer it to a pot that has a potting mix. This will allow for fast drainage to reduce the effects of persistent rain.
Rosemary is native to the Mediterranean with hot summers and mild winters. It is not a particularly cold hardy plant (hardy to USDA zones 9) and the newer growth in particular is vulnerable to frost damage.
For plants with frost damage, remove any brown leaves using a pair pruners. This stimulates new growth. The plant will recover. If there are more cold snaps, I recommend protecting the rosemary plant.
If the rosemary is already in a pot, you can simply bring it indoors to enjoy the evening.
If the rosemary is grown in soil, then cloches or fleece can be used to shelter it from frost. This is surprising effective.
Humidity Causes brown Leaves
Humidity could also be a reason your rosemary plant turns brown.
Rosemary thrives in open areas and can tolerate a breeze through its foliage. This helps keep it dry and lessens the risk of fungal diseases that could turn the leaves brown.
If your rosemary is in a container or pot, you should consider the microclimate. Pots placed in the corner of a patio, or surrounded by plants too close to it can make the environment more humid for the rosemary.
For larger rosemary plants, keep pots and containers at least 2 feet apart. For a dryer environment, this space will allow for more airflow.
If you grow rosemary in garden borders, I recommend that they be planted at approximately 2-3 feet from other plants.
This will ensure that rosemary roots have enough space to grow and that other plants don’t compete for nutrients, water, or space. The rosemary will be healthy and free of disease.
- Root rot causes rosemary branches and leaves to turn brown from fungal disease and root rot. Root rot occurs most often due to overwatering, excessive rainfall, high humidity, or slow-draining soils. To prevent rosemary from turning brown, reduce the frequency of watering by adding sand or gravel to the soil. This will improve airflow and protect potted plants from excessive rainfall. If the rosemary is suffering from extensive root rot, you should remove the rosemary and trim the brown leaves and infected roots. Place the rosemary in a new pot, with amended potting soil with sand and grit. Water once every two weeks.
- Rosemary does not always recover depending on the extent of the root rot but by following the best practices of care and replicating the natural Mediterranean environment in which rosemary thrives (with sand and infrequent watering) then the rosemary has the best chance of recovery so that the leaves are a healthy green rather then brown.