The reason rosemary becomes brown is due of root rot and fungal disease. The Mediterranean herb rosemary prefers dry weather. Overwatering, poor drainage, or humidity can result in persistently damp soils that are more susceptible to root rot, which turns rosemary’s leaves and roots brown.
Rosemary is a low-water-use plant that can withstand droughts. Instead of not enough moisture, too much moisture causes rosemary to become brown (sometimes with a withering appearance).
The following are the main causes of rosemary wilting:
- watering too much
- sluggish drained soils
- large rains
- extreme humidity
Continue reading to find out specifically why your rosemary is fading and how to fix the issue.
Table of Contents
Over Watering Causes Root Rot (Water Once Every two Weeks)
Overwatering, which causes root rot, is the most frequent cause of browning in rosemary leaves, roots, and stems.
Consider the herb rosemary, which is indigenous to Europe’s Mediterranean region.
Rosemary is frequently spotted growing untamed in this setting on rocky or sandy hill sides that drain swiftly after rains. Additionally, the area experiences rare rains and a dry heat with low humidity in full sun.
Rosemary has developed a special tolerance for these conditions and can survive in a severe, arid environment. As a result, the roots dislike spending a lot of time in wet soil.
Gardeners frequently overwater rosemary, which encourages the growth of fungi that cause root rot and other fungal diseases.
When rosemary is present,
- becoming dark, including the stems and foliage
- displaying signs of withering or drooping
The plant is then experiencing root rot as a result of overwatering and perhaps poorly draining soils. If root rot is not treated, the rosemary will probably die.
As soon as the rosemary starts to show any indications of going brown, reduce the watering.
- In dry weather, rosemary only needs water once every two weeks because it is drought-resistant. If there has been a lot of rain, wait until the soil is completely dry before watering.
- Winter is not the time to water rosemary because it will get all the moisture it needs from the environment. Due to decreased sun exposure, increased evaporation, and the plant’s more dormant state, rosemary is most susceptible to the fungi that make it turn brown throughout the winter.
When you do water rosemary, be sure to constantly give it a generous soak to help the roots to take root and ensure its drought tolerance. Light watering promotes shallow root growth, which harms the plant.
It could be hard to rescue the rosemary if it has substantially turned brown. Reducing watering can aid in the plant’s recovery if only a few of the bottom leaves are turning brown.
If the rosemary plant is already in a pot or container, I advise moving it to a new one with potting soil that has been supplemented with sand or grit to increase drainage and give the infected roots a chance to heal.
(For information on how to create the ideal watering schedule for your garden, read my post on how to water rosemary.)
Slow Draining Soils Cause Brown Foliage (Amend soils with sand or grit)
On hill sides with poor water retention, rosemary does best in well-draining sandy or rocky soils.
The root rot that causes rosemary to become brown is prevented by the remarkable drainage provided by the porous nature of sandy or stony soil. This helps keep the roots relatively dry.
In order to successfully produce rosemary in our gardens, it is crucial to mimic the original environment’s soil characteristics.
All that is necessary to accomplish this is either…
- builders’ sand or horticultural sand
- Agricultural tenacity
Both of which may be purchased online and in garden centers. The pore size in the soil is increased by the larger particle size of horticultural sand compared to other types of sand, which allows oxygen to enter the soil for root respiration and permits rain or water to drain away fast.
Effective drainage will keep the roots dry and free of illness, which could cause the leaves to turn brown.
It is a good idea to transplant the rosemary to a pot with roughly 20% sand or grit and 80% potting soil or compost if the rosemary was originally planted in clay soils, bogs, low lying regions of the garden, or in rich compost that absorbs water.
(Read my post on the ideal potting soil for rosemary.)
If your soil is thick clay, growing rosemary in pots might be an excellent option because they have better drainage than typical garden soils.
The best growing circumstances for rosemary will be produced by adding sand or grit to the soil, which will also enable the roots to dry out and heal.
It is a good idea to examine the roots while amending the soil and moving the plant.
It is a good idea to cut off the sick roots, stems, and leaves with a pair of sterilized pruners if any of the roots appear unhealthy (dark colored, maybe slimy roots as compared to healthier, lighter colored roots).
- To stop the spread of the fungus disease, wipe the pruners with a disinfectant-treated towel (of any kind) after each cut.
- Instead of composting the roots, get rid of them by burning or tossing them away to stop the fungus from spreading.
- Depending on how severe the fungal disease is, cutting the infected roots and stems will encourage new growth, and planting the rosemary in new soil—which is free of fungi—can help it recover.
(Read my post Why is my rosemary dying for more information on the causes of dying rosemary and possible remedies.)
Since excessive rainfall effectively mirrors the issues brought on by overwatering, it can be problematic.
Although rosemary may be produced in temperate regions with far higher rainfall than the Mediterranean, it is native to temperatures with less rainfall.
The secret to growing rosemary in areas with a lot of rain is to modify the soil before planting with a lot of sand or grit to provide good drainage, which will keep the roots dry.
Due to the pots’ superior drainage, rosemary can be grown in pots and containers rather than garden soil in locations with heavy rainfall.
Moving the pot under cover for a few days until there is more sunny weather is advised if the rosemary is going brown after prolonged periods of rain. This will help the soil to dry out and the rosemary to recover.
If the rosemary was originally planted in garden soil, it might be required to move it to a pot with potting soil that has been supplemented with sand or grit since quick drainage will help to lessen the effects of heavy rain.
Humidity Causes Brown Leaves
Another factor contributing to the browning of your rosemary plant is humidity.
Rosemary does best in open areas and tolerates a good breeze blowing through the foliage, which keeps the plant dry and lowers the risk of fungus that can cause the leaves to turn brown.
Consider the microclimate if your rosemary is grown in a pot or other container. A more humid environment might be created for the rosemary in pots that are placed in patio corners or perhaps are surrounded by other plants that are too close.
Larger rosemary plants should be spaced out by around 2-3 feet. This area provides a better opportunity for airflow around the leaves, resulting in a dryer atmosphere.
If you are planting rosemary in garden borders, I would also advise you to plant them around 2-3 feet away from any other plants.
Additionally, this will make sure that each rosemary has enough space for the roots to spread out and not have to compete with other plants for water, nutrients, or space, allowing the rosemary to remain healthy and disease-free.
With a pair of pruners, remove any brown leaves from plants that have experienced frost damage. This encourages new development, and the plant should recover. But if any additional cold spells are anticipated, I advise you to cover the rosemary plant.
You only need to bring the rosemary plant indoors for the evening if it is in a pot, possibly in the garage if there is room.
If the rosemary is instead planted in garden soil, it is preferable to protect it from frost by covering the plant with fleece or a cloche, which is surprisingly effective.