Do you love growing rosemary indoors or outdoors, but lately have run into an issue of your rosemary turning black? In this post, you will learn about rosemary turning black (plant or tips, needles, cuttings turning black), the main causes of rosemary turning black, and solutions, whether you can eat black rosemary and answers to some frequently asked questions.
There are many factors that can lead to your rosemary turning black, and include:
- Overwatering (the most common cause of rosemary turning black)
- Over-head watering
- Soils that are slow draining
- High rainfall
- High humidity
- Insects and diseases
- Lack of natural light in outdoor farming
- Low artificial light in indoor growing
These factors lead to root rot (fungal infection), black spot formation, botrytis, and other fungal infections. Fungicides might be required to treat those diseases. However, you must be careful using toxic chemicals, especially if growing rosemary for consumption. Read more about rosemary diseases and pests here.
Rosemary is a perennial evergreen flower that is adapted to sandy and stony soils. It grows well under high draining soils, 10-12 hours of sunlight with little rainfall, and moderate watering.
The first section of this article gives full insight into factors that can cause your rosemary to turn black. The second section is related to scientifically proven possible solutions, and the third section gives a good insight into frequently asked questions.
Reason 1: Overwatering
Rosemary is native to the Mediterranean region. The soils of the Mediterranean region consist of a mixture of stony and sandy soils. This region receives low and infrequent rainfall with lots and lots of sunshine throughout the year.
This shrub grows robustly in well-drained dry soils and is drought resistant. Most gardeners overwater their rosemary garden, which leads to fungal infection and eventually root rot.
Root rot and fungal infection can be a cause of the foliage section of rosemary turning black. Overwatering can be detrimental to rosemary and must be avoided to keep your rosemary fresh.
Reason 2: Over-head watering
The second possible cause of your rosemary turning black is over-head watering. Over-head watering leads to mildew (a form of fungus) and dark leaf spots. Both mildew and dark leaf spots can make your rosemary turn black.
The other problem associated with over-head watering is that the spores of mildew spread throughout the plant by sprinkling water over the leaves. It is the best practice to apply water at the base of this shrub every 2 to 4 weeks.
The rate of evaporation remains high during the summer season. During hot periods, overwatering does not pose a serious problem if compared to colder seasons. However, in winter, where the rate of evaporation is low, overhead watering leads to fungal infection and turns rosemary black.
Therefore, over-head watering must be avoided to limit the chances of rosemary turning black. To maintain fresh rosemary, you must be watering at the base, where most of the water reaches the root section and chances of fungal infection are reduced.
Reason 3: Soils that are slow-draining
The third most probable cause of your rosemary turning black is soil those are slow-draining. As mentioned earlier, rosemary originated and evolved in the Mediterranean region. The soil of this region is well-draining, sandy and stony.
For proper growth and development, and to avoid this shrub turning black soft high draining, sandy and stony soils must be used.
When you grow it in rich compost and clay soil (both slow draining), it can cause your rosemary to rot and turn black. The reason behind it is that the rich compost and clay soils retain lots of water in the root section. The moisture in the root section leads to root rot and fungal infection. Both root rot and fungal infection lead to your rosemary turning black.
Reason 4: High rainfall
You may live in a region where your outdoor garden receives high rainfall. High-rainfall leads to soil getting wet. Wet soils, in return, lead to root rot and fungal infection. More frequent rainfall is also associated with your rosemary turning black. Make sure to water your rosemary much less if you get lots of rainfall, around once in 3 weeks or so.
Reason 5: High-humidity
Yes, you read it right. High humidity has a direct relation with your rosemary turning black. As discussed earlier, rosemary is adapted to regions where it receives little and infrequent rainfall with high sunlight and low humidity.
The following are the main determinants of high humidity:
- When row to row and column to column distance is not properly maintained between rosemary shrubs.
- Over-crowding of rosemary shrubs.
- Low fresh air flow between the leaves and shrubs.
- Not maintaining adequate spacing between rosemary shrubs.
These factors play a key role in high-humidity, which causes root rot and fungal infection, eventually the foliage turns black, and shrub dies. If growing rosemary indoors, make sure to provide adequate air ventilation and bright light (especially to seedlings, which are more prone to diseases).
Reason 6: Insects and pests
Spiders, mites, mealybugs, whiteflies, thrips, and many others are the major insects and pests of the rosemary plant. They can also cause the weakening of the rosemary plant, turning it black. These insects and pests leave behind honeydew and other substances, which lead to the formation of molds.
Make sure to always look for insects and pests on your plant and treat them, before they damage the plant. For example, to get rid of mites, aphids, whiteflies and other soft-bodied insects using non-toxic solutions, you can use insecticidal soap like this. You can also use horticultural oil like this one and neem oil. Insecticidal soap will paralyze soft-bodied pests and kill them, as it contains fatty acids. Neem oil contains azadirachtin, a powerful repellent against pests. Horticultural oils contain mineral oils for effective pest control.
Avoid using strong pesticides for treating your rosemary, especially for consumption. Only concentrate on the natural remedies discussed above. Avoid using pyrethrum, rotenone, ryania, pyrethrin, sabadilla, and similar toxic pesticides.
Read all about rosemary diseases and pests here.
Reason 7: Low Sunlight
Sunlight plays a huge role in the photosynthesis of all plants. Through photosynthesis, plants receive their food and energy. Rosemary is a high sunlight-dependent shrub. It requires at least 10-12 hours of daily sunlight for proper growth and development of rosemary.
Low light conditions over a long period of time can lead to turning your rosemary black. Moreover, low sunlight over a long period of time leads to the shedding of needles. Eventually, the whole rosemary dries out.
Reason 8: Extreme cold
As mentioned above, rosemary is native to the Mediterranean, with hot summer and milder winters. So, if you live somewhere with cold winter and you have a rosemary shrub outdoors, it might be a problem. Your rosemary might weaken due to colds and high humidity, start turning black and even die. Rosemary isn’t very resistant to cold and frost, so you might need to protect it in the winter.
If you get below freezing temperatures (around 20 F/-7 C), you must protect your rosemary (if outdoors). The main goal is to protect it from harsh winds and cold. To protect your rosemary, make sure to plant it in an area of the garden that doesn’t get too much wind.
Also, add around 3 inches (7.5 cm) of mulch onto the soil, towards the middle of autumn. And if temperatures get much lower than below freezing, you can cover your rosemary with a horticultural frost cover like this. This will help protect it from the detrimental effects of cold. Make sure that cover doesn’t block air circulation.
Rosemary turning black – solutions
- Root rot fungal infection, black spot formation, botrytis, and other fungal infections must be treated with high quality and eco-friendly fungicides.
- To avoid overwatering, experts suggest watering the rosemary plant every 3-4 weeks in summer. During the winter period, avoid watering rosemary because the plant receives water from the environment.
- Agriculturists and gardeners suggest that water must be applied at the base, where it is taken up by roots.
- You must avoid slow draining soils for growing rosemary. Go for sandy and stony soils instead. You can use a mixture of 20% of sand and 80% multipurpose compost.
- Row to row distance of at least 3 feet must be maintained to avoid overcrowding of rosemary (if shrubs) and high humidity.
- To avoid the negative effects of high humidity, the rosemary pots must be placed in a place where fresh airflow is adequate.
- Eliminate and remove insect and pest-infected leaves as soon as possible to avoid your rosemary turning black. Then treat your rosemary shrub preferably with natural controls, such as neem oil, horticultural oil, or insecticidal soap like this.
- Your garden/indoor placing spot must be in such a place where there is 10-12 hours of sunlight.
- Experts suggest light pruning of your rosemary plant during spring and late fall, to avoid any chances of over-crowding.
- Always use porous clay pots instead of plastic pots for growing rosemary in indoor or outdoor gardens.
- You must always check for insects and pest presence while buying rosemary shrubs.
- Fertilize the soil around once a month, or at least once in two months to boost the growth and development of rosemary.
Why are rosemary tips turning black?
If your rosemary plant’s tips (needles) are turning black, you might have overwatered your rosemary. Please remember that rosemary is extremely drought tolerant, and you should always let the soil dry completely before watering again. Avoid placing any stones on the soil as it can prevent proper drainage.
However, if your rosemary’s tips are turning brown and look shriveled, it might be suffering from heat stress and might need watering. Also, your rosemary might be suffering from a shock if you have just repotted it or changed its location/environment drastically.
Why are my rosemary cuttings turning black?
If your fresh rosemary cuttings are turning black, there might be a few main reasons for that. The main reason for a rosemary cutting to turn black is overwatering and lack of drainage. Make sure a pot has drainage holes, and don’t water until soil dries out.
Frequently Asked Questions (FAQs)
Can you eat rosemary with black spots?
This is the most common problem observed in rosemary. The black spots on the shrub are due to fungus. The consumption of rosemary with black spots does not harm the body in general, but make sure to wash it properly before eating. However, people who are allergic to fungus must avoid even touching rosemary with black spots, let alone eating it.
Why does rosemary turn black in the fridge?
One of the reasons why rosemary is turning black in the fridge is because the plant already contained fungus spores. Fungal spores in wet conditions give rise to black spots, when you keep rosemary in the fridge.
To counter this problem you can try to dry the rosemary in direct sunlight first. Remove all the foliage from stems. Then use a glass jar to store it and cover it with a lid. In this way you can save your plant from turning black in the fridge.
Can you eat black rosemary?
Yes, you can eat black rosemary, but it is not advisable, because it loses much of its aroma. Black rosemary is also not very appetizing, when compared to fresh or dried rosemary without black spots.
When does rosemary expire?
Fresh rosemary expires in 10-14 days on average. First, the leaves will expire within 10-12 days, and then stems – in 12 to 14 days if you keep rosemary in cool and dry conditions.
To avoid wasting fresh rosemary, most gardeners opt for using and storing dried rosemary. Both dried and grounded rosemary lasts up to 3 years depending on storage conditions.
Does rosemary go dormant?
It is an evergreen herb. Rosemary goes dormant during winter season, when its growth and development stops up to 90%. The dormant phase finishes with arrival of the spring season.
What is the best season to cut rosemary?
The best season to cut and prune rosemary is winter.
Can rosemary survive frost?
The minimum optimal temperature for rosemary to grow and thrive is 30*F (-1 C). Below this temperature the shrub growth and development is seriously affected. When the conditions are freezing (such as during frost), it is advisable to bring your flower pots indoors to avoid any kind of loses.
Is rosemary harmful for cats and dogs?
According to the reports of ASPCA, rosemary does not pose any risk to cats and dogs. However, it contains certain volatile oils that can cause stomach problems and depression in animals such as cats and dogs. Naturally, cats avoid rosemary due to its aroma.
What is rosemary good for?
Rosemary is natural painkiller for muscle cramps and joint pains. Additionally, the oil of this plant helps in preventing baldness and increases hair growth. Furthermore, when used with tea or water it helps in reducing headaches, digestion problems and reduces stress. And of course, rosemary is a herb widely used in cooking.
Is rosemary good for pregnant women?
For breastfeeding mothers and pregnant women, it is a best practice to avoid any form of contact with rosemary. That’s because it can increase blood pressure and possibly stimulate blood flow around the uterus.
How do you use rosemary for healing?
Since prehistoric times rosemary has been used for aromatherapy and physical healing.
- Candles with rosemary help in staying focused
- Homemade soups are used for aromatherapy
- Rosemary shrub is also used in a pot of boiling water for reducing stress
Where can I grow my rosemary?
When rosemary is grown indoors, in pots, then it is advisable to grow them on south facing windowsills. That’s because this spot receives lots of sunlight during winter and summer. If natural sunlight is generally low, then you can also use artificial light with the help of special light bulbs.
Rosemary is easy to grow from small plants that you can take indoors from a garden or buy from a garden store. Check for pests before you take your rosemary home or indoors from the garden.
Is rosemary oil good for skin and hair?
Rosemary oil contains a certain organic substance that helps in hydrating and controlling the production of oil on the skin. It also helps to treat an eczema to great degrees. Also, rosemary oil has antibiotic and disinfectant properties that help with acne and treating oily skin conditions.
Rosemary oil is known for treating hair loss and baldness. The shrub oil increases blood circulation to hair follicles and reduces the risk of hair loss.
Are there any side effects of rosemary?
Everything in excess is damaging either to mental or physical functioning of the human body. When the rosemary is ingested in high quantities it leads to stomach problems, vomiting, seizures, and can even lead to kidney failure in larger quantities. So, make sure to only consume limited amounts of rosemary to avoid causing any side effects.
Thank you for reading this post on rosemary turning black. If you would like to learn more about rosemary growing and care, see this page.