As an herb, basil takes a prominent place not just in your pantry but also in the medicine cabinet, but as with all other plants you grow in the garden, basil can succumb to the elements or pests and diseases or just grow old and lose its vivid green colors.
Why are my basil stems turning brown? Basil stems can turn brown for a number of reasons including root rot, fungal infections, or natural maturity. As the herb reaches the end of its life, the stems turn brown and dry up. Sometimes this discoloration of the stems happens prematurely and requires your intervention to save the plant.
It’s important to be able to tell the difference between basil stems turning brown from natural causes and when it’s a disease that needs treatment to prevent its spread to other plants. Read more to find out why basil turns brown and what you can do about it.
Why Basil Stems Turn Brown – 4 Possible Causes
Healthy basil stems often have a light green color, but when they start to turn brown, especially in the middle of the season, you need to inspect the plants closely to figure out what’s behind this symptom. In many cases, brown basil stems are a serious sign that something is wrong with the plants.
Natural Maturing of Plant
Like every annual plant, basil has one mission in life. It will try to flower and produce seeds before the end of the season. Once the plant blossoms and the flowers pollinate, the stems will turn brown and become woody.
This is part of the herb’s life cycle, and it doesn’t signify a pathogen or a disease. There’s nothing for you to do here but wait for the seeds to mature and harvest them for the next season.
Root rot is a common problem with many plants. This infection is hard to detect since it attacks the roots. By the time you notice the symptoms, most of the root ball will be gone. In basil, one of the first signs is the stem turning brown.
It’s the plant’s defense mechanism for self-preservation as it tries to conserve the little resources coming to it from whatever roots are still intact.
Most fungal infections specific to basil, including Fusarium oxysporum, are caused by high humidity levels, poor airflow, and wet soil. Fungal spores need moisture to flourish, and while some fungi infect the leaves, others cause the basil stems to turn brown before their time. Indoor basil plants are more prone to fungal infections than outdoor plants.
Basil is a warm-season plant that thrives in full sun, and when the temperature dips below 50℉., the plant goes into survival mode. The stems turn brown and woody as a way to protect the plant against harsh conditions.
What To Do When Basil Stems Turn Brown
Unless your basil plants are reaching the end of their life cycle, brown stems should be a red flag. You need to find out what’s causing the symptom and take immediate action to remedy the situation.
Protect Basil From Cool Temperatures
If your spring and summer seasons are dotted with unpredictable cold spells, plant your basil in pots, and keep them indoors when the temperature outside dips below 50℉. Place a heat mat, like this one, under the pots if the cold weather continues.
Trim Off Flowers
Flowering in basil signals the end of the lush foliage stage as the plant focuses on producing seeds. If you don’t want seeds and still want to harvest juicy basil leaves, cut the blooms as soon as they appear. This will prevent the stems from turning brown and will keep lush foliage on the plant.
Get Rid of Plants That Show Signs of Rot or Fungus
If one or more of your basil plants have root rot or other fungal infections, dispose of the infected plant immediately to prevent the spread of the disease to the rest of the plants. The safest way to dispose of infected plants is to burn them.
Basil Life Cycle
Basil goes through the following stages in its life.
- Germination: The seeds of basil often germinate between 7 and 10 days after planting. Start the seeds indoors 4 to 6 weeks before the threat of the last frost.
- Foliage: The plant will reach its maximum height of 12 inches tall and focus on growing stems and leaves. The stems are light green, and the leaves are vivid green.
- Flowering: The plant redirects its resources to produce as many flowers as it can at the cost of leaves. When the flowers begin appearing, the stems will turn brown and no new leaves will emerge.
- Seeds: Once the flowers are pollinated, they will fade as seeds develop inside each wilting flower. Once the seeds mature, the stems will turn woody and the plant reaches the end of its life cycle.
Why Is My Basil Turning Black?
If your basil is covered with black spots, it could be a sign of poor nutrients in the soil, fungal infection, or exposure to frost. Pests can also transmit bacterial infections that cause black spots on the stems and leaves of the herb.
Bring the basil inside to protect it against the cold weather at night, and feed it with plant food supplements. Treat pests with neem oil. Infected plants should be disposed of properly.
Why Is My Basil Bitter?
Irregular watering can cause the basil leaves to turn bitter. This covers both overwatering and underwatering. Water the basil regularly, and give it 1 inch of water a week during the growing season.
Another reason for bitter basil leaves could be the flowers. Once the plant blooms, the leaves become bitter. Cut the flowers as soon as they appear to encourage the plant to grow lush and juicy leaves.
Basil stems could turn brown due to root rot and other fungal infections or as a result of exposure to cold weather. The stems will naturally turn brown once the plant blooms.