One of the most popular Mediterranean herbs, rosemary is loved by many gardeners for its delightful culinary flavor and relaxing aroma. Rosemary (Rosmarinus officinalis L.) is the only species in the genus Rosmarinus and belongs to the Lamiaceae family. It is a perennial, needle-leaved shrub that is typically grown outdoors, as it can become quite large (up to 1 meter or more within a year) and woody. However, if you want to have a fresh herb supply year-round, you can propagate rosemary from stem cuttings or move small potted plants indoors for the winter. So, how to grow rosemary indoors?
Can Rosemary Be Grown Indoors?
Yes, rosemary can be grown indoors in pots, provided it receives special care and attention. This herb thrives with plenty of light and a precise watering regimen that keeps its loamy soil well-moisturized but not overly wet.
How to Grow Rosemary Indoors
Sunlight
Even when grown outdoors, rosemary prefers full sun (at least six hours per day) and tolerates shade only moderately. This can pose a challenge when growing rosemary indoors, as providing sufficient sunlight—especially during the short winter months—can be difficult. Ideally, potted rosemary should be placed on a bright windowsill that receives light throughout the day or in a well-lit room.
If you plan to bring a potted rosemary plant indoors after it has been outside all summer, gradually acclimate it by placing it in the shade for a few hours each day before moving it inside. This helps it adjust to lower light conditions.
Artificial Light
If providing six or more hours of direct sunlight daily is not possible, artificial lighting can be a good alternative. While no artificial light fully replicates natural sunlight, LED grow lights are a practical option. Since LED lights do not produce excessive heat, they can be placed close to the plants without the risk of burning them. If artificial light is the primary source of illumination for rosemary, the plant will need up to 14 hours of exposure per day.
Temperature and Humidity
Rosemary thrives in temperatures ranging from 12°C to 26°C. Even temperatures as low as 5-7°C typically do not harm the plant.
However, rosemary does not tolerate dry indoor air, which is common in many homes during winter. On the other hand, excessive humidity can also be problematic, leading to powdery mildew on the leaves. To maintain optimal humidity levels, place potted rosemary on trays filled with pebbles partially submerged in water. The evaporating moisture will help keep the air around the plant adequately humid.
Watering
Finding the right balance in watering rosemary can be tricky. When in doubt, it is better to underwater than overwater, as excessive moisture poses a greater threat than dryness. A good rule of thumb is to water when the top layer of soil feels dry but never let the soil completely dry out. Rosemary also absorbs moisture from the air, so gentle misting every ten days can help bridge the gap between waterings.
Air Circulation
Proper air circulation helps prevent powdery mildew and other fungal diseases. Good airflow is particularly beneficial in humid climates, but it is not as crucial in dry winter air.
Fertilization
For optimal growth, fertilize rosemary with a liquid fertilizer at the beginning of the growing season (spring) and continue monthly through fall. If you plan to use rosemary for cooking, opt for organic fertilizers or enrich the soil with compost.
Pruning and Maintenance
Frequent harvesting and pruning help keep rosemary bushy and healthy. When stems become large and woody, they can be cut and used as skewers for cooking.
Rotate potted plants daily to ensure all sides receive even exposure to light.
Choosing the Right Pot and Soil
Container Size and Drainage
To ensure proper drainage, select a pot with drainage holes at the base. Clay pots, which absorb moisture, can help maintain good drainage. The pot should be deep enough to accommodate the roots—30 cm is an ideal depth.
Soil and Drainage
Rosemary prefers dry, well-draining soil, similar to its Mediterranean origins. A sandy cactus potting mix is an excellent choice, but you can also mix sand into regular potting soil to improve drainage.
Planting and Repotting
Unlike many other herbs, rosemary can grow into a tall plant, reaching 1-1.2 meters. Not everyone has space for a massive rosemary plant indoors.
How can you keep your rosemary plant manageable? Repot it in spring into a pot of the same size. When repotting, trim the roots by about one-third to control its growth, then place the plant back into the same-sized container with fresh soil. If you want a larger plant, simply use a bigger pot and repot as usual.
Moving Rosemary Outdoors for the Summer
A potted rosemary plant can be moved outside to a sunny spot in the yard once nighttime temperatures consistently stay above 10°C. Like any indoor plant, it should be gradually acclimated to outdoor conditions by extending its time outdoors over one to two weeks. During this hardening-off period, bring the plant indoors at night.
When to Bring Rosemary Indoors
The arrival of frost signals that it’s time to bring your rosemary plant inside. If the plant has grown too large and unwieldy during the outdoor season, you can transplant it into a pot and trim it before moving it indoors. Alternatively, you can take stem cuttings and root them to create new plants that will grow throughout the winter.
How to Propagate Rosemary?
You can grow rosemary indoors, but it grows quite slowly when started from seeds, so the easiest way to propagate it is by taking stem cuttings. Cut and root them in a pot during the summer, then bring the pot indoors when temperatures start to drop.
How to Harvest and Prepare Rosemary?
Simply snip off small sprigs of rosemary, rinse them with cold water, and sprinkle them over your favorite dishes. The sprigs can also be used as a garnish. To make rosemary-infused oil, fill a container with olive oil, add rosemary sprigs, and heat over low temperature for 10 minutes, then strain the oil for storage.