Popular for its wonderful flavor and fragrance, rosemary is a valued herb in the culinary world and is used to season many dishes.
Grown indoors or outdoors, this gorgeous, evergreen perennial herb with its needle-like foliage also makes wonderful ornamental plants.
Native to Asia and the rocky hills around the Mediterranean Basin, rosemary (Rosmarinus officinalis) is an evergreen perennial shrub featuring needle-like leaves. Rosemary is commonly grown as an outdoor plant.
It can grow up to 3-4 feet tall and up to 4 feet in width and grow purple, blue, pink, or white flowers. In the US, the perennial grows in the USDA hardiness zones 8 to 10.
Commonly grown from cuttings, rosemary can also be grown from seeds, although it is quite difficult. In this article, we’ll discuss how to grow rosemary from seeds and when to start rosemary seeds indoors.
How to Grow Rosemary from Seeds Indoors
When to Start Rosemary Seeds Indoors
As mentioned earlier, rosemary is quite difficult to grow from seeds. This is because the seeds usually take a very long time to germinate, around 15 to 25 days, and the seedlings are quite slow to grow.
It is best to start the rosemary seeds indoors, by sowing them from late winter to early spring, around 10-12 weeks before the last frost in your area. The soil must be maintained at an optimal temperature of 80°F-90°F (27°C-32°C).
How to Start Rosemary Seeds Indoors
Prepare the Seed-Starting Mix
Choose a seed-starting tray and fill it with a soil-less potting mix. In nature, rosemary grows well in rocky and sandy soil and so the seeds will grow best in a light, loose, and well-draining potting mix.
It may be a good idea to create your own potting mix with peat moss, perlite, and bark or you can buy a sterile seed-starting mix without any soil from the garden store. Moisten the potting mix lightly before adding it to the seed-starting container.
Add the Seeds
Sprinkle around 3-4 seeds into each cell of the container on top of the seed-starting mix. Since the germination rate of rosemary is not very high, by planting multiple seeds in each of the cells, you can increase the success rate.
Place the seeds on top of the soil mix. Avoid pressing them into the soil.
Using a spray bottle, lightly mist the seeds with water. Ensure that the surface of the soil is moist but not wet and soggy. This will help the seeds to settle into the soil mix.
Cover with Some Potting Mix
Sprinkle a thin layer of potting mix on the entire surface, just sufficient to cover the rosemary seeds. But make sure not to put a lot of soil that prevents the seeds from getting sufficient sunlight.
Spritz some more water on the soil to dampen it. Make sure that the soil is just moist and not wet.
Cover the Seed Tray
Cover the seed tray with a plastic wrap or plastic dome. This will help to keep in the moisture, as well as warmth, helping the seeds to germinate more quickly.
Let the plastic wrap or dome remain on the tray until the seeds germinate and the seedlings appear.
Place the Tray in a Warm and Sunny Area
For germination, rosemary seeds require both sunlight and warmth and so it is important to place the tray in a sunny area that gets ample direct sunlight every day.
If you’re not able to find a warm and sunny location, then you can place the seed-starting tray on a heating mat and also use a full-spectrum indoor light to provide light and warmth for the seeds.
If the surface of the potting mix seems dry, then take off the plastic cover and mist with water lightly. Typically, the rosemary seeds can take up to 15-25 days to germinate.
Remove the Plastic Cover
Once the rosemary seeds germinate and the seedlings begin to appear, remove the plastic wrap/dome and then, place the seed-starting tray in a shallow tray filled with water.
The water will penetrate the soil via the drainage holes of the container. Then, place the seedlings in direct sunlight.
Plant the Seedlings in the Garden
Transplant the seedlings outdoors, when they are around 3-6 inches tall.
You can transplant the seedling into a garden bed or if you want to bring your plants indoors during the winter when the temperatures drop, then it may be a good idea to plant the seedlings in a pot.
Keep the rosemary plants in their pots for the first winter and protect them from the cold. You can transplant them outdoors when the weather turns warm.
When planting outdoors, plant them in well-draining soil, spacing them around 18-24 inches apart, and then gradually, reduce the watering.
Rosemary Plant Requirements
But before you transplant the seedlings outdoors, make sure to harden them off for at least a week in a sheltered place like a covered patio or porch. Rosemary does well in a well-draining compost-enriched slightly acidic soil with a pH level between 6.5 and 7.0.
Rosemary needs plenty of light for optimal growth. When planting the rosemary seedlings outdoors, choose a location, where the plants will get around 6-8 hours of direct sunlight every day.
If you’re growing your rosemary plants indoors, then place the container in a sunny window on the east or south side of your home, where the plant will receive ample sunlight.
If your area does not get sufficient sunlight, then it may be a good idea to use grow lights to give your plant the light it needs.
Rosemary plants need consistent temperature conditions to grow optimally. Any sudden temperature change can cause the plant to die.
Bring your rosemary plants indoors if there is going to be any sudden temperature change and if the plants are outdoors, use row covers to protect them.
In general, rosemary plants are frost tolerant; however, they don’t do too well in the case of extremes.
You can reduce any problems caused by temperature dips by planting the rosemary in a protected area near a brick wall or fence, which protects the plants from the wind and provides warmth.
The most important aspect to ensure that your rosemary plants grow healthily is adequate watering. Too little water or overwatering can kill the plants. Before watering your rosemary plant, test the soil with your finger.
If the soil is dry, then water it, but if it is moist, then let it dry before watering. In arid conditions, your rosemary plants may benefit by getting occasional misting of water.
Rosemary plants do well in organic-rich soil and do not need a lot when it comes to fertilizers. You can feed the plants liquid fertilizer once a month. To boost the health of the plant, add fish emulsions or worm castings annually to enrich the soil.
In conclusion, starting rosemary seeds indoors is rather difficult but not impossible. And, by using the information in this guide, you can successfully grow this amazing, fragrant herb easily at home.