Rosemary Plant

The rosemary plant (Salvia rosmarinus) is a fragrant herb that grows as a perennial rounded evergreen shrub. It features slender, needle-like, gray-green leaves on erect woody stems. And it produces clusters of small, light blue to white flowers typically in the late spring to early summer, though it can bloom at other points of the year as well. Plant rosemary in the spring after any threat of frost has passed. You can grow rosemary indoors, too, though it will grow quite large. The shrub has a moderate growth rate and spreads when planted.

How to Plant Rosemary

When to Plant

Rosemary is best planted in the spring once the weather has warmed and there’s no frost in the forecast. Containers indoors generally can be started at any time of year.

Selecting a Planting Site

Rosemary grows best in a sunny spot that has soil with sharp drainage. Make sure no taller trees or shrubs in the area are so close that they will shade the rosemary. Rosemary also grows well in containers both outdoors and indoors, as long as it can get enough light.

Spacing, Depth, and Support

Space rosemary shrubs at least 2 to 3 feet apart. Plant seedlings and nursery plants at the same depth at which they were growing in their previous container. Seeds should be just barely covered with soil when planting. A support structure is typically not necessary for this shrub.

Rosemary Plant Care

Light

Rosemary likes full sun and does not tolerate shade. This means it requires at least six hours of direct sunlight on most days. A south-facing window is ideal for indoor growth, and grow lights are often necessary to provide supplemental light. Bring indoor plants outside in warm weather to allow them access to natural sunlight. Inadequate light can cause leggy and weak growth.

Soil

A well-draining sandy or loamy soil is best for rosemary. It doesn’t grow well in heavy clay and wet soils. A slightly acidic to neutral soil pH is ideal (6.0 to 7.0).

Water

Rosemary shrubs have good drought tolerance once they are mature, and it’s better to underwater rather than overwater them. Allow the top few inches of soil to dry out between waterings, and then water so that the soil is evenly moist but not soggy.

Temperature and Humidity

This shrub likes warm weather and moderate humidity levels. Most rosemary varieties can’t survive temperatures below 30 degrees, but they have good heat tolerance. They prefer temperatures between 55 degrees and 80 degrees. Moreover, high humidity can lead to rot and fungal issues, especially if there isn’t enough air circulation around the plant.

Fertilizer

Rosemary is not a heavy feeder. Mixing compost into the soil at the time of planting can help to give the shrub a healthy start. Then, using a balanced liquid fertilizer, following label instructions, will continue to promote quality growth.

Pollination

Rosemary shrubs self-pollinate and attract bees and other pollinators to the garden. Bring indoor plants outdoors in warm weather when their flowers are open to allow the blooms to naturally pollinate.

There are several types of rosemary to grow, including:

• ‘Arp’: This plant has light green foliage with a lemony scent, and it’s known for its cold tolerance.
• ‘Golden Rain’: This plant stays compact at 2 to 3 feet high and wide, and it features yellow markings on its foliage.
• ‘Albus’: The trademark of this cultivar is its white flowers.
• ‘Prostratus’: This cultivar has a low, spreading growth habit at around 2 feet high and 2 to 3 feet wide.

Rosemary vs. Lavender

Rosemary and lavender are similar in appearance. Both are shrublike with woody stems, and they feature aromatic leaves that are long and thin. However, rosemary plants generally grow larger than lavender. Rosemary blooms form among the foliage while lavender blooms rise above the foliage on flower spikes. And lavender has a lighter and more floral taste and aroma than rosemary.

Harvesting Rosemary

Rosemary can be harvested at almost any time of year, though spring and summer are when it grows most actively. And the leaves are most flavorful and aromatic just before the plant blooms. To harvest, use pruners to cut off 4- to 6-inch stem tips.

Use fresh rosemary sprigs or leaves in cooking as you like. Or hang the stems upside-down in a dry, cool, well-ventilated area for drying, which should take a couple of weeks. Once the stems are dry, strip off the leaves and keep them in an airtight container in a pantry.

How to Grow Rosemary in Pots

Growing rosemary in pots allows you to bring it indoors during cold weather. You also can keep containers on a patio or deck near your kitchen for easy access while cooking. Select a pot that’s slightly larger than the plant’s root ball. Make sure it has drainage holes. An unglazed clay container is best to allow excess soil moisture to evaporate through its walls.

Pruning

Prune rosemary as necessary to shape its growth after the plant is done flowering. Rosemary responds well to pruning and can be trained into topiary shapes. But don’t prune off more than a third of the plant at a time, as this can stress the shrub and leave it vulnerable to diseases and pests.

How to Grow Rosemary From Cuttings

If you would like to propagate your own rosemary plant, the best option is to start with a cutting. Not only is this an inexpensive way to get a new plant but taking cuttings from a mature plant can help to promote more branching and bushier growth. The best time to take a cutting is in the spring or summer. Here’s how:

1. Cut a piece of healthy stem that’s a few inches long. Choose new softwood growth for best results.
2. Remove the leaves on the lower portion of the stem, leaving at least five leaves.
3. Dip the cut end in rooting hormone.
4. Plant the cutting in a moist soilless potting mix in a small container that has drainage holes.
5. Place the container in a warm spot that has bright, indirect light. Mist the cutting daily, and make sure the growing medium doesn’t dry out.
6. In about two to three weeks, gently tug on the stem to check for roots. If you feel resistance, you’ll know roots have developed. After that, the cutting is ready for transplanting.

How to Grow Rosemary From Seed

Growing rosemary from seeds can be difficult because they don’t germinate easily and they often do not grow true to their parent plant. If you wish to try growing rosemary from seed, plant several more seeds than the number of plants you hope to grow. Start seeds around three months prior to your area’s projected last frost date in the spring. Take these steps:

1. Scatter the seeds in a tray filled with moist seed-starting mix, just lightly covering them with the mix.
2. Cover the tray with plastic wrap to trap moisture, and make sure the mix doesn’t dry out.
3. Place the tray on a heat mat to keep the soil between 80 degrees and 90 degrees Fahrenheit.
4. As soon as seedlings appear, remove the plastic wrap, and place the tray in bright light.
5. Once seedlings are around 3 inches high, move them to individual pots or outdoors if the weather is warm.

Potting and Repotting Rosemary

Use a light, well-draining potting mix when growing rosemary in a container. Plan to repot every year into one container size up, using fresh potting mix. The best time to repot is in the spring. Gently loosen the plant from its previous container, and situate it at the same depth in the new one, filling around it with soil.

Overwintering

Bring rosemary indoors well before any frost is predicted in the fall forecast. Keep it in a warm room and away from any drafts or drying air from heat vents. Continue providing it with at least six hours of sunlight per day via a bright window and/or grow light. And slightly back off on watering, though don’t allow the soil to fully dry out. Once frost is out of the forecast in the spring, the plant can go back outside.

Common Pests and Plant Diseases

High humidity and poor air circulation can result in powdery mildew—a white, powdery fungus—on rosemary plants. Powdery mildew typically won’t kill a plant, but the disease will weaken it. To prevent powdery mildew, make sure the plant’s soil isn’t too wet, and provide a few feet of space around it for airflow.

Also, be on the lookout for aphids and spider mites, especially on indoor plants. Use an insecticidal soap as soon as you spot an infestation to prevent it from spreading.