You don't need an herb garden to grow rosemary. A single plant in a pot will provide you with enough rosemary to flavor your cooking and scent the kitchen. However, if you live in an area where rosemary thrives, you could have entire hedges of the plant.
Rosemary is one of those wonderful herbs that makes a beautiful ornamental plant as well as a versatile culinary seasoning. Its Latin name, Rosmarinus officinalis, means "dew of the sea," and rosemary is most closely associated with the cooking of the Mediterranean region.
- Botanical Name: Rosmarinus officinalis
- Common Name: Rosemary
- Plant Type: Herb; perennial evergreen shrub
- Mature Size: 3 to 5 feet tall and wide
- Sun Exposure: Full sun
- Soil Type: Sandy
- Soil pH: 5.0 to 8.0
- Bloom Time: January to April (when grown as perennial); late spring, summer (when grown in containers)
- Flower Color: Blue, white and pink
- Hardiness Zones: 9, 10, 11 (for perennial growth); 1, 2, 3, 4, 5, 6, 7, 8 (as annual or indoors)
- Native Area: Mediterranean
How to Grow Rosemary Plants
The three fundamentals for successfully growing rosemary are sun, good drainage, and good air circulation. If you live in a frost-free area, you can grow rosemary in the ground year-round, where it will grow into a lush, bushy shrub. In cold-winter climates, you can grow rosemary in the ground as an annual, or keep it in a container that you bring indoors well before the first frost.
To keep rosemary happy, give it 6 to 8 hours of full sunlight each day. When growing it indoors, place it in a south-facing window for bright light, but don't let it get too hot.
Grow rosemary in sandy, well-draining soil. This plant is native to the rocky hillsides of the Mediterranean and doesn't do well if its roots stay wet.
Water rosemary plants when the soil is completely dry. Be careful not to over-water and keep the soil wet (especially when growing in containers), as this leads to root rot.
Temperature and Humidity
Outdoors, rosemary can tolerate high temperatures and a wide range of humidity. Most varieties are hardy only to 30 degrees F. Where temperatures dip below 30 F, rosemary plants will have to spend the winter indoors. In this case, it's easier to grow your rosemary in a container all year. Since rosemary likes it on the dry side, terra cotta pots are an especially good choice. Just be sure the plants don't bake and completely dry out while outdoors during the summer.
Rosemary is not a heavy feeder, but fertilizing in spring with a fish/kelp emulsion will get it off to a good start for the season. Periodic foliar sprays with the emulsion will keep it looking great.
You will make things far easier on yourself if you start with a nursery-grown plant. Rosemary can take years to fill in, so expect to pay more for a mature plant than for a small rosemary start.
If you would like to start your own rosemary plant, the best option is to start with a cutting. Rosemary seed can be difficult to germinate and often do not grow true to their parent. It's much faster to start with a cutting, and you will be sure of what type of plant you will get.
To propagate with cuttings, snip about a 2-inch cutting from the soft, new growth of an established plant. Remove the leaves from the bottom inch, then dip the cut tip into a rooting hormone and place the dipped end into a container of dampened, sterile seed starting mix that drains well.
Place the container in a warm spot with indirect sunlight. Mist the cuttings daily and make sure the soil does not dry out. In about 2 to 3 weeks, test for root growth by very gently tugging on the cuttings. Once the cuttings have roots, transplant them into individual pots about 3 to 4 inches in diameter. Pinch off the very top of the cutting to encourage it to develop branches.
Potting and Repotting
If you're growing rosemary in containers, move your pots back outdoors once all danger of frost has passed. As with most potted plants, the soil in your rosemary pot will degenerate through watering and root growth. Re-pot at least once a year. Spring is the best time to re-pot your rosemary, but it should be fine no matter what time of year you get to it.
When the rosemary plant puts out considerable growth or looks like it just can't get enough water, it has outgrown its pot and needs to be transplanted into a larger one. If you want to maintain the size of your rosemary plant, root prune it by slicing off a couple of inches of the roots from the bottom and sides of the root ball and replanting in the same pot. Be sure to trim some of the top at the same time to lessen the workload of the roots and the stress placed upon the trimmed plant.
If you're growing rosemary for cooking, consider "Miss Jessup," "Tuscan Blue," or "Spice Island," all of which are all excellent choices for cooks. These are large plants that grow up to 4 to 6 feet tall when grown in the ground. They have large leaves that are very fragrant and hold their flavor when cooked or dried.
If you're growing rosemary in pots, "Blue Boy" is a small bush rosemary with proportionally small leaves that grow in clusters. "Golden Rain" is another variety that stays compact and small. Its new foliage has a weeping habit and light yellow markings that darken to green.
Common Pests and Diseases
The biggest problem with growing rosemary indoors is getting the humidity level right. High humidity and poor air circulation commonly result in powdery mildew on rosemary plants. Powdery mildew is a white, powdery fungus that can develop if the surrounding air is humid and there is not enough air movement. On the other hand, too little humidity will desiccate the leaves and quickly kill the plant.
Powdery mildew won't kill your rosemary outright, but it will weaken the plant. Try to balance the humidity by misting the leaves regularly but allowing the soil to dry somewhat between watering. In addition, keep the plant in sunlight and, if necessary, run a fan for a few hours a day to create a breeze.
Also be on the lookout for aphids and spider mites. These pests seem to live on houseplants for the winter. Catching them before a total infestation will make them easier to control. Repeated spraying with insecticidal soap, per package directions, should take care of the problem.