By Julie Christensen
Like most herbs that are native to the Mediterranean, rosemary (Rosemary officinalis) thrives in poor, rocky, alkaline soil and hot conditions. It’s winter hardy only in U.S. Department of Agriculture plant hardiness zones 6 through 10; elsewhere, it’s grown as an annual, or overwintered indoors. Even in zone 6 and 7, it usually needs some winter protection. Otherwise, this plant is as rugged and low-maintenance as they come.
Rosemary comes in many forms and there’s sure to be one that suits your garden. Creeping rosemary looks beautiful along a rock wall or climbing out of pots. Upright forms can be used to make an evergreen hedge in warm climates, where they eventually reach 5 to 8 feet tall. In most climates, rosemary stays under 3 feet tall, but looks lovely when combined with other perennials or used as a specimen plant.
Rosemary’s flowers, which bloom in fall to winter, depending on your climate, are generally blue. The shade of blue ranges, depending on cultivar, from vivid blue to pale blue. The needle-like leaves are an attractive silver to bluish-gray, which complements most landscaping schemes.
Planting Rosemary Outdoors
If you’re planting rosemary outdoors, select a spot that gets at least six to eight hours of sunlight daily. The soil should be well-draining, but not too rich. Rosemary prefers soil with a pH between 6.5 and 8.0. Add lime, if necessary, to raise the soil pH. Although you can start rosemary from seed, it grows very slowly. Most gardeners prefer to grow rosemary from cuttings or nursery transplants.
Make a hole as deep as the transplant and twice as wide. Slip the plant into the hole and firm the soil around it. Keep the soil slightly moist during the first growing season. Once established, rosemary rarely needs watering, except during very hot and dry conditions.
If you live in zone 6 or 7, plant rosemary in a sheltered spot, such as next to a south-facing wall or among other shrubs. In most cases, you won’t need to fertilize rosemary. Too much fertilizer – and water—is one of the leading causes of plant decline. Excess fertilizer and water causes the plant to produce brittle, woody branches with few leaves. These branches are more prone to winter damage.
To harvest rosemary, pinch off 5 to 6 inch stems from the branches. You can use the leaves fresh or hang the branches and allow them to dry. Once dry, strip the leaves from the stem and store them in a cool, dry location. Prune the plant back slightly after it has flowered. Since flowering occurs on the current season’s growth, if you prune earlier, you’ll remove the blooms.
Planting Rosemary in a Pot
If you have limited growing space or live in an area with cold winters, you can still grow rosemary in pots. Choose a pot that holds at least 1 to 2 gallons of soil. Use a sandy potting mix that is free of peat moss, since peat moss is acidic. Water rosemary planted in pots more frequently since water drains out quickly. Water just enough to keep the soil slightly moist to the touch. You may also need to fertilize potted rosemary occasionally if growth seems very slow. Fertilize once or twice per year with a dilute 10-10-10 fertilizer solution.
Be sure to bring the plant indoors before the first hard frost. Store it in a location that gets bright sunlight, such as a room with southern or western exposure. Over the winter, growth will slow and the plant will enter dormancy. Keep it in a cool room with temperatures between 55 and 65 degrees F. Mist the plant occasionally to increase humidity.
Pests and Problems
The main challenges with growing rosemary stem from improper growing conditions. The plants are prone to root rot in soggy soils, but this can easily be prevented by providing good drainage. Space rosemary plants at least 3 feet apart so air circulates freely since crowded conditions make rosemary prone to fungal diseases. Avoid overfertilizing and overwatering, as well.
Houseplants are sometimes afflicted by spider mites, aphids and whiteflies. Shoot the leaves with a steady stream of water, which usually takes care of these pests. If the problem persists, spray the leaves with an insecticidal oil or soap. Wait until new growth emerges to harvest and eat the leaves.
Varieties to Try
- ‘Tuscan Blue,’ is an upright shrub that reaches 5 to 7 feet tall. Its leaves are wider than most rosemary varieties and they’re an attractive blue-green color. Very rugged plant in warm climates.
- ‘Blue Spires’ is another upright shrub that reaches 4 to 5 feet. It makes a beautiful accent in a formal garden.
- ‘Collingwood Ingram’ grows 3 feet tall, with a rounded, bushy form.
- ‘Prostratus’ has a climbing form, growing 2 feet tall and up to 8 feet wide. Beautiful trailing down rock walls.
- ‘Arp’ tolerates temperatures to -10 degrees F., making it one of the most cold-hardy varieties.
All rosemary varieties can be used in cooking, but the upright types have the most oils. ‘Tuscan Blue’ and ‘Blue Spires’ are among the best culinary rosemary types.
Want to learn more about growing rosemary?
Visit the following websites:
Growing Rosemary from the Arizona Cooperative Extension
Rosemary from the University of Illinois Extension
P Allen Smith teaches about growing rosemary herbs on YouTube.
Learn how to propagate / grow rosemary from cuttings on YouTube.
Julie Christensen learned about gardening on her grandfather’s farm and mother’s vegetable garden in southern Idaho. Today, she lives and gardens on the high plains of Colorado. When she’s not digging in the dirt, Julie writes about food, education, parenting and gardening.