Aromatic, fine-needled rosemary has fascinated people for thousands of years, from the legend that the Virgin Mary's cloak turned its flowers blue to Shakespeare's famous observation, "There's rosemary, that's for remembrance." Fortunately, gardeners don't need to remember many rules to keep this culinary and medicinal herb thriving, whether in the garden or by a south-facing window.
Whether you'll be growing rosemary in pots or in an herb garden, they'll need at least six hours of sun all day. Don't position the plants in low-lying areas prone to water runoff or swamping. Even potted plants are prone to root rot if settled into boggy areas.
Like other Mediterranean herbs, rosemary plants crave both sunlight and dry, rocky soil. If your garden beds tend toward clay or moist soil, add sand or fine gravel to the patch in which you'll be planting rosemary. (Also use this well-drained patch for rosemary's like-minded neighbors, including thyme, oregano, sage and lavender.) Raised beds or even slightly mounded beds improve drainage as well. Rosemary exudes more fragrance in alkaline than neutral or acid soils, according to the University of Florida. Check your soil's pH level by sending a sample to your local extension service or by buying a soil-testing kit. If the pH level registers as 7.0 or lower, add wood ash or garden lime to the soil to make it "sweeter," or more alkaline.
Lucky growers in Zone 7 or higher often use rosemary not just as a year-round herb, but as a shrubby landscape feature. Rosemary grows as much as 6 feet tall and wide in southern climates. Prune it regularly for more vigorous, non-scraggly growth. Alternatively, choose a creeping rosemary variety for ground covers, rock gardens and shallow containers. Its growing conditions are the same as those of upright rosemary plants.
For gardeners Zone 6 and lower, perennial rosemary is only a possibility if you bring the plants indoors for the winter. Either dig up the rosemary--the plants don't spread excessively, so finding the original root system is relatively easy--or keep the herbs in containers year round. Use terra cotta or lightweight plastic pots, keeping them on the patio or even sunken into the herb garden from summer through fall. Standard potting soil will provide the drainage these Mediterranean herbs crave.
In the winter, bring rosemary pots indoors and place them near a sunny window. The trickiest part about growing rosemary in pots, according to the University of Florida, stems from the herb's refusal to indicate when it needs watering. Although the plant dislikes consistently moist soil, it will perish from lack of water. Broad-leafed herbs tend to wilt or turn brown when under-watered, but rosemary needles don't indicate the distress the root system is under. The best watering method involves allowing a week or two to elapse between watering sessions, using potting soil for proper drainage, transplanting to larger pots as the rosemary grows and emptying the pot's saucer or drip tray if it fills with water.
To adjust rosemary to the decreased lighting even a sunny window will provide compared to that of an outdoor garden, get the potted rosemary used to less light while it is still growing outdoors. Move the pot into dappled sunlight for a week or two, then into deeper shade for another two to three weeks, before bringing it indoors. This practice lessens the shock to rosemary's system.