Rosemary is a woody perennial herb valued for its fragrant foliage and durability. Whether it spreads depends entirely on the specific variety planted, as its growth habit determines its lateral reach. While all varieties grow larger over time, the manner of this growth—focusing on height or width—dictates how aggressively the plant will appear to spread. Controlling this growth is largely a matter of initial selection and consistent maintenance.
Upright vs. Prostrate Growth Habits
The genus Salvia rosmarinus includes cultivars that fall into two main categories of growth. Upright, or shrub-like, varieties focus on vertical growth, forming dense, mounding shrubs that can function like small hedges. A common example, ‘Tuscan Blue’, can reach heights of 4 to 6 feet, with a spread typically contained to about half its height, making its lateral expansion slow and predictable.
Prostrate, or trailing, varieties exhibit a true spreading habit, behaving more like a ground cover. These cultivars feature long, pliable stems that grow outward and downward, making them excellent for cascading over walls or across slopes. Varieties like ‘Prostratus’ may only reach 1 to 2 feet in height but can spread vigorously, covering a diameter of 4 to 8 feet over time.
The growth habit also determines the root system. Upright forms develop a deeper central root structure to support their height. Trailing types tend to develop a widespread, fibrous root system ideal for stabilizing soil across a surface. Understanding this difference is the first step in managing potential spread.
Controlling Size and Shape Through Pruning
Pruning is the most effective way to manage the size and shape of any rosemary plant. The timing of this maintenance is important, with the best time to prune being in late spring or early summer, just after the plant has finished its main flowering period. This timing allows any new growth to harden off before the winter cold arrives.
Pruning should be done frequently and lightly, focusing on the green, leafy stems to encourage dense, bushy growth. Avoid cutting into the old, bare, woody sections of the plant, as rosemary does not readily regrow from this old wood. Making cuts just above a set of green leaves on the stem will stimulate new branching, which keeps the plant full.
For a plant that has become overgrown, a hard prune can be performed annually, removing about a quarter to a third of the plant. However, if the plant is neglected for too long and becomes entirely woody, it is often better to replace it with a new, younger plant rather than attempting a severe rejuvenation prune. Consistent, light trimming is the best strategy for long-term containment.
Ideal Conditions for Contained Growth
The growing environment influences the rate and aggressiveness of rosemary’s spread. Rosemary is native to the Mediterranean and thrives in full sun and well-draining soil. Planting in a location that receives six to eight hours of direct sunlight each day is beneficial for plant health.
The composition of the soil is a primary factor in managing growth. Rosemary prefers lean, sandy, or loamy soil and is highly susceptible to root rot in overly wet conditions. Excessive watering or planting in rich, heavily fertilized soil encourages rapid, lush growth that can become weak and prone to sprawling out of bounds.
Once established, rosemary plants in the ground require minimal supplemental water and generally do not need fertilizer. Allowing the soil to dry out completely between waterings helps keep the plant’s growth tighter and more contained. Providing these leaner conditions naturally slows the growth rate, resulting in a more compact and manageable shrub.