The most immediate and obvious difference lies in their fundamental growth pattern. Upright rosemary (Rosmarinus officinalis, often labeled as 'Tuscan Blue' or 'Arp') exhibits a strongly vertical, shrub-like habit. Its stems grow predominantly upwards, creating a dense, bushy plant that can reach several feet in height and width, resembling a small, aromatic shrub. In contrast, trailing (or prostrate) rosemary (Rosmarinus officinalis 'Prostratus') features long, pliable stems that grow outward and downward. It rarely achieves significant height but will spread vigorously across the ground or cascade elegantly over walls and containers, behaving more like a ground cover or a vine.
While the leaves of both types are the classic, needle-like, aromatic form synonymous with rosemary, subtle differences exist. Upright varieties tend to have slightly sturdier, more woody stems that support their vertical growth. The foliage is often a deep, dark green and can be very dense. Trailing varieties possess more flexible, less woody stems that are adapted for spreading and hanging. The leaves can sometimes be a lighter, brighter green and are often slightly broader, though this varies by cultivar. The essential oils that give rosemary its signature scent are present in both, though the concentration can vary more by specific cultivar and growing conditions than by the upright/trailing categorization alone.
Both varieties produce the characteristic small, two-lipped flowers that are highly attractive to bees and other pollinators. However, the visual effect of the bloom differs due to the growth habit. On an upright rosemary, the flowers appear clustered along the erect stems, creating bold splashes of color (typically blue or violet, sometimes white or pink) throughout the shrub. On a trailing rosemary, the flowers often form along the entire length of its cascading stems, creating a spectacular waterfall-like effect of color when in full bloom. This makes the trailing varieties particularly prized for ornamental use in hanging baskets and on retaining walls.
The root systems of these plants have adapted to support their distinct growth forms. Upright rosemary develops a robust, central root system that anchors its substantial above-ground structure and seeks deeper water sources. This can make it slightly more drought-tolerant once established. Trailing rosemary often develops a more fibrous and widespread, though sometimes shallower, root system. This network is excellent for stabilizing soil on slopes (erosion control) but may require more consistent moisture than its upright counterpart, especially when grown in containers where soil dries out quickly.
From a functional perspective, a gardener selects a variety based on its intended role in the landscape. Upright rosemary is typically cultivated as a standalone herb garden specimen, a low hedge, or part of a mixed shrub border. Its form is ideal for harvesting larger quantities of stems for culinary use. Trailing rosemary is primarily selected as an ornamental ground cover for sunny, well-drained slopes, for spilling over the edges of raised beds and stone walls, or for growing in hanging containers. Its culinary use is identical, but harvesting may be less convenient on stems that are lying on the ground.
