Rosemary tolerates most soil types, but does need excellent drainage. Lavandula angustifolia and x intermedia grows in well-drained, neutral-to-alkaline sandy or stony soils, while L. stoechas prefer more acid conditions.
Although many rosemary are frost hardy they need a sunny position protected from cold wind. Lavender, particularly the hardy varieties, withstand more exposed sites and can be used as protective foil when grown together. Half hardy and tender species are more suited to container growing unless in U.S. Department of Agriculture plant hardiness area zones 6 and 7.
Erect shrubby forms of Rosmarinus officinalis and cultivars like Miss Jessop's Upright can grow to 6 feet if unpruned, while shorter cultivars, like R. o. albiflora and R. o. Benenden Blue, only reach 32 inches. Prostrate or cascade types, such as R. lavendulaceus and R. o Severn Seas are more tender, early flowering and can spread from 3 to 6 feet if left to untrimmed.
Choose lavenders from the hundreds available in different heights, spread and color. L. angustifolia Blue Cushion, Lady Anne, Miss Muffett and nana alba are all small growers, reaching about 12 inches. Taller varieties at 18 to 24 inches include Hidcote, Arctic Snow, Beechwood, Munstead, Melissa Lilac, Royal Purple, and Coconut Ice. Lavendula x intermedia Grosso, Grappenhall, Grey Hedge, Seal and Fragrant Memories are taller, broader and later to flower than angustifolia with heights range from 24 to 36 inches.
Growing Side by Side
Plant a mixed hedge by alternating Lavandula x intermedia and Rosmarinus officinalis at a 3-foot spacing. This produces a medium-sized hedge of contrasting gray and green foliage with spring and summer flowering interest. Add color and fragrance to any garden by combining prostrate rosemary grown to the front of borders or over hanging a wall with lavender as a back drop. Alternatively, plant singly or in groups in south facing borders, paying attention to their spacing so that one does not overcrowd the other.
Extend longevity by keeping plants well-pruned to encourage new, healthy growth. Timing is dependant on plant hardiness and flowering season but in general, prune hardy lavenders after flowering and rosemary in spring or summer. Avoid pruning in late fall, as frost may penetrate their stems and damage or even kill the plants.