The genus Salvia, commonly known as sage, encompasses over 900 diverse species, ranging from tender annuals and short-lived perennials to hardy herbaceous plants and woody shrubs. The growth pattern depends entirely on the specific species or cultivar planted in the garden. Understanding how a salvia expands is the first step in successfully managing it within a landscape setting. This knowledge is essential for successful landscape planning.
Categorizing Salvia Growth Habits
Salvia species are categorized into two primary growth patterns: those that clump and those that run. Clumping varieties expand slowly from a single central crown, maintaining a contained footprint in the garden. They increase their size gradually as the plant matures but remain relatively compact.
An example of this habit is Salvia nemorosa, or Woodland Sage, a herbaceous perennial that forms a tight, upright mound. Cultivars like ‘Caradonna’ or ‘May Night’ spread only 12 to 24 inches wide from the original planting site. This growth pattern makes them well-suited for borders and mixed plantings where spatial boundaries are necessary.
Running salvias actively expand their territory by sending out specialized underground stems. These plants can be significantly more aggressive, sometimes spreading several feet in a single season under ideal conditions. The expansion is designed to claim new soil resources and establish new, separate plants away from the parent crown.
This habit is observed in certain native sages and specific cultivars that can quickly overrun a planting bed if left unchecked. A gardener must determine the specific growth habit of a species before planting it to avoid unwelcome colonization.
Specific Propagation Methods
Horizontal expansion occurs through specialized stems known as rhizomes or stolons, allowing the plant to reproduce asexually. Rhizomes are modified stems that grow horizontally underground, periodically sending up new shoots that emerge as individual plants. Stolons function similarly but are above-ground runners that creep along the soil surface and root at the nodes to form new plants. This asexual reproduction results in genetically identical clones, and the spread can be rapid, particularly in loose, rich soil with consistent moisture.
The sexual propagation method for many salvias is self-seeding. Species like Salvia coccinea, or Scarlet Sage, drop numerous viable seeds that germinate readily in disturbed soil. The seeds are often small and dispersed by wind, water, or small animals, scattering new seedlings outside the original planting area. Some salvia seeds require light for germination, meaning they sprout easily in bare patches of soil, resulting in hundreds of tiny new plants appearing the following season.
A third method, occurring mainly in shrubby types like Salvia microphylla, is layering, where a low-hanging branch touches the soil and develops roots, forming a new plant.
Strategies for Controlling Spread
For running varieties that utilize rhizomes, the most effective control is introducing a physical barrier into the soil. Planting these species within a bottomless container sunk into the ground can contain the underground stems. This prevents the plant from colonizing the adjacent garden space.
To control species that spread primarily through self-seeding, consistent deadheading is necessary. Removing the spent flower spikes before the seeds mature and drop drastically reduces the number of spontaneous seedlings the following year. This practice also redirects the plant’s energy toward producing new flowers, extending the bloom period.
For clumping salvias that increase in size over time, division is the solution. While these plants are not invasive, they can become less vigorous and flower less profusely after several years. Herbaceous clumping salvias, such as Salvia nemorosa, benefit from being dug up and separated into smaller sections every three to five years, which rejuvenates the plant and manages its overall size.