Creeping thyme (Thymus serpyllum) is a low-growing perennial herb valued primarily as a fragrant, dense ground cover. Unlike taller culinary relatives, this species forms a mat of tiny, semi-evergreen foliage that rarely exceeds four inches in height. It is an excellent choice for filling spaces between patio pavers, softening walkway edges, or providing erosion control on sunny slopes. Planting creeping thyme from seed allows for economical coverage of large areas, transforming bare ground into a green carpet that releases a pleasant scent when walked upon.
Preparing the Site and Seeds
Site selection is a primary factor in the successful establishment of creeping thyme, which thrives best in conditions mimicking its Mediterranean origins. The plant requires at least six hours of direct sunlight daily for robust growth and optimal flowering. Too little sun can result in sparse growth and reduced density of the ground cover mat.
The ideal soil must be lean and extremely well-draining to prevent root rot. Creeping thyme prefers a neutral to slightly alkaline pH, generally between 6.5 and 7.5. If your garden has heavy clay soil, amend the area by incorporating coarse materials such as horticultural sand, fine gravel, or grit to improve porosity. Work this preparation into the top few inches of the planting site to ensure water moves away quickly from the root zone.
Timing the sowing is important, with two main options available. For an early start, sow seeds indoors eight to ten weeks before the average last frost date. Direct sowing outdoors should be delayed until late spring or early summer, ensuring soil temperatures are consistently in the high 60s Fahrenheit or warmer, and all danger of frost has passed. While cold stratification is not strictly required, a brief period of cold, moist conditions can sometimes improve the germination rate.
Sowing Techniques for Creeping Thyme Seeds
The seeds of Thymus serpyllum are minuscule, requiring careful attention to depth during sowing. Since these seeds require light to germinate, they must not be buried beneath the soil surface. This is a physiological requirement for the seed to break dormancy.
Starting seeds indoors is generally recommended as it provides greater environmental control during the vulnerable germination phase. Use a sterile, fine-textured seed-starting mix in shallow trays or small cell packs. Gently press the seeds directly onto the surface of the moistened mix, ensuring firm contact without covering them with soil. A very light dusting of fine vermiculite can be applied to help retain surface moisture without blocking the necessary light.
Place the trays in a warm location, ideally maintaining a soil temperature between 65 and 75 degrees Fahrenheit, often achieved using a propagation mat. If direct sowing outdoors, rake the prepared soil surface to a fine tilth and broadcast the seeds thinly across the area. Lightly tamp the soil surface to press the seeds into the earth. Initial watering must be done gently, using a fine misting spray or bottom watering, to avoid washing the seeds away.
Care and Establishment of Seedlings
Creeping thyme is slow to germinate, often taking between 14 and 28 days to emerge. During this period, maintaining consistent moisture is paramount for success. The surface of the planting medium should never dry out completely, but it should also not remain saturated, which can encourage fungal issues like damping-off.
For indoor starts, seedlings need strong light immediately upon germination, best provided by a dedicated grow light system. Once the seedlings develop their first set of true leaves, they must be thinned to reduce competition. Thin the plants so remaining seedlings are spaced six to twelve inches apart, allowing room to spread into a dense mat.
Before transplanting indoor-started seedlings outdoors, they must undergo “hardening off.” This involves gradually acclimating the young plants to outdoor conditions, including direct sun, wind, and cooler temperatures, over seven to ten days. Once the threat of the last spring frost has passed, the hardened seedlings can be moved to the garden. After establishment (six to eight weeks), the plants become highly drought-tolerant and require minimal supplemental water or feeding.