Thyme plants are woody perennials, compact and evergreen or semi-evergreen. Upright, small shrub, low-growing, mounded, mat and creeping forms are available. The plants produce small flowers, but several flower color options are available among the varieties and cultivars. While some 400 varieties of thyme exist, not all are available locally, and only a precious few are suited for culinary use.
The species Thymus vulgaris is often referred to as common thyme and includes summer, winter and French thymes. Thymol is the active ingredient and component of the essential oil that gives the herb its flavor. Neral and geranial give lemon thyme (T. x citriodorus) its citrus aroma. Lemon thyme cultivars include Silver King, Silver Queen, Doone Valley and Argenteus. Cultivars are available that evoke other citrus aromas, such as lime and orange. Cold-tolerant species include oregano-scented thyme (T. pulegioides), which gets its flavor from carvacrol; and caraway thyme (T. herba-barona), which receives its essence from carvone. The names “creeping thyme” and “mother-of-thyme” are often used interchangeably for the same plants.
Culinary thyme varieties with the best flavor are narrow-leaf French, broadleaf English, lemon thyme and mother-of-thyme, recommends Master Gardener Joyce Schillen of the Oregon State University Extension Service’s Jackson County office. The plants have the best flavor just before their flowers open.
Use culinary thyme fresh or dried, as a garnish and to flavor vinegars, herbed butters, teas, meat dishes, salads and soups. Thyme is one of the ingredients in the herbes de Provence blend used in classical French cooking.
Culinary thyme may also serve as an ornamental. The plants attract bees and butterflies, the foliage offers an attractive scent and appearance, and variegated cultivars are available. For cooking, keep your plants close at hand. Thyme grows well indoors in a south-facing window and outdoors in gardens, borders, hanging baskets and containers. Some thyme plants make good groundcovers, and you can walk on creeping thyme, but you may not want to use plants grown in a pathway for cooking.
Thyme is a Mediterranean herb that prefers hot, dry conditions, but can survive in areas with mild winters. Thyme grows throughout all of the Sunset Climate Zones of San Francisco and its surrounding counties. The plants adapt well to the low average rainfall and variable conditions of the many microclimates of the region; however, plants grown in coastal or foggy areas may experience fungal issues. If your location experiences an occasional hard freeze, temporarily cover the herbs using a cloth, plastic sheet or mulch to prevent damage to the plants.
Soil and Fertilizer
Thyme tolerates poor soils. While chalky soils are best, sandy soils and rocky soils are also good for the plants. Thyme will have trouble on clay soils because of its shallow roots and need for good drainage. Amend the soil to provide a pH range of approximately 6.3 to 6.8.
Thyme benefits from a light fertilizer application once or twice yearly. Use an all-purpose or half-strength water-soluble fertilizer. If you apply nitrogen, use only one-fourth to half the recommended dose for vegetables in your area, suggests the Virginia Cooperative Extension. Using too much nitrogen may cause rapid growth and poor flavor.
Pruning and Harvest
Pruning is an important part of caring for thyme. It encourages new growth; and with culinary thyme, you can reap the rewards of the chore by eating what you remove. Prune thyme as needed throughout the year for immediate use by cutting the stems in the early morning after the dew dries. The flowering portions of the stems close to the tips contain more essential oil-producing glands and offer better flavor.
Prune thyme for propagation; you can start plants from stem cuttings, through division or seed. Prune to shape plants, reduce legginess and encourage air circulation. It’s safe to prune most thymes harshly, even by one-third to one-half, one or two times per season, but stop making significant cuts once late summer arrives if you live in a colder microclimate. In areas such as Sunset’s Climate Zone 7, the plants need time to recover before cold temperatures set in. Creeping thyme is more resilient, but with lemon thyme and thymes with mounding forms, leave at least a fifth of the plant unpruned, recommends the University of California Cooperative Extension, which suggests you trim these plants in a manner similar to a Mohawk haircut.