Rosemary (Rosmarinus officinalis) is an important culinary herb used to flavor chicken, pork, lamb and many other dishes. The plants are compact and grown as annuals in areas below USDA growing zone 7. In warmer areas, plants can be left in the ground year-round. Starting rosemary from seed can be tricky, as germination rates are usually poor and it takes several months before the plants produce any usable leaves. A combination of heat, light, moisture and the right type of planting medium are necessary to successfully grow this herb in the garden or in pots on a windowsill.
Select clean planting trays, wash thoroughly in a mild solution of soap and warm water and allow to air dry in order to create a sterile environment for seed germination.
Fill trays to 1 inch from the top with fresh sterile seed-starting medium and level. Water planting medium until it is wet but not saturated, to help settle it in the tray.
Place rosemary seeds on top of the planting medium about one-half inch apart and press lightly but do not cover with soil, as the seeds must only come into contact with soil but not buried in it.
Cover trays with clear plastic film, leaving one end loose to allow for air circulation. Place trays in a dark place with a temperature of 75 to 85 degrees Fahrenheit, as rosemary seeds need plenty of heat to germinate.
Check trays daily for moisture content and mist lightly if the soil appears dry, as this creates less seed disturbance than normal watering.
Move trays to a sunny location or place them under a grow light and remove the plastic film once seedlings emerge. Begin transplanting them when they are about 2 inches tall to individual pots or peat pots. Check frequently for moisture and water if the soil appears very dry.
Transplant rosemary when it is about 4 to 5 inches tall to larger individual pots or into the garden in a sunny location when the soil has warmed to at least 50 F. Lift bare-root seedlings gently out of the soil and place them in prepared holes in larger pots, or plant the entire peat pots in the soil up to the base of the plants. Allow the soil to dry between waterings, but provide additional water during extended dry spells.
Harvest rosemary sprigs when the plants are about 1 to 2 feet tall or about 70 to 90 days after germination. Mulch heavily in USDA plant hardiness zones 7 to 9 if leaving the plants outside for the winter, or gradually acclimate potted plants to changes in temperature if bringing potted plants inside in colder areas.
Things You Will Need
- Rosemary seeds
- Sterile seed-starting medium
- Starter trays
- Warm water and mild soap
- Clear plastic film
- Peat pots
- Large pots with a diameter of at least 12 inches
- Germination rates for rosemary are unreliable, so the more seeds you plant, the better your chances of producing a few good plants.
- To improve your chances of success, buy fresh new seed that has been dated for the current year and be sure the soil seedlings are transplanted into is rich, light and well aerated, and slightly alkaline. Perform a soil pH test before transplanting into the garden if you are unsure of your soil's acidity level.
- Rosemary needs at least 6 hours of direct sunlight per day for proper growth.
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