Successful herb gardening from seed depends on precise timing, which allows the young plants to mature under optimal conditions. While purchasing starter plants offers convenience, starting herbs from seed provides access to a greater variety of cultivars and is often more cost-effective. The planting schedule must be anchored to a specific environmental marker unique to your area, not just a calendar date. This planning ensures that fragile seedlings are not exposed to damaging cold and that slow-growing varieties have enough time to reach maturity before the end of the season.
Determining Your Local Timing Anchor
The single most important factor for timing any spring planting is the average Last Frost Date for your specific location. This date represents the average day in spring when the nightly low temperature is no longer expected to reach 32°F (0°C). Since this date is an average, it is based on historical climate data and carries a small probability of a later frost occurring.
Gardeners can easily determine their local date by using resources like the National Oceanic and Atmospheric Administration (NOAA) data or various online calculators. University extension services also provide this information. Establishing this date is foundational because every subsequent planting decision, both indoors and outdoors, is calculated by counting backward or forward from this environmental marker. It dictates the start of the safe growing season for frost-sensitive plants.
Indoor Starting Schedules for Tender Herbs
Starting seeds indoors is a technique used primarily for herbs that require a long growing period or are highly sensitive to cold temperatures. This process gives tender herbs a significant head start, allowing them to be transplanted as robust seedlings once the weather stabilizes. The timing for this activity is calculated by counting backward from your average Last Frost Date.
Many common perennial and slow-growing annual herbs, such as rosemary, oregano, thyme, and sage, benefit from an indoor start six to eight weeks before the last expected frost. Rosemary, in particular, is extremely slow to germinate and grow, often requiring a 10 to 12-week lead time to develop into a transplantable size. Providing this early, controlled environment ensures the plants reach their full productive potential during the outdoor growing season.
These young seedlings require specific conditions to thrive during their indoor phase, especially bright light for 14 to 16 hours a day to prevent them from becoming thin and weak. Basil, a highly popular but cold-sensitive annual herb, is often started indoors about four to six weeks before the last frost. Starting basil too early can result in leggy, overgrown plants that struggle to adapt to the outdoor environment.
Direct Sowing Timing for Outdoors
Direct sowing involves planting seeds directly into the garden soil and is suitable for two main categories of herbs: hardy, cool-season varieties and warm-season herbs that dislike transplanting. The timing for direct sowing is determined by the herb’s tolerance for cold and the required soil temperature for germination.
Hardy herbs, which can tolerate a light frost, are the first to be sown in the spring, often several weeks before the last frost date. These cool-season annuals and biennials, including cilantro, dill, and parsley, thrive in cooler soil temperatures, sometimes as low as 45°F (7°C). Dill can often be sown two weeks before the last frost, allowing it to germinate and establish itself before the summer heat causes it to bolt prematurely.
Conversely, tender, warm-season herbs must be sown only after all danger of frost has passed and the soil has warmed considerably. Basil and marjoram seeds, for example, will not germinate efficiently in cold soil and are susceptible to fungal diseases if planted too early. The soil temperature must typically reach a minimum of 60°F (15°C) for successful germination and healthy growth of these heat-loving varieties. Waiting for warm soil is also advisable for herbs like fennel, which transplant poorly, making direct sowing the preferred method.