The USDA Hardiness Zone 6 designation indicates a region where the average lowest winter temperatures fall between -10°F and 0°F. For spring planting, this translates to an average last frost date typically ranging from April 1st to April 21st, though local microclimates can shift this window. February is a significant planting month because it is reserved for species that require a long lead time, often 10 to 12 weeks, before they can be safely transplanted outdoors after the frost risk has passed. Starting seeds in February allows gardeners in Zone 6 to cultivate plants with extended maturity periods, ensuring a harvest before the first fall frost arrives.
Long-Duration Vegetables for February Starting
Alliums, such as onions and leeks, are prime examples of slow-growing vegetables, requiring an 8- to 10-week head start to achieve the necessary size for bulbing or thickening once planted out. For successful germination, these seeds should be sown shallowly and kept in a cool location under bright grow lights for 16 hours daily. Onions and leeks are long-day plants in Zone 6, meaning they need increasing daylight hours to trigger the bulbing process, which makes the earliest possible start date beneficial.
Warm-weather nightshades, peppers and eggplants, must also be started in February to ensure they produce a harvest. These plants are slow to germinate and grow, requiring 8 to 10 weeks of indoor cultivation before transplanting. Pepper and eggplant seeds need high soil temperatures for successful germination, ideally between 75°F and 90°F, which is best achieved using a dedicated heat mat. Once germinated, the seedlings can be grown at slightly cooler air temperatures, but they should never be rushed outdoors, as they are highly sensitive to cold soil and air.
A few brassicas and root vegetables also benefit from a February start. Celery and its relative, celeriac, are among the slowest, often needing 10 to 12 weeks indoors before being ready for the garden. Certain slow-maturing cabbage varieties also fall into this early window, as they need to be large and established to withstand being set out a few weeks before the last frost date. These cool-season crops prefer cooler ambient temperatures once sprouted, thriving in a daytime environment around 65°F.
Ornamental Seeds to Begin Indoors
February is the time to begin ornamental plants that exhibit slow growth or a long germination period. Annual flowers such as petunias and snapdragons (antirrhinums) need this early start to ensure they are large enough to bloom early in the garden season. Petunias require approximately 10 to 12 weeks of indoor time before the average last frost date. Their seeds are tiny and require light for germination, so they should be surface-sown and kept consistently moist.
Other flowers that benefit from this early start include slow-germinating perennial varieties that are commonly grown as annuals in Zone 6, such as verbena or certain types of salvia. Starting these types now gives them time to establish a strong root system and foliage before the spring planting season arrives. Impatiens are another annual that should be started 8 to 10 weeks before the last frost, as they take longer to mature than many common bedding plants.
Avoid sowing seeds for fast-growing annuals like zinnias, marigolds, or cosmos during this February window. These species mature quickly and should be started much later, closer to 4 to 6 weeks before the last frost, or they will become root-bound and overly large before the weather is warm enough for outdoor planting. Focusing the February effort solely on long-duration varieties maximizes the utility of limited indoor growing space and light resources.
Calculating Timing and Hardening Off
Determining the precise last frost date is the foundation of successful seed starting, overriding the general Zone 6 range. Gardeners should consult local resources, such as university extension offices or online calculators, to find the average date. Once the anticipated last frost date is established, the sowing date is calculated by counting backward the recommended number of weeks for each specific plant variety. For example, a plant requiring 10 weeks of indoor growth should be sown 10 weeks before the target transplant date.
The process of hardening off is necessary for all seedlings started indoors, especially those sown in February. This procedure gradually acclimatizes tender indoor plants to outdoor conditions, including direct sunlight, wind, and fluctuating temperatures. Hardening off should begin 7 to 10 days before the scheduled transplant date.
Placing the seedlings in a sheltered spot, such as a porch or beneath a tree, for only a few hours on the first day is the start. The time spent outdoors must be incrementally increased each day, gradually introducing more direct sunlight and wind. This slow transition prevents transplant shock, which can stunt the growth or even kill seedlings that have only known the indoor environment.