What is the Month to Plant Basil Outside?

Time Frame

• You can plant basil directly into the garden once the soil warms, or start it inside about six to eight weeks before the last frost date for your area. Frost-free dates vary by region and are determined by the United States Department of Agriculture which maintains listings of plant hardiness zones for all 50 states. The charts published by the USDA indicate the range of coldest and warmest annual temperatures, making it easier to determine frost dates for each region. What this translates to is that the last frost-free date for southern Oregon, for example, which falls in USDA zone 6, is vastly different from that of the southern tip of Florida, which is in zone 10. This means that gardeners can safely set out basil much earlier in Florida than in Oregon, and also that it can remain in the garden later in the season.

Examples

• Because basil cannot tolerate any amount of cold, it is only safe to transplant outdoors once the soil temperature reaches at least 60 degrees Fahrenheit, with the ideal around 70 degrees Fahrenheit. Only a few areas, such as Phoenix, Arizona, Miami, Florida, and parts of California, do not see regular frosts each year. The growing seasons in those zones exceed 330 days, making it safe to plant basil outdoors any time during the year. Elsewhere, it is safe to move plants outside any time after January 19 in Tucson, Arizona, for example; March 16 in Pine Bluff, Arkansas; April 30 in Denver, Colorado; May 2 in Portland, Maine; May 14 in Bismarck, North Dakota; and May 22 in Casper, Wyoming.

Variations

• With such wide variations between zones, another way to know when it's time to plant basil safely outside in your area is to note when seedlings appear in nurseries and garden centers. Even within a safe frost-free range, variations can occur based on micro-climates, which are conditions that exist in some areas close to others that do not. Topography has a lot to do with why it gets slightly colder in some areas within the same zone as others, as do the presence of dense vegetation and weather patterns. While time frames can vary slightly between these areas, the safe choice is to add a few days to the last frost-free date. Taking the soil's temperature and noting the results for several days is also sometimes more accurate than depending on calendar dates.

Hardening Off

• Moving basil seedlings from their cozy indoor environment to the harsher conditions outside is a shock to their systems. You can ease the transition by hardening them off, which means introducing them gradually to the outdoors. When the seedlings are about 6 inches tall, move them outside to a partially shaded area protected from wind. Keep the soil moist but not saturated, and bring them back inside if bad weather threatens or at dusk. If you do this every day for about a week, the basil seedlings will ease into their new homes in the garden with no ill effects once the soil is warm enough to receive them.