When to plant Sweet Alyssum
Computed from land-grant Extension planting-window rules (cited below), localized to real ZIP-level median frost dates, not a single national guess. These are national-generic rules by hardiness class; individual state Extension offices layer their own regional adjustment on top (earlier in the Deep South, later in the Upper Midwest). Enter your ZIP for your own dates, or read the four representative locations below.
Planting windows and crop timing here are computed from USDA/NOAA climate data and the university extension sources cited below, not a site visit or soil test. Treat this as a starting point: local conditions vary, and a local nursery or extension office can advise on your exact site. See our full Disclaimer.
Representative timing, by climate band
When to plant Sweet Alyssum in four US climates
Each column is the most nursery-dense location in our directory within that USDA zone band, computed from that location's own real median frost dates, not a made-up example.
| Stage |
Zones 1-5 (cold winters)
Fort Plain, NY |
Zones 6-7 (temperate)
McMinnville, TN |
Zones 8-9 (warm)
Apopka, FL |
Zones 10-13 (hot, frost rare or absent)
Loxahatchee, FL |
|---|---|---|---|---|
| Start seed indoors | Mar 25–Apr 1 | Feb 24–Mar 3 | Jan 13–Jan 20 | – |
| Direct-sow outside | Mar 25–Apr 8 | Feb 24–Mar 10 | Jan 13–Jan 27 | – |
| Transplant outside | Apr 29–May 6 | Mar 31–Apr 7 | Feb 17–Feb 24 | – |
| Fall planting | Not available | Not available | Not available | – |
| Expected harvest | Jun 10–Jul 1 | May 12–Jun 2 | Mar 31–Apr 21 | – |
Zones 10-13 (hot, frost rare or absent) (Loxahatchee, FL): Frost is rare here (about 359 frost-free days a year); most years see little or no hard freeze. This is a hardy crop. In climates like this one, hardy and semi-hardy crops typically go in during the cooler months (fall through late winter), not on a frost-relative schedule.
Sweet alyssum splits between two readings of the same cold tolerance. University of Illinois Extension lists it among hardy annuals, about four weeks before the frost-free date, alongside pansy, snapdragon, and calendula, and NC State Extension's Plant Toolbox notes it can persist as a short-lived perennial, overwintering in USDA zones 5a through 9b, both pointing to real cold tolerance. Clemson Cooperative Extension's dedicated Sweet Alyssum factsheet instead calls it a cool-season annual with more half-hardy timing: direct-sow several weeks before the last frost, or start indoors five to six weeks before.
This page classifies sweet alyssum hardy and blends Illinois's specific "four weeks before" with Clemson's looser "several weeks" language into a six-to-four-week direct-sow window, publishing the range both sources allow rather than averaging them into one number neither printed. Indoor sowing and bloom time, five to six weeks to transplant and six to eight weeks (42 to 56 days) to first bloom, come directly from Clemson.
Where NC State's zone range applies, sweet alyssum can overwinter as a short-lived perennial rather than needing replanting each spring. Clemson also mentions a September fall-sowing option for winter bloom, but that date is specific to South Carolina and doesn't translate to a generic weeks-before-first-frost figure, so this page leaves that field blank.
Sweet alyssum is sold both as seed and as nursery flats.
Frost hardiness
Hardy. Tolerates hard frost. Can go in the ground before the last frost date.
Days to maturity
42–56
Sourcing notes
DISAGREEMENT: University of Illinois Extension lists sweet alyssum among hardy annuals (~4 weeks before frost-free date, with pansy, snapdragon, calendula, dusty miller), and NC State Extension Plant Toolbox notes it can persist as a short-lived perennial overwintering in zones 5a-9b -- both indicating strong cold tolerance. Clemson's dedicated Sweet Alyssum factsheet instead calls it a "cool-season annual" and gives more half-hardy-style timing: direct-sow "several weeks before the last frost date," or start indoors 5-6 weeks before, with a September fall-sowing option for winter bloom. Classified hardy here, blending Illinois's specific "4 weeks before" figure with Clemson's "several weeks" language into a -6 to -4 week direct-sow window; indoor-sow (5-6 weeks) and bloom time (6-8 weeks = 42-56 days from sowing) are both sourced directly from Clemson. The September fall-sow date is regional (South Carolina) and not translatable to a generic weeks-before-first-frost figure, so that field is left blank.
Related crops
Growing zones for this crop
Nurseries near these locations
Sources
- Clemson Cooperative Extension Home & Garden Information Center, Sweet Alyssum (accessed 2026-08-04)
- University of Illinois Extension, Annuals (Flowers) (accessed 2026-08-04)
- NC State Extension Gardener Plant Toolbox, Lobularia maritima (accessed 2026-08-04)