Basil

When to plant basil, as 3 university extension services put it: conditions to wait for rather than calendar dates.

Family: Lamiaceae5
Type: Herb
Rules: 5
Last reviewed: 2026-11-02

Garden experts do not always agree, so I show every rule side by side.

When to plant basil

No source we hold times basil in weeks from a frost date, so this site gives no calendar dates for it. The sources describe conditions to wait for instead:

Transplant outdoors: Transplant well after the frost-free date, when soil is at least 60°F1 (Illinois)
Start indoors: Allow about 3-4 weeks indoors to produce transplants (counted from the transplant date, not a frost date)1 (Illinois)
Transplant outdoors: Transplant when daytime temperatures are consistently in the 70s °F and nights are above 50°F2 (Clemson)
Start indoors: Sow indoors 4-6 weeks ahead of the outdoor planting time (not tied to a frost date)2 (Clemson)
Sow outdoors: Sow seed outdoors after all danger of frost has passed4 (Maryland)

Growing facts

Table 3. Each value as one source states it. Sources measure differently, so values are not averaged.
Fact	Value	Source
Frost tolerance	tender	Illinois1
Minimum soil temperature	60°F	Illinois1
Days to germinate	5-7 days	Illinois1
Days to germinate	5-10 days	Clemson2
Days to maturity	30 days from transplant	Arizona (AZ1005)3
Days to maturity	60-75 days from seed	Arizona (AZ1005)3
Spacing	24 in in the row, rows 36 in apart	Clemson2
Spacing	12 in in the row, rows 18 in apart	Maryland4

Companions, and how sure anyone is

Tomatoes · Disputed Tested in a study
Claims: basil raises combined yield, improves tomato flavour and masks tomatoes from thrips and hornworms. Garden-scale trials found no consistent flavour effect and mixed yield results.6 6 6 7 7 8 8 9 10
Bomford 2004 thesis (not peer reviewed): basil companions gave a mean 20% relative-yield advantage, largest at high density and high basil share; no consistent taste preference. Bomford & Butler 2003 abstract: no LER significantly above 1; tomato pests did not respond. Penn State says basil masks tomatoes from thrips and hornworms but cites no study. Conboy 2019 (glasshouse): a marigold mix that included basil reduced whitefly; basil alone untested.

All basil companions, with sources · The full companion chart

Sources

University of Illinois Extension, Basil (Herb Gardening). Retrieved 2026-11-02.
Clemson Cooperative Extension, Home & Garden Information Center, Basil (HGIC 1327), Originally published 12/08; updated May 1, 2019. Retrieved 2026-11-02.
The University of Arizona Cooperative Extension, Vegetable Planting Calendar for Maricopa County (AZ1005), reviewed This information has been reviewed by University faculty.. Retrieved 2026-11-02.
University of Maryland Extension, Growing Basil in a Home Garden, Updated February 25, 2026. Retrieved 2026-11-02.
University of Delaware Cooperative Extension, Basil, October 2024. Retrieved 2026-11-02.
West Virginia University, Plant and Soil Science (Ph.D. thesis); record on Organic Eprints, Yield, pest density, and tomato flavor effects of companion planting in garden-scale studies incorporating tomato, basil, and Brussels sprout, 2004 (deposited 19 Dec 2005). Retrieved 2026-11-02.
Meeting abstract (ASA-CSSA-SSSA 2003 annual meetings abstracts collection, mirrored by Prince of Songkla University library), Do Tomatoes Love Basil But Hate Brussels Sprouts? Evaluating Popular Companion Planting Claims in Garden-Scale Studies (NE_05-bomford156693-oral), 2003. Retrieved 2026-11-02.
Penn State Extension, Herbs Make Good Plant Partners and Companions, Updated April 22, 2026. Retrieved 2026-11-02.
PLOS ONE 14(3): e0213071, Companion planting with French marigolds protects tomato plants from glasshouse whiteflies through the emission of airborne limonene, March 1, 2019. Retrieved 2026-11-02.
University of California Agriculture and Natural Resources (UCCE Master Gardener Program), Companion Planting Chart: Companion planting in the vegetable garden, File dated 2023-09 in URL path; no date printed. Retrieved 2026-11-02.