Basil in Zone 4a & 4b

Ocimum basilicum

When to plant basil in zone 4b

Zones 4a and 4b share the same average frost dates in our data, so this page covers both.

Method: Start indoors: Start indoors from seed, then transplant outside. Basil needs a head start most zones can't give it by direct-sowing alone.

Start indoors	Apr 3–Apr 10
Direct sow / transplant outside	May 29–Jun 5
Estimated harvest	Jul 28–Aug 4 (~60 days after transplanting)

Spacing: 4 per square foot (square-foot-gardening spacing). Mature height: 1-2 ft.

Basil is arguably the best value crop in a home garden: a single plant produces far more than the tiny, expensive plastic clamshells at the grocery store, and fresh-cut basil's flavor fades within days of harvest, so growing your own is a genuine upgrade over what a grocery-store clamshell gets you, well beyond the money saved.

How basil fits zone 4's season

Zone 4b's frost-free window runs about 128 days, from May 15 to September 20. Basil needs about 60 days from transplant to first harvest.

Good companions

Tomato: Reputed to improve tomato flavor and repel pests, but a multi-year, garden-scale controlled trial found no consistent taste preference in blind tests, and no pest-reduction benefit — treat this as one of companion planting's least-supported popular claims.
Pepper: Reputed to repel aphids and improve growth nearby, but the same controlled trial that tested basil's tomato pairing found no pest-reduction benefit on a related crop, and even higher pest counts in one case — treat this as unproven.

Where to buy basil seeds

See why we recommend these suppliers →

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