The New Almanac

USDA Zone 13b

Zone 13 · The Warmest Gardens in America

Average annual extreme minimum temperature: 65 to 70 °F (18.3°C to 21.1°C).

Lowland Puerto Rico and Hawai'i's hottest shores — winter minimums of 60 to 70°F, the top of the USDA scale. Gardening here is purely tropical: fast, continuous, and ruled by rain, wind, and pests rather than any memory of cold.

By the numbers

Median season
Year-round
ZIPs tracked
14

Medians across every ZIP we track in zone 13b, derived from NOAA 1991–2020 climate normals. Look up your own ZIP for local dates — within a zone, frost varies by weeks.

Where you'll find zone 13

Lowland Puerto Rico above all — over half of Puerto Rico ZIPs in our data sit in 13a — plus Hawai'i's warmest coastal strips. Zone 13 was added in the 2023 USDA map update; it describes places where an average winter night stays above 60°F.

Vegetables that earn their keep

  • The full year-round tropical roster (CTAHR's Hawai'i guidance applies): fast cycles of warm-season vegetables, with cool-season crops in the relatively cooler months or at elevation
  • Quick-maturing varieties fitted to heat windows (CTAHR)

Fruits & perennials that overwinter

  • Papaya at its happiest — minimum temperatures reliably above its 60°F comfort line (CTAHR)
  • Mango, avocado, banana, citrus — the complete tropical and subtropical fruit roster (UF/CTAHR)
  • No chill-requiring temperate fruit — chill hours here are zero

The top of the scale

Zone 13 is what the USDA scale looks like when winter disappears entirely: the coldest night of an average year is warmer than a summer night in Minnesota. Every cold-defined rule of mainland gardening — frost dates, chill hours, season extension — is simply absent. What remains is the tropical discipline: heat, water, wind, and an unbroken pest year.

Rain seasons instead of frost seasons

The planning calendar follows rainfall. Dry-side (leeward) gardens irrigate — papaya wants at least ~4 inches of water monthly (CTAHR) — while wet-side gardens manage the diseases that love standing humidity: Phytophthora, anthracnose, and their kin, fought with airflow, spacing, and resistant varieties (CTAHR).

Wind is structural

CTAHR treats wind as a founding constraint: steady trades deform tropical fruit trees and ~40 mph gusts uproot them in loose soils, so windbreaks precede planting. Near the shore, salt spray adds leaf desiccation; hurricane exposure in the Caribbean makes wind-resistant species choice and canopy thinning part of basic garden design (UF).

Heat has ceilings too

Even in the tropics, hotter is not always better — papaya's female sterility at 90–95°F (CTAHR) stands for a wider truth: many crops have an upper comfort line that the warmest lowlands brush against. Quick-maturing, heat-adapted varieties — and a little elevation when you can get it — are the answers.

Plant guides, timed to your frost dates

Every guide gives its planting calendar relative to your last frost — the dates above (or your ZIP's) drop straight in.

Sources