Zone 13a: Gardening in Hawaii's Warmest Spots
Zone 13a is the warmest zone on the USDA map, found in the US only in a couple of very warm, low coastal spots in Hawaii. Cold never limits plants here. The garden is shaped by heat, wind, salt and rainfall, with tropical fruit year-round and cool-season vegetables only in the mildest months.
- Coldest winter night
- 60 to 65°F
- ZIP codes in the zone
- 1
Frost in zone 13a
In 100% of zone 13a's ZIP codes with weather records, a 32°F night happens in fewer than half of years, so frost dates do not organize the gardening year. Cool-season vegetables grow from fall through spring, and heat, not frost, ends the season for many crops.
What a zone 13a winter means
Zone 13a is the warmest category on the map. There is no winter in the gardening sense: no frost, no dormancy and no chilling. USDA’s map pages describe zones 12 and 13 as a way to compare the cold sensitivity of tropical plants. For a gardener in zone 13a, the more useful questions are how hot the site gets, how much rain it receives, and how exposed it is to wind and salt spray.
Where zone 13a is
Only two ZIP codes in Hawaii fall in zone 13a on the 2023 map: the Keauhou area on the Kona coast of the Big Island and Marine Corps Base Hawaii at Kaneohe Bay on Oahu. Both are low, coastal and warm.
Fruit
Bananas grow best with warm temperatures averaging around 81°F, full sun and plentiful, well-distributed rain, in a site protected from wind (CTAHR). Fruit that needs a cool season to flower, such as lychee, is unreliable this warm.
Vegetables
Lowland heat shortens the season for cool-season crops. Grow lettuce, broccoli and cabbage in the coolest months and choose heat-tolerant cultivars; CTAHR names ‘Greenbud’ and ‘DeCicco’ broccoli for warm lowlands. Leaf lettuces handle lowland conditions better than head lettuce. For year-round planting, CTAHR’s home garden bulletin lists carrots, beets, chard, mustard greens, eggplant, green onions and beans as dependable at low elevations, notes that tomatoes do best in the cool season, and recommends okra as a warm-season crop.
Special concerns
- Wind and salt: coastal sites need shelter. A University of Hawaii Extension agent suggests a sorghum-sudangrass windbreak, which reaches about 6 feet in 40 days, and siting gardens away from the windiest north and east sides of buildings.
- Water: CTAHR advises against growing vegetables without irrigation in most of Hawaii, since even frequent showers may add up to too little rain, and notes that organic mulch reduces drought damage and the need to water.
Where zone 13a is
States with zone 13a ZIP codes, the largest first: Hawaii.
Zone 12bAll zones and the zone finder
Questions
Why did USDA add zone 13?
USDA added zones 12 and 13 to describe places whose coldest nights stay above 50°F and 60°F, found only in Hawaii and Puerto Rico. They help compare how much cold tropical plants tolerate and when to bring tropical patio plants indoors elsewhere.
What vegetables can I grow in zone 13a?
Heat-tolerant ones year-round, and cool-season crops in the mildest months. University of Hawaii CTAHR found head lettuce grows only in winter at low elevations and that high night temperatures make lettuce bitter; it recommends heat-tolerant broccoli such as 'Greenbud' and 'DeCicco' for lowlands.
Do fruit trees that need a cool winter grow in zone 13a?
Not reliably. Lychee, for example, needs a cool, dry winter of roughly 59°F days and 50°F nights to start flowers, according to CTAHR. Choose tropical fruit such as bananas and papayas that need no cool season.