Go tropical. In Hawaii’s lowlands, the best unusual roots are the ones that like constant warmth and never need a cold spell: taro, sweet potato, cassava, ginger and turmeric. Cool-season roots such as burdock and parsnip are the gamble, and they belong at elevation if anywhere. Rainfall, elevation and windward versus leeward exposure decide the rest, because frost dates do not exist where people garden.
The short answer for Hawaii
Start with the number that settles hardiness. At the Honolulu reference station, the mean daily minimum of the coldest month is 66.8°F (NOAA NCEI Climate Normals, 1991-2020). That is the average low in the coldest month, not a record, and it means winter nights barely register for a tropical root.
The frost figures say the same thing. A frost date is the probability of a freeze by a given day, and NOAA’s normals for the station show zero days per year at or below 32°F. The freeze percentiles at 32°F and 36°F come back as “not computable,” because no freeze occurs in inhabited areas. Frost reaches only the high volcanic summits (Mauna Kea, Mauna Loa, Haleakala). So there is no frost-based sowing window to give you. Timing here follows rainfall and exposure, which the When to Plant Unusual Roots in Hawaii page covers.
That leaves the decision to be made by type. This table sorts the main groups by how well they match the islands’ heat and season length.
| Type | Examples | Fit in Hawaii |
|---|---|---|
| Warm-season starchy roots | Taro (kalo), sweet potato, cassava, purple yam | Best bets in the lowlands. Long warm seasons suit them, and taro and sweet potato have deep local track records. |
| Rhizomes | Ginger, turmeric | Strong choices where soil drains well and rain is regular. |
| Cool-season roots | Daikon, beet, carrot, burdock, parsnip | Workable at elevation or in the coolest, driest stretch of the year. The lowlands are a poor match for the slowest ones. |
| Andean tubers | Yacon, oca | Experimental. Treat as a cooler, higher-ground project and check what has been trialed. |
If you only plant one thing, make it taro or sweet potato. Both have been grown in these islands for a very long time, and nothing about the climate works against them. For a wider overview of the topic, see Growing Unusual Root Crops in Hawaii.
What will not work here
Roots that depend on cold fail first. Parsnips, horseradish and salsify build their sweetness and flavor through a stretch of chilly weather. With a coldest-month typical night of 66.8°F and no freeze at all in inhabited areas, a lowland bed never delivers that signal. You get a root, but a bland, sometimes woody one. Anything sold as “improved by frost” is out.
Weekly watering defeats the leeward side. Leeward coasts get far less rain than windward ones, and taro is a thirsty plant even in its dryland forms. A garden watered once a week by hand or on a lazy timer will give you stunted corms and leaves that droop by afternoon. Either mulch heavily and water on a schedule built around the soil, not the calendar, or pick a drier-tolerant crop like sweet potato.
Windward exposure brings the opposite problem. Constant rain and humid air punish close spacing: foliage stays wet, fungal disease moves between touching plants, and ginger or sweet potato rhizomes can rot in soil that never drains. Space generously, plant on raised rows or mounds, and skip heavy clay beds that hold water. Mainland spacing charts, written for drier air, often pack plants too tightly for a windward slope.
Finally, the speed of the season works against anything labeled “fast.” Without a frost to end the year, nothing forces a crop to finish. Cool-season roots bolt or go fibrous when warm weather lingers, and daikon left in the ground past its prime turns pithy. Warm-season roots keep growing, which is why harvest is a judgment call, not a deadline.
- Parsnip, horseradish and salsify: they need chill that lowland Hawaii never supplies.
- Taro on a weekly watering schedule: it dries out on leeward sites.
- Tightly spaced ginger or sweet potato on windward slopes: rot and leaf disease follow.
What changes across Hawaii
Hawaii is not one garden. The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) spans 9a to 13a across the state. That is a wide spread, and there is no single zone to quote. The system rests on one variable, the average annual extreme minimum temperature, so the low end of the range reflects the cold of high ground and the high end reflects warm coastal lowlands. Honolulu is the reference city for the 66.8°F figure above, and other parts of the state differ from it.
If you garden at elevation, such as upcountry Maui or the cooler slopes of Hawaii Island, shift toward the cool side of the table. Daikon, carrots, beets and burdock become realistic, and the cold-sensitive tropical roots slow down or sulk. Ginger and cassava are the ones to treat cautiously there. Plant the warm-season roots in the sunniest, most sheltered spot you have.
If you garden on a windward coast, including the north-facing shores, your problem is moisture, not temperature. Prioritize drainage, raised beds and wider spacing. Taro tolerates wet conditions well, which makes it an obvious fit where other crops rot.
On a dry leeward coast, flip that logic: choose drought-tolerant sweet potato and cassava, mulch deeply, and set up irrigation you can rely on.
Nobody can tell you your zone from a web page. Look up your own address on the USDA Plant Hardiness Zone Map and then read the zone against your actual conditions: a sheltered lowland yard and a windy ridge a few miles away can sit in very different places on that scale.
Where to check this for your own county
The county office is the next stop. The University of Hawaii College of Tropical Agriculture and Human Resources (CTAHR) Extension is the state’s land-grant extension service, and it staffs offices across the islands that know your local rainfall, soils and pest pressure.
Two things to look for there. First, the local planting calendar for your area: because timing in Hawaii follows rainfall and elevation instead of frost, a calendar written for your side of the island is worth far more than any statewide guideline. Second, the varieties trialed in your county. Taro and sweet potato come in many cultivars, and the ones that resist disease or tolerate your rainfall are exactly what a local trial reveals.
A county recommendation beats a state one. This page is the state one, and it works by type and by climate pattern, not by your specific valley. This page does not carry a county-by-county calendar or variety list, so for those details rely on extension staff and published local trials.
When you contact them, bring your elevation, which side of the island you are on, and a description of your soil (does it stay wet, dry fast, crack in summer?). Those three details let an agent answer in a sentence what would take pages here. Many offices also run workshops or plant sales where you can see the varieties that do well nearby.
Checking this against your own garden
Your own observation outranks every date on this page. Three things are worth watching, and none needs equipment.
Soil warmth by feel. Push your hand a few inches into the bed in the morning. If the soil feels distinctly cool, you are likely at higher elevation or in a shaded, windy spot, and warm-season roots like ginger and cassava will sulk. If it feels warm and slightly damp, you are in tropical-root territory.
The first true leaves. Sow a quick test row of daikon or carrots and note how long the first true leaves (the ones after the rounded seed leaves) take to appear. Quick, even emergence points to a warm, moist site. Slow or patchy emergence suggests the soil is cooler, or that it dries out between rains.
The first male flowers. Plant a squash or a few corn plants nearby as a calendar. When the first male flowers open, you have a living measure of how fast your spot warms and grows. If they arrive late compared with neighbors at a lower elevation, expect your root crops to run slower too, and choose varieties accordingly.
Keep notes for a season or two. That record, more than any chart, tells you which type from the table above belongs in your bed.
Common questions
What is the easiest unusual root to grow in Hawaii?
Sweet potato and taro are the safest starting points. Both suit the lowland heat, and both have long histories in the islands. Pick sweet potato for drier sites and taro where water is plentiful.
Do I need to worry about frost when planting roots?
Not in inhabited areas. NOAA’s 1991-2020 normals show zero days per year at or below 32°F at the reference station, and frost occurs only on the high volcanic summits. Rainfall, elevation and exposure set your timing instead.
Can I grow carrots, beets or parsnips in Hawaii?
Carrots and beets can work, especially at elevation or in the cooler season. Parsnips are harder because they rely on chill for flavor, and the lowlands do not supply it.
Which USDA zone is Hawaii in?
The USDA Plant Hardiness Zone Map (2023) covers 9a to 13a for the state, so there is no single answer. Check the map for your own address.