In Hawaii, pick Asian greens by heat tolerance, not cold hardiness. Water spinach, amaranth, Malabar spinach and sweet potato leaves are the dependable lowland picks. Bok choy, tatsoi, mizuna and choy sum are easier at elevation, on cooler windward slopes, or in the shade, and they need quick harvests anywhere warm. The rest of this page explains why.
The short answer for Hawaii
The reference station for Honolulu shows a mean daily minimum of 66.8°F in the coldest month. Federal climate data (NOAA’s 1991-2020 Climate Normals) also records zero days per year at or below 32°F, and no freeze occurs in inhabited areas. Cold never removes a season here. Heat, rain and exposure decide which greens succeed, so sort varieties by how they handle warmth.
Heat-lovers for the lowlands
Water spinach (ong choy), amaranth (often sold as Chinese spinach), Malabar spinach and sweet potato tips grow with enthusiasm where mainland gardeners would have a short summer window. Cut-and-come-again harvesting suits them. Cutting tips keeps the plants bushy and productive rather than letting them run to seed.
Cool-season greens, with conditions
Bok choy, tatsoi, mizuna, komatsuna and choy sum are the classic stir-fry leaves. All of them lean toward cooler weather and bolt when it turns hot. In the lowlands, treat them as fast crops: sow small batches often, harvest young, and give them afternoon shade. Above the warm coast, or on cooler wetter slopes, they behave much more like they do in a mainland spring.
| Type | Examples | Warm lowlands | Best fit |
|---|---|---|---|
| Heat-loving leaves | Water spinach, amaranth, Malabar spinach, sweet potato tips | Thrive | Hot coastal and leeward gardens |
| Quick cool-season greens | Bok choy, tatsoi, mizuna, komatsuna, choy sum | Workable if shaded and harvested young | Cooler months, higher elevations, shaded beds |
| Mustards | Leaf mustards, gai choy | Pungent and quick to bolt in heat | Cooler spots; sow often |
| Heading types | Napa cabbage | Tends to struggle forming tight heads | Cool elevations only |
The timing question comes next. Since there is no frost date to count from, When to Sow Asian Greens in Hawaii works from rainfall and elevation instead, and Growing Asian Greens in Hawaii covers the wider picture of beds, watering and pests.
What will not work here
Frost-based advice
Half the Asian greens advice online is anchored to a last spring frost or a first fall frost. Here, neither exists in the places people garden. Frost shows up only on the high volcanic summits of Mauna Kea, Mauna Loa and Haleakala. A guide that says “sow six weeks before last frost” has nothing to count from, and “cold-hardy” or “overwintering” on a seed packet is irrelevant at a coldest-month minimum of 66.8°F. Shop for bolt resistance, heat tolerance and disease resistance instead.
Lowland summer cool-season crops
A bok choy sown in the lowlands in the hottest stretch of the year will usually bolt before it fills out. The plant reads heat as a signal to flower, and leaves turn bitter along the way. Napa cabbage is the clearest casualty: it wants cool nights to wrap into a dense head, and warm coastal nights rarely oblige. Plant it only where elevation brings real cool, and otherwise grow looser, faster types.
Weekly watering on the dry side
A leeward lowland garden in a dry spell punishes a weekly soak. Asian greens are shallow-rooted and fast, and a bed that dries out between waterings stresses plants into bitterness or early flowering. Frequent light watering plus mulch fits them far better than one deep drink. Drip lines on a timer pay for themselves quickly here.
Tight spacing on the wet side
The opposite problem hits windward gardens. Constant moisture and humid air mean crowded rows stay wet, which invites leaf rot and gives slugs and snails somewhere to hide. Space plants wider than a seed packet suggests, raise the beds, and keep leaves off bare soil. Slugs are also worth respecting for a health reason: Hawaii has rat lungworm, so wash leafy greens thoroughly before eating, and check the Hawaii Department of Health for current guidance.
What changes across Hawaii
The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) places Hawaii in zones 9a through 13a. That is four full zones apart, and the system rests on one variable only: the average annual extreme minimum temperature. So there is no single Hawaii answer. The Honolulu figure above describes a warm coastal city, not the cooler upper slopes where a gardener is working with a different climate entirely.
If you garden at higher elevation, or on a cooler, rainier windward side, shift toward the cool-season group. Bok choy, tatsoi and komatsuna get an easier run there, and sowings can be spaced more generously across the year. Heat-lovers like water spinach and amaranth will still grow, but they slow down as nights cool, so give them your warmest, most sheltered bed.
If you garden on a hot, dry leeward coast, flip that. Lean on the heat-lovers, treat the cool-season greens as shade-cloth crops, and plan irrigation before you plan varieties. Rainfall and exposure differ sharply over short distances in the islands, which is why two gardens on the same island can need different plans.
This page does not tell you which zone your own garden sits in. Look up your location on the USDA Plant Hardiness Zone Map, then read the zone as a clue to cool-versus-warm, not as a sowing date.
Where to check this for your own county
The best next stop is University of Hawaii CTAHR Cooperative Extension, the land-grant extension service for the state. Look for two things: a local planting calendar for your island or county, and the varieties that have actually been trialled where you live. A trialled variety is not just a seed catalog claim. It has been grown, watched and compared in real island conditions.
Ask extension staff about elevation, since a variety that sails through at sea level may sulk a few hundred feet up, and the reverse. Also ask about local pest pressure, particularly slugs and leaf-eating insects, because the advice for dry leeward gardens and soggy windward ones can differ.
A county recommendation beats a state one, and this page is the state one. It sorts varieties by type and explains the logic. It does not have county rainfall figures, elevation breakpoints or a local trial list, and it should not pretend to. Use it to know what to ask, then let your county office supply the specifics.
Checking this against your own garden
Your own observations outrank every date and variety list here, and three of them are easy to collect without buying anything.
- Soil warmth by feel. Push your hand into the bed in the morning. Soil that feels cool tells you that you are in the cooler, slower end of the range, where cool-season greens are comfortable. Soil that already feels warm early in the day points to heat-lover territory.
- The first flower stalk. Sow a small test row of bok choy or mizuna and watch for the center shoot lengthening. If it bolts early, your spot runs hot for that crop, and shade or a different variety is the fix. Male flowers appearing on a neighbor’s squash or cucumber early in the season point the same direction.
- The first true leaves. Time how long seedlings take to put out their first true leaves after sprouting. Fast means a warm microclimate, and you should plan for quick harvests. Slow means a cooler, wetter or more shaded spot, where you can be more patient.
Write the dates in a notebook for one year. By the second sowing you will know more about your garden than any state-level page can tell you.
Common questions
Do I need frost protection for Asian greens in Hawaii?
No, not in the places people garden. Frost occurs only on the high summits of Mauna Kea, Mauna Loa and Haleakala. Plan around heat, rainfall and exposure instead.
Can I grow bok choy in the lowlands?
Yes, with conditions. Give it afternoon shade, keep the soil evenly moist, sow small batches often and harvest young before heat triggers flowering. Cooler months and higher elevations are easier.
Which Asian greens are the easiest in Hawaii?
Heat-lovers such as water spinach, amaranth, Malabar spinach and sweet potato tips are the most forgiving in warm lowland gardens. They keep producing when cool-season greens would bolt.
Is there a best month to sow?
Not by frost date, since there is none. Timing depends on rainfall, elevation and which side of the island you are on. See When to Sow Asian Greens in Hawaii for how to read those signals.