Hawaii has no frost calendar, so there is no “after the last frost” date to wait for. Sow warm-season grass seed when the soil two inches down reads 65 °F and rising, and you can keep the seedbed damp. In most lowland yards that describes a good part of the year. Rainfall, elevation and which side of the island you live on decide the rest. For the general method, see Starting a New Lawn From Seed.
The best time to sow grass seed in Hawaii
Mainland seeding advice hangs on frost. Count back from the first fall freeze, count forward from the last spring one. Here that arithmetic has nothing to work with. NOAA’s 1991-2020 Climate Normals for the station used here record zero days per year at or below 32 °F, and the freeze percentiles come back flagged as not computable. Frost does occur on the high summits of Mauna Kea, Mauna Loa and Haleakala. It never reaches the places where people mow.
That is one station, so treat it as a description of the lowlands, not a promise for every lot. What it does tell you is that the calendar question changes. You are no longer asking “is it too cold?” You are asking “will this seedbed stay wet, and is the soil warm enough?”
Windward, leeward and the rain you can count on
Seed germinates only while the surface stays damp. On a windward slope, where trade-wind showers arrive most weeks, you can sow in nearly any month and let the weather do much of the watering. The risk there is the opposite one: a heavy downpour right after sowing can wash seed into low spots. On a leeward coast, the weather will not help. Sowing in the wetter winter months lowers your water bill and your failure rate, and sowing in a dry stretch means committing to irrigation for weeks.
Elevation and the soil thermometer
Warm-season seed wants soil at 65 to 70 °F and rising. Push a thermometer two inches into the ground in mid-morning. At sea level you will usually clear that bar. Climb to cooler upcountry elevations and you may not, particularly on cloudy, misty days. If the reading is under 65 °F and not climbing, wait for a warmer spell.
This also settles the choice of grass. The species that work here are all warm-season types: Bahiagrass, Bermudagrass, Carpetgrass, Centipedegrass, Seashore Paspalum, St. Augustinegrass and Zoysiagrass. Cool-season grasses are built to grow in mild weather and rest through cold. Without a cold season, they spend the year under heat stress and give ground to weeds. They will not hold a lawn here.
The last date that still works
On the mainland, the rule of thumb is about 45 days of growing weather before the first fall freeze. Seed sown later germinates, then dies over winter. In Texas, that rule yields a firm cutoff (see When to Plant Grass Seed in Texas), and in Ontario it arrives even sooner (When to Plant Grass Seed in Ontario). In inhabited Hawaii the freeze never comes, so there is no cutoff date to count back from.
Something else takes over as the deadline: the 45 days still have to be real growing days. In the lowlands, they are available in any month, because the soil stays warm. The cutoff there is practical. Do not start a new lawn if you cannot water it daily for the first few weeks, and do not start one on the eve of a stretch you know will be dry.
At higher elevations, the cutoff is the soil thermometer. If your readings sit below 65 °F and are not trending up, the seed will sit, rot or germinate so slowly that weeds get ahead of it. I would not put a specific date on that for any upcountry area, because the temperature gap between neighboring elevations can be large, and no figure for it is published here. Your own readings, taken the same way for a week, are more reliable than any calendar.
One more timing factor is the season’s rain pattern in your area. If you are on a leeward lot and heavy rain is the one thing you can count on, schedule sowing just ahead of the wetter months. That gives you the most natural watering for the 45 days of establishment.
Seed rate and soil preparation
Rates below are pounds per 1,000 square feet for a new lawn, and they differ a lot by species. Overseeding an existing lawn takes half. More seed is not insurance. Crowded seedlings compete with each other and thin out.
| Grass | New-lawn rate (per 1,000 sq ft) |
|---|---|
| Bahiagrass | 5 to 10 lb |
| Bermudagrass | 1 to 4 lb |
| Carpetgrass | 1 lb |
| Centipedegrass | 0.25 to 1 lb |
| Zoysiagrass | 1 to 2 lb |
| Seashore Paspalum | Sod, sprigs or plugs only, not seed |
| St. Augustinegrass | Sod, sprigs or plugs only, not seed |
Depth matters more than most people expect. Cover seed with no more than 0.25 inch of soil, then press it down so the seed touches the ground. Seed buried deeper often never emerges, and that is the single most common reason a new lawn comes up patchy. Rake lightly, roll or tamp, and stop.
For soil, the one that USDA lists as representative of Hawaii is the Hilo series, a volcanic-ash Andisol. Its mapped surface is light and porous, unusually good at holding both water and phosphorus, and well drained. Surface pH is about 5.8, slightly acid. The texture is 10 percent sand, 35 percent clay and 55 percent silt, with organic matter about 9.0 percent (USDA NRCS Soil Data Access, queried 2026-08-29). That tells you what ground here tends to do: drain freely while still holding moisture.
It does not tell you what your yard does. Hawaii spans hundreds of soil series, and a lot that a builder has scraped or filled will differ from the mapped surface. Treat those numbers as a regional tendency, not your pH. A soil test through CTAHR Extension at the University of Hawaii gives you your own figures before you spend money on amendments. Then loosen the top few inches, remove rocks and old roots, and level the surface.
Watering a new lawn until it holds
Seed that dries out after it has begun to germinate is lost. That is why watering, not sowing, is where most Hawaii lawn projects fail. The goal is a surface that stays damp, not soaked, from the day you sow until the seedlings are visibly rooted.
On a leeward lot, expect to water lightly several times a day in the first couple of weeks, since a sunny, windy surface can dry out between visits. Short passes beat one long soak, which can wash seed around and leave puddles in the low spots. On a windward lot, check the ground by hand before you run the sprinkler. If the showers kept it damp, skip the cycle.
Once the seedlings are up and have filled in, begin stretching the time between waterings and make each one deeper. This pushes roots down instead of leaving them in the top inch. How fast you taper depends on your soil and your exposure, so let the grass tell you. Color that dulls and blades that stay folded after you walk across them are a call for water.
Keep foot traffic off the new lawn, and set the mower on its highest setting for the first cuts. Expect thin patches in the early weeks. Sow a little extra seed over bare spots at the same shallow depth, and keep those spots damp too.
Common questions
Can I plant grass seed in Hawaii any month of the year?
In the lowlands, often yes, because there is no freeze season to avoid. The limits are water and soil temperature. Sow when the soil at two inches reads 65 °F and rising, and when you can keep the seedbed damp.
Do I need to wait for frost to pass?
No. NOAA’s 1991-2020 normals show zero days per year at or below 32 °F at the station used here, and frost occurs only on the high summits. Do not build a frost-based schedule.
Can I grow a cool-season grass instead?
It is a poor bet. Cool-season grasses are suited to mild weather and rest through cold, and they struggle under constant warmth. Choose from the warm-season list: Bahiagrass, Bermudagrass, Carpetgrass, Centipedegrass, Seashore Paspalum, St. Augustinegrass or Zoysiagrass.
How much seed do I need to overseed an existing lawn?
Half the new-lawn rate. For Bermudagrass, that works out to 0.5 to 2 lb per 1,000 square feet. Seashore Paspalum and St. Augustinegrass are not grown from seed, so those lawns are patched with sod, sprigs or plugs.