Hawaii’s year-round growing season lets you plant onions any month, but rainfall patterns guide the best timing. The best time to plant onions in hawaii depends on your island’s specific microclimate and whether you want bulb onions or green onions. This guide breaks down everything you need to know for a successful onion crop in the Aloha State.
Onions are surprisingly easy to grow in Hawaii’s warm soil. They just need the right start. Let’s walk through the timing, varieties, and steps to get it right.
Best Time To Plant Onions In Hawaii
The ideal window for planting bulb onions in Hawaii is from October through December. This timing allows onions to grow during the cooler, drier months. They bulb up as days get longer in spring. Green onions, or scallions, can be planted almost any time of year.
Why this window works so well: Onions are day-length sensitive. They need longer days to form bulbs. In Hawaii, day length changes less than on the mainland. But the cool season still gives you the best results for storage onions.
Understanding Hawaii’s Growing Zones
Hawaii has many microclimates. What works in Honolulu may not work in Hilo or upcountry Maui. Here’s a quick breakdown:
- Leeward sides (dryer, like Kona, Waikiki): Plant from October to December. Less rain means less rot.
- Windward sides (wetter, like Hilo, Hanalei): Plant from September to November. Avoid heavy winter rains.
- Higher elevations (above 2,000 feet, like Volcano, Kula): Plant from March to May. Cooler temps allow spring planting.
Check your local rainfall averages. Onions hate wet feet. Too much rain causes fungal diseases. If you get over 100 inches of rain a year, consider raised beds or containers.
Short-Day Onion Varieties For Hawaii
Hawaii is a short-day onion region. This means onions start bulbing when days reach about 10-12 hours. You need varieties bred for this. Here are top performers:
- Texas Grano 1015Y: Sweet, large bulbs. Very reliable in Hawaii.
- Red Creole: Pungent, stores well. Great for cooking.
- Walla Walla: Sweet but needs cooler temps. Best at higher elevations.
- White Bermuda: Mild, good for salads. Quick to mature.
- Yellow Granex: The classic Vidalia type. Very sweet.
Do not plant long-day varieties. They won’t bulb properly in Hawaii’s short days. Stick with short-day or intermediate types.
Planting Green Onions (Scallions) Year-Round
Green onions are much more forgiving. You can plant them any month. They don’t need specific day length. Just keep them watered and harvest when tops are 6-8 inches tall.
Best green onion varieties for Hawaii:
- Evergreen Bunching: Hardy, perennial-like. Keeps producing.
- White Lisbon: Classic scallion. Quick to harvest.
- Red Beard: Purple-tinged stems. Attractive in salads.
Plant green onions every 3-4 weeks for a continuous supply. They grow fast in warm soil. You’ll have fresh scallions in 60-70 days.
Step-By-Step Planting Guide
Follow these steps for the best results. Onions are not fussy, but they do need consistent care.
1. Choose Your Method: Seeds Vs. Sets Vs. Transplants
You have three options for starting onions in Hawaii:
- Seeds: Cheapest, widest variety. Takes longer (3-4 months to harvest). Start indoors or in a shaded nursery bed.
- Sets: Small bulbs sold in bundles. Faster (2-3 months). More expensive but easier. Look for short-day sets.
- Transplants: Seedlings from a nursery. Fastest (6-8 weeks to harvest). Most reliable for beginners.
For bulb onions, transplants or sets work best in Hawaii’s warm weather. Seeds can struggle with heat and damping-off disease.
2. Prepare The Soil
Onions need loose, well-draining soil with a pH of 6.0-7.0. Hawaii’s volcanic soil is often acidic. Add lime if needed. Mix in plenty of compost or aged manure.
Key soil prep steps:
- Remove rocks and debris. Onions need room to expand.
- Add 2-3 inches of organic matter. Turn it in 6-8 inches deep.
- Apply a balanced fertilizer (10-10-10) at planting time. Use about 1 cup per 10 feet of row.
- Rake the bed smooth. Onions need a fine, crumbly surface.
Raised beds are ideal for wet areas. They improve drainage and warm up faster in cooler months.
3. Plant At The Right Depth And Spacing
Planting depth matters. Too deep and bulbs rot. Too shallow and they dry out.
- Sets and transplants: Plant 1 inch deep. Space 4-6 inches apart for large bulbs. Closer spacing gives smaller onions.
- Seeds: Sow 1/4 inch deep. Thin to 4 inches apart when seedlings are 3 inches tall.
- Rows: Space rows 12-18 inches apart. This allows weeding and airflow.
Press the soil gently around each onion. Water well after planting. Keep soil consistently moist but not soggy.
4. Water And Fertilize Correctly
Onions have shallow roots. They need regular water. In Hawaii, this means 1-2 inches per week from rain or irrigation. Use drip irrigation to keep foliage dry. Wet leaves invite disease.
Fertilizing schedule:
- At planting: Apply a starter fertilizer high in phosphorus.
- 3 weeks after planting: Side-dress with nitrogen. Use blood meal or fish emulsion.
- Every 3-4 weeks: Continue feeding until bulbs start swelling. Stop once tops begin to yellow.
Do not over-fertilize with nitrogen. It produces lush tops but small bulbs. Balance is key.
5. Manage Weeds And Pests
Weeds compete with onions for nutrients. Keep beds weed-free. Hand-pull carefully to avoid disturbing onion roots. Mulch with straw or grass clippings to suppress weeds.
Common pests in Hawaii:
- Thrips: Tiny insects that suck sap. Use neem oil or insecticidal soap.
- Onion maggots: Larvae that tunnel into bulbs. Rotate crops. Use row covers.
- Slugs and snails: Common in wet areas. Hand-pick or use iron phosphate bait.
Diseases like purple blotch and downy mildew thrive in Hawaii’s humidity. Space plants for airflow. Avoid overhead watering. Remove infected leaves promptly.
Harvesting And Storing Onions
Knowing when to harvest is crucial. Bulb onions are ready when tops fall over and turn brown. This usually happens 100-150 days after planting, depending on variety.
How To Harvest
- Stop watering when tops start falling. This helps bulbs cure.
- Gently loosen soil around bulbs with a fork. Do not pull by the tops.
- Lift onions and let them sit in the field for 2-3 days if weather is dry. Or move them to a shaded, airy spot.
- Once tops are fully dry, cut them off 1 inch above the bulb. Trim roots.
For green onions, harvest when stems are 6-8 inches tall. Pull the whole plant. Use immediately or store in the fridge for up to a week.
Curing And Storing Bulb Onions
Curing is essential for long storage. It toughens the outer skin and prevents rot. Cure in a warm (75-85°F), dry, well-ventilated area for 2-3 weeks. A garage or lanai works well in Hawaii.
After curing, store onions in a cool, dark place. Ideal temperature is 40-50°F. Do not store in plastic bags. Use mesh bags or baskets for airflow.
Sweet onions like Texas Grano store only 2-3 months. Pungent varieties like Red Creole can last 6-8 months. Check regularly for soft spots.
Common Mistakes And How To Avoid Them
Even experienced gardeners make errors. Here are the most common ones in Hawaii:
- Planting too late: If you plant in January or February, bulbs may not form before hot weather. Stick to October-December.
- Overwatering: Hawaii’s rain can be heavy. Onions rot quickly in wet soil. Use raised beds and well-draining soil.
- Wrong variety: Long-day onions will not bulb. Always choose short-day types.
- Planting too deep: Bulbs need to sit at soil surface. Deep planting causes elongated necks and rot.
- Skipping fertilizer: Onions are heavy feeders. Without nutrients, bulbs stay small.
Learn from these mistakes. Your next crop will be better.
Frequently Asked Questions
Can I plant onions in Hawaii during summer?
Yes, but only green onions. Bulb onions planted in summer usually produce small bulbs or none at all. The heat and rain cause bolting and disease. Stick to the cool season for bulbs.
What is the best onion variety for Hawaii’s wet side?
Red Creole is the most disease-resistant. It handles humidity well. Texas Grano also works but needs good drainage. For wet areas, use raised beds to avoid waterlogging.
How long do onions take to grow in Hawaii?
Bulb onions take 100-150 days from planting to harvest. Green onions are faster, at 60-70 days. Transplants speed up the process by 3-4 weeks compared to seeds.
Do I need to fertilize onions in Hawaii’s volcanic soil?
Yes. Volcanic soil is rich in some minerals but low in nitrogen and phosphorus. Onions need regular feeding. Use a balanced fertilizer every 3-4 weeks during growth.
Can I grow onions from kitchen scraps in Hawaii?
Yes, for green onions. Plant the root ends of store-bought scallions in soil. They regrow quickly. For bulb onions, it’s less reliable. Better to use sets or seeds.
Final Tips For Success
Onions are rewarding to grow in Hawaii. The key is timing. Plant bulb onions from October to December. Choose short-day varieties. Prepare soil well. Water consistently but avoid overdoing it.
For green onions, plant any time. They are the easiest entry point for beginners. Harvest them young for the best flavor.
Rotate your onion crops each year. Do not plant them in the same spot more than once every three years. This prevents soil-borne diseases.
Watch for signs of stress. Yellowing leaves may mean too much water. Small bulbs mean not enough sun or nutrients. Adjust as needed.
With these guidelines, you can enjoy fresh, homegrown onions year-round. Start planning your planting window now. Your taste buds will thank you.
Remember, the best time to plant onions in Hawaii is during the cooler, drier months. But with the right care, you can extend the season. Happy growing in paradise.