Hawaii’s tropical climate allows for year-round rhubarb planting in shaded, higher elevations, but the best time to plant rhubarb in hawaii is during the cooler, drier months from October to February. This timing helps the plants establish strong roots without the stress of intense heat or heavy rain.
Best Time To Plant Rhubarb In Hawaii
Rhubarb is not a typical tropical crop, but it can thrive in Hawaii’s cooler microclimates. The key is understanding your specific elevation and rainfall patterns. Most successful plantings happen above 2,500 feet where nights are cooler.
Planting during the fall and early winter gives your rhubarb a head start. The soil is still warm from summer, but the air temperature is lower. This combination encourages root growth before the plant puts energy into leaves.
Why October Through February Works Best
During these months, Hawaii experiences shorter days and lower temperatures. Rhubarb needs a period of cool weather to break dormancy and produce thick stalks. Even in Hawaii, a few weeks of cooler nights (below 60°F) can trigger better growth.
- Less humidity means less fungal disease
- Lower rainfall reduces root rot risk
- Cooler nights mimic the plant’s natural cycle
- Young plants avoid the hottest summer sun
If you plant in summer, your rhubarb may survive but produce thin, tough stalks. The heat can cause the plant to bolt (flower early) which reduces harvest quality.
Elevation Matters More Than Season
In Hawaii, elevation often determines success more than the calendar date. Rhubarb grows best between 2,500 and 5,000 feet. At these heights, nighttime temperatures regularly drop below 65°F even in summer.
For lower elevations (below 1,500 feet), the best time to plant rhubarb in hawaii shifts to December through February. You need the coolest possible window to give the plants a chance. Even then, expect smaller harvests and more maintenance.
Ideal Elevation Zones For Rhubarb
- Above 3,500 feet: Plant anytime from September to March
- 2,500 to 3,500 feet: Plant October to February for best results
- 1,500 to 2,500 feet: Plant only November to January
- Below 1,500 feet: Not recommended, but try December planting with heavy shade
Preparing Your Rhubarb Planting Site
Before you buy rhubarb crowns, prepare the soil properly. Rhubarb is a heavy feeder and needs rich, well-draining soil. In Hawaii’s volcanic soils, you may need to amend heavily.
Choose a spot that gets morning sun but afternoon shade. Full sun in Hawaii can scorch rhubarb leaves. A north or east-facing slope is ideal.
Soil Requirements For Hawaiian Rhubarb
Rhubarb prefers a pH between 5.5 and 6.5. Most Hawaiian soils are naturally acidic, so test your soil first. Add lime if the pH is below 5.5.
- Mix in 3 to 4 inches of compost
- Add aged manure for nitrogen
- Ensure drainage is excellent – rhubarb hates wet feet
- Remove all rocks and large debris
If your soil is heavy clay (common in some areas), build raised beds. This prevents waterlogging during Hawaii’s rainy periods. Raised beds also warm up faster in the cooler months.
Choosing Rhubarb Varieties For Hawaii
Not all rhubarb varieties perform well in tropical climates. You need heat-tolerant types that don’t require long cold periods. Here are the best choices:
- Victoria: Classic variety, reliable in warm climates
- Raspberry Red: Sweet stalks, good heat tolerance
- Valentine: Produces well with minimal chill hours
- Glaskins Perpetual: Can be harvested longer in warm weather
Avoid varieties like Canada Red or Cherry Red that need extended cold. They will struggle in Hawaii unless you’re above 4,000 feet.
Step-By-Step Planting Guide
Follow these steps for the best time to plant rhubarb in hawaii. Timing your planting correctly is only half the battle – proper technique ensures strong growth.
- Dig holes 2 feet apart and 12 inches deep
- Mix in a handful of balanced fertilizer (10-10-10)
- Place the crown so the buds are 1-2 inches below soil surface
- Backfill gently, pressing soil around roots
- Water thoroughly after planting
- Add a 2-inch layer of mulch (straw or wood chips)
Water deeply once a week, more if the weather is dry. Rhubarb needs consistent moisture but not saturation. In Hawaii’s rainy season, you may need to water less.
Mulching Is Critical In Hawaii
Mulch does three things for rhubarb in Hawaii: keeps soil cool, retains moisture, and suppresses weeds. Use organic mulch like shredded leaves or pine needles. Avoid fresh grass clippings that can heat up as they decompose.
Replenish mulch every 3 months. In warmer areas, a thicker mulch layer (3-4 inches) helps keep roots cool during summer.
Caring For Rhubarb Throughout The Year
Once planted, rhubarb needs regular care. The best time to plant rhubarb in hawaii is just the start. Ongoing maintenance determines your harvest quality.
Fertilizing Schedule
Rhubarb is hungry. Feed it every 6 weeks during the growing season. Use a balanced fertilizer or side-dress with compost.
- First feeding: 4 weeks after planting
- Second feeding: When stalks begin to grow
- Third feeding: After first harvest
- Stop fertilizing by September to let plants rest
Too much nitrogen produces lush leaves but thin stalks. Stick to balanced formulas. If leaves look pale, add a bit more nitrogen.
Watering In Hawaii’s Climate
Hawaii’s rainfall varies dramatically by location. On the windward side, you may get 100+ inches annually. On leeward sides, much less. Adjust watering accordingly.
The rule: keep soil moist but not soggy. Stick your finger 2 inches into the soil. If it feels dry, water. If wet, wait. Overwatering is the most common mistake.
Signs Of Overwatering
- Yellowing leaves
- Soft, mushy stalks
- Fungal growth on soil surface
- Stunted growth
If you see these signs, reduce watering and improve drainage. Consider moving the plant to a raised bed if problems persist.
Harvesting Rhubarb In Hawaii
You can start harvesting rhubarb about 1 year after planting. In Hawaii’s climate, you may get 2-3 harvests per year if conditions are right.
Harvest only when stalks are 12-18 inches long and firm. Never take more than one-third of the stalks at a time. This keeps the plant healthy.
How To Harvest Properly
- Grasp the stalk near the base
- Pull gently while twisting slightly
- The stalk should snap free cleanly
- Cut off the leaf (leaves are toxic)
- Rinse stalks and store in refrigerator
Do not use a knife to cut stalks. Pulling encourages new growth. Cutting can leave stubs that rot.
When To Stop Harvesting
Stop harvesting by early summer if you planted in fall. This gives the plant time to rebuild energy for the next season. In Hawaii, you may get a second harvest in late fall if temperatures stay cool.
If stalks become thin or stringy, stop harvesting immediately. The plant is stressed and needs rest. Let it grow undisturbed for 2-3 months.
Common Problems Growing Rhubarb In Hawaii
Even with the best time to plant rhubarb in hawaii, issues can arise. Here are the most common problems and solutions.
Bolting (Flowering)
Rhubarb bolts when stressed by heat or drought. The plant sends up a flower stalk, which reduces stalk quality. Remove flower stalks immediately when you see them.
To prevent bolting: provide afternoon shade, mulch heavily, and water consistently. Choose bolt-resistant varieties like Victoria.
Pests In Hawaii
Rhubarb has few pests in Hawaii, but watch for these:
- Slugs and snails: Use beer traps or copper tape
- Aphids: Spray with neem oil or strong water stream
- Root weevils: Apply beneficial nematodes to soil
Most pest problems are minor. Healthy plants resist attacks better. Keep your rhubarb well-fed and watered.
Fungal Diseases
Hawaii’s humidity promotes fungal issues. Leaf spot and crown rot are most common. Prevent them by:
- Watering at soil level, not on leaves
- Providing good air circulation
- Removing dead leaves promptly
- Using fungicide only as last resort
If crown rot occurs, dig up the plant and discard. Do not replant rhubarb in the same spot for 3 years.
Extending The Growing Season
In lower elevations, you can extend rhubarb’s productive season with a few tricks. These help even when the best time to plant rhubarb in hawaii has passed.
Using Shade Cloth
Install 50% shade cloth over your rhubarb bed. This reduces leaf temperature by 10-15°F. It also lowers water evaporation. Use PVC hoops to create a simple structure.
Shade cloth is essential for areas below 2,000 feet. Without it, rhubarb will go dormant in summer. With shade, you can harvest into June or July.
Container Growing
Grow rhubarb in large containers (at least 20 gallons). This lets you move plants to cooler spots during hot spells. Place containers on the north side of your house for maximum shade.
Container rhubarb needs more frequent watering and fertilizing. Check soil moisture daily during warm weather. Use a high-quality potting mix with added compost.
Rhubarb Varieties For Different Hawaiian Islands
Each Hawaiian island has unique microclimates. Here’s what works best where:
Big Island (Hawaii)
Best areas: Waimea, Volcano, and upper Puna. Plant from October to February. Use Victoria or Raspberry Red. Elevations above 3,000 feet are ideal.
Maui
Best areas: Kula and upcountry. Plant November to January. Valentine variety does well here. Provide afternoon shade in summer.
Oahu
Best areas: North Shore mountains and Tantalus. Plant December to February. Glaskins Perpetual is most reliable. Expect smaller harvests due to heat.
Kauai
Best areas: Kokee and Waimea Canyon. Plant October to March. All varieties perform well at higher elevations. Lower areas need heavy shade.
Frequently Asked Questions
Can I plant rhubarb in Hawaii during summer?
It’s possible but not recommended. Summer heat stresses young plants. If you must plant in summer, choose a very shaded spot and water daily. Expect slower growth and higher failure rates.
How long does rhubarb take to grow in Hawaii?
From planting to first harvest, about 10-12 months. In ideal conditions (cool, shaded, high elevation), you might harvest in 8-9 months. Patience is key – rhubarb is a perennial that improves with age.
Does rhubarb need cold weather in Hawaii?
Not as much as in mainland climates. Rhubarb needs some cool nights (below 65°F) to trigger growth. Hawaii’s higher elevations provide this naturally. At lower elevations, you may get only one harvest per year.
What is the best fertilizer for rhubarb in Hawaii?
A balanced 10-10-10 fertilizer works well. Organic options include composted chicken manure or fish emulsion. Apply every 6 weeks during growing season. Avoid high-nitrogen fertilizers that produce leafy growth.
Can I grow rhubarb from seed in Hawaii?
Yes, but it takes longer. Seeds need 2-3 weeks to germinate at 70°F. Start seeds in pots indoors or in shade. Transplant when seedlings are 4 inches tall. Crowns are faster and more reliable for beginners.
Final Tips For Success
Growing rhubarb in Hawaii is rewarding but requires attention to microclimate. The best time to plant rhubarb in hawaii is during the cooler months, but your specific location matters more than the calendar.
Start with healthy crowns from a reputable source. Prepare your soil well in advance. Provide consistent care and don’t overharvest in the first year. With patience, you’ll enjoy fresh rhubarb from your Hawaiian garden.
Remember that rhubarb is a long-term investment. A well-cared-for plant can produce for 10-15 years. Choose your spot wisely and give it the right start. Your efforts will be rewarded with tart, delicious stalks for pies, jams, and sauces.
If you’re unsure about your elevation or microclimate, ask local gardeners or your extension office. Hawaii has many successful rhubarb growers who are happy to share advice. Learn from their experience to avoid common mistakes.
Finally, don’t be discouraged by initial setbacks. Rhubarb is resilient once established. Even if your first planting struggles, adjust your approach and try again. The unique flavor of homegrown rhubarb is worth the effort.