Hawaii’s tropical environment allows nutgrass and wedelia to overtake grass areas within weeks of planting. Understanding the types of lawn weeds in Hawaii is the first step to keeping your yard healthy and green. The islands’ warm, wet climate creates perfect conditions for a wide variety of invasive plants that can quickly ruin a manicured lawn.
You might notice some weeds popping up even after you’ve put in new sod or seed. That’s because Hawaii’s year-round growing season gives weeds a constant advantage. But don’t worry—once you know what you’re dealing with, you can take action.
This guide covers the most common weeds you’ll find in Hawaiian lawns, how to identify them, and what to do about them. We’ll look at broadleaf weeds, grassy weeds, and sedges, plus some invasive species that are particularly troublesome in the islands.
Common Broadleaf Weeds In Hawaii Lawns
Broadleaf weeds are easy to spot because their leaves are wide and flat, unlike grass blades. They often have showy flowers and can spread quickly through seeds or runners.
Wedelia (Sphagneticola Trilobata)
Wedelia is one of the most aggressive weeds in Hawaii. It’s a creeping plant with yellow, daisy-like flowers. It forms a dense mat that smothers grass and other plants. You’ll often see it in shady, moist areas of the lawn.
- Leaves are glossy, dark green, and slightly toothed
- Flowers are bright yellow, about an inch wide
- Stems root at the nodes, making it hard to pull out
- Grows year-round in Hawaii’s climate
Wedelia spreads through stem fragments and seeds. Even a small piece left behind can regrow. Hand pulling is difficult because the stems break easily. You’ll need to dig out the roots completely or use a selective herbicide.
Chickweed (Stellaria Media)
Chickweed is a low-growing weed with small, oval leaves and tiny white flowers. It thrives in cool, damp conditions, which you might find in higher elevation areas like upcountry Maui or the Big Island’s volcano region.
This weed forms dense patches that can choke out grass. It spreads quickly through seeds and stem fragments. Chickweed is annual in most places but can be perennial in Hawaii’s mild climate.
- Leaves are opposite, smooth, and pointed
- Flowers have five deeply notched petals
- Stems have a single line of hairs
- Prefers shaded, moist soil
To control chickweed, improve drainage and reduce shade. Mow regularly to prevent seed production. Pre-emergent herbicides applied in fall can help prevent germination.
Dollarweed (Hydrocotyle Umbellata)
Dollarweed looks like a miniature lily pad. It has round, scalloped leaves that grow from a central stem. It’s common in wet, poorly drained areas of lawns. Dollarweed spreads through seeds and underground runners called rhizomes.
This weed is particularly troublesome in lawns with irrigation issues. If you see dollarweed, it’s a sign your soil stays too wet. Fixing drainage problems is the best long-term solution.
- Leaves are round, about 1-2 inches wide
- Leaves have a central stem attached to the underside
- Small white or greenish flowers appear in clusters
- Grows in standing water or saturated soil
Herbicides containing 2,4-D or dicamba can control dollarweed. But you must also address the moisture problem or it will return. Aerating the soil and reducing irrigation frequency helps.
Creeping Oxalis (Oxalis Corniculata)
Creeping oxalis is a low-growing weed with clover-like leaves and small yellow flowers. It spreads by seeds and creeping stems that root at the nodes. This weed is common in lawns throughout Hawaii, especially in areas with thin grass.
Oxalis produces seed pods that explode when touched, scattering seeds several feet away. This makes it hard to control once established. It also has a taproot that makes hand pulling difficult.
- Leaves are heart-shaped, in groups of three
- Flowers are bright yellow with five petals
- Seed pods are cylindrical and pointed
- Grows in full sun to partial shade
Pre-emergent herbicides can prevent oxalis seeds from germinating. For existing plants, spot-treat with a broadleaf herbicide. Maintaining a thick, healthy lawn is the best prevention.
Grassy Weeds Common In Hawaii
Grassy weeds look like grass but grow faster and coarser. They blend in with your lawn until they form unsightly clumps. These weeds are particularly hard to control because they’re similar to desirable grass species.
Crabgrass (Digitaria Spp.)
Crabgrass is a summer annual that germinates in warm soil. It grows in low, spreading clumps with wide leaf blades. In Hawaii, crabgrass can germinate year-round because soil temperatures stay warm enough.
This weed is opportunistic. It fills in bare spots in the lawn where grass is thin. Once established, it produces thousands of seeds that can remain viable in soil for years.
- Leaf blades are wide, about 1/4 to 1/2 inch
- Stems grow outward from the center, like crab legs
- Seed heads are finger-like spikes
- Grows in compacted soil and full sun
Pre-emergent herbicides applied in early spring are effective against crabgrass. But you must time the application before soil temperatures reach 55°F. In Hawaii, that can happen any time of year, so watch for consistent warm weather.
Goosegrass (Eleusine Indica)
Goosegrass looks similar to crabgrass but has a distinctive white or silver center. It forms flat, circular patches in compacted soil. Goosegrass is common along walkways, driveways, and in high-traffic areas of the lawn.
This weed is more tolerant of drought and compaction than crabgrass. It’s often a sign that your soil needs aeration. Goosegrass roots are tough and fibrous, making hand pulling difficult.
- Leaf blades are folded in the bud
- Stems are flattened at the base
- Seed heads have 2-5 spikes arranged like a finger
- Grows in hard, compacted soil
Control goosegrass by aerating the soil to reduce compaction. Pre-emergent herbicides can help, but they must be applied before germination. Post-emergent herbicides work best on young plants.
Torpedograss (Panicum Repens)
Torpedograss is one of the most invasive grassy weeds in Hawaii. It gets its name from the sharp, pointed rhizomes that can pierce through landscape fabric and even asphalt. This weed spreads aggressively underground and is extremely hard to eradicate.
Torpedograss thrives in wet areas but can survive in dry conditions too. It’s common in lawns near drainage ditches, ponds, or irrigated areas. Once established, it can take over an entire lawn within months.
- Leaf blades are stiff, pointed, and bluish-green
- Rhizomes are white, thick, and sharp
- Grows 1-3 feet tall if unmowed
- Prefers moist, sandy soil
Controling torpedograss requires persistence. Hand pulling rarely works because rhizomes break off and regrow. Systemic herbicides like glyphosate can help, but multiple applications are needed. In severe cases, you may need to remove the entire lawn and start over.
Bermudagrass (Cynodon Dactylon)
Bermudagrass is both a desirable lawn grass and a troublesome weed, depending on where it grows. In Hawaii, it’s often used for lawns because it’s drought-tolerant and spreads quickly. But when it invades flower beds or other grass types, it becomes a weed.
This grass spreads through seeds, stolons (above-ground runners), and rhizomes. It’s aggressive and can choke out other plants. Bermudagrass is particularly problematic in lawns planted with St. Augustine or centipedegrass.
- Leaf blades are fine-textured and gray-green
- Stolons run along the soil surface
- Seed heads have 3-7 finger-like spikes
- Grows in full sun and tolerates heat
To control Bermudagrass in flower beds, use a grass-specific herbicide. In lawns, you can manage it with regular mowing and fertilization. But if it’s invading a different grass type, you may need to spot-treat or remove it manually.
Sedges And Grass-Like Weeds
Sedges look like grass but have triangular stems and grow in wet areas. They’re common in Hawaii lawns with poor drainage or overwatering. Sedges are harder to control than grasses because many herbicides don’t affect them.
Nutgrass (Cyperus Rotundus)
Nutgrass is probably the most hated weed in Hawaii lawns. It’s not actually a grass but a sedge. It has triangular stems and produces underground tubers called nuts. These nuts can remain dormant in soil for years and regrow when conditions are right.
Nutgrass spreads through nuts, rhizomes, and seeds. It thrives in wet, poorly drained soil. Once established, it’s extremely difficult to eradicate. Hand pulling often makes it worse by spreading the nuts around.
- Stems are triangular in cross-section
- Leaves are dark green and shiny
- Produces purple-brown flower heads
- Underground nuts are hard and brown
Controling nutgrass requires patience. Use a sedge-specific herbicide like halosulfuron or sulfentrazone. Apply when the plant is actively growing. You’ll need multiple applications over several months. Improving drainage and reducing irrigation can help prevent regrowth.
Kyllinga (Kyllinga Brevifolia)
Kyllinga is another sedge that looks similar to nutgrass but is smaller. It forms dense, low-growing patches in wet areas of the lawn. Kyllinga spreads through seeds and rhizomes and can quickly cover large areas.
This weed is common in lawns with poor drainage or overwatering. It’s often mistaken for nutgrass but doesn’t produce the same large tubers. Kyllinga is easier to control than nutgrass but still requires specific herbicides.
- Stems are triangular but smaller than nutgrass
- Leaves are bright green and fine-textured
- Flower heads are round, white or green
- Grows in wet, compacted soil
Kyllinga can be controlled with the same herbicides used for nutgrass. Improving drainage and reducing irrigation frequency will help prevent it from returning. Regular mowing can also reduce seed production.
Invasive Weeds To Watch For
Some weeds in Hawaii are classified as invasive species because they spread rapidly and harm native ecosystems. These weeds can be particularly aggressive in lawns and gardens.
Fireweed (Senecio Madagascariensis)
Fireweed is a fast-growing shrub that produces yellow flowers. It’s invasive in Hawaii and can take over pastures and lawns. Fireweed is toxic to livestock and can cause liver damage if eaten.
This weed spreads through seeds that are carried by wind. It can grow up to 6 feet tall if not controlled. Fireweed is common in disturbed areas, roadsides, and overgrazed pastures.
- Leaves are narrow, dark green, and slightly hairy
- Flowers are yellow, daisy-like
- Stems are woody at the base
- Grows in full sun and poor soil
Control fireweed by pulling young plants before they flower. Herbicides containing triclopyr or glyphosate can be used on larger plants. Mowing regularly can prevent seed production.
Hilo Grass (Paspalum Conjugatum)
Hilo grass is a creeping grass that forms dense mats in shady, moist areas. It’s common in lawns throughout Hawaii, especially under trees. Hilo grass spreads through stolons and seeds and can quickly cover large areas.
This weed is difficult to control because it thrives in conditions where other grasses struggle. It’s often found in lawns with poor drainage or low light. Hilo grass can crowd out desirable grass species over time.
- Leaf blades are broad and dark green
- Stolons root at the nodes
- Seed heads are two-branched spikes
- Grows in shade and wet soil
To control Hilo grass, improve light penetration by pruning trees. Reduce irrigation to dry out the soil. Herbicides containing quinclorac can be effective, but multiple applications may be needed.
Prevention And Control Strategies
The best way to deal with lawn weeds is to prevent them from establishing in the first place. A healthy, thick lawn is your best defense against weeds. Here are some strategies to keep your Hawaii lawn weed-free.
Maintain Proper Mowing Height
Mowing too short stresses grass and allows weeds to take over. Most Hawaii lawn grasses should be mowed at 2-3 inches tall. Taller grass shades the soil, preventing weed seeds from germinating.
- Set your mower blade to the highest recommended height for your grass type
- Mow regularly, but never remove more than one-third of the leaf blade at once
- Keep mower blades sharp to avoid tearing grass
- Leave grass clippings on the lawn to return nutrients to the soil
Water Deeply And Infrequently
Frequent, shallow watering encourages weed seeds to germinate. Instead, water deeply but less often. This encourages grass roots to grow deeper, making the lawn more drought-tolerant and competitive against weeds.
- Water 1-1.5 inches per week, including rainfall
- Water in the early morning to reduce evaporation
- Avoid watering at night, which promotes disease
- Use a rain gauge to measure how much water your lawn receives
Fertilize Appropriately
Weeds thrive in poor soil where grass struggles. Regular fertilization helps grass grow thick and compete with weeds. But too much fertilizer can also encourage weeds, so follow recommended rates.
- Use a slow-release fertilizer with a balanced N-P-K ratio
- Apply fertilizer during the growing season, typically spring and summer
- Follow soil test recommendations for specific nutrient needs
- Avoid over-fertilizing, which can lead to thatch buildup
Use Pre-Emergent Herbicides
Pre-emergent herbicides prevent weed seeds from germinating. They’re most effective against annual weeds like crabgrass and goosegrass. Apply them before the weed seeds start to grow.
- Apply pre-emergent in early spring and again in fall
- Water the herbicide into the soil after application
- Don’t disturb the soil after applying, or you’ll break the barrier
- Use products containing prodiamine, dithiopyr, or pendimethalin
Frequently Asked Questions
What Is The Most Common Weed In Hawaii Lawns?
Nutgrass (purple nutsedge) is one of the most common and frustrating weeds in Hawaii lawns. It thrives in the islands’ warm, wet climate and is difficult to control because of its underground tubers.
How Do I Identify Weeds In My Hawaii Lawn?
Look at the leaf shape, growth habit, and flower type. Broadleaf weeds have wide leaves, grassy weeds look like coarse grass, and sedges have triangular stems. Compare your weeds to pictures online or take a sample to your local garden center.
Can I Use Vinegar To Kill Lawn Weeds In Hawaii?
Household vinegar is not effective on most lawn weeds. Horticultural vinegar (20% acetic acid) can kill young weeds but will also damage grass. It’s best used for spot-treating weeds in driveways or patios, not in lawns.
When Is The Best Time To Apply Herbicide In Hawaii?
Because Hawaii has a year-round growing season, you can apply herbicides any time weeds are actively growing. However, early morning or late afternoon applications are best to avoid heat stress on the grass. Avoid applying before rain.
How Do I Prevent Weeds From Coming Back?
Maintain a thick, healthy lawn through proper mowing, watering, and fertilization. Fill in bare spots with grass seed or sod. Use pre-emergent herbicides at the right times. And address underlying issues like poor drainage or soil compaction.
Dealing with lawn weeds in Hawaii can feel like a constant battle. But with the right knowledge and consistent care, you can keep your lawn looking its best. Start by identifying the weeds you have, then choose the most effective control method for each type.
Remember that prevention is always easier than cure. A healthy lawn is your best defense against weeds