What Types of Weeds Grow in Hawaii



With elevated landscapes and a temperate climate all year round, Hawaii is the perfect place for every homeowner to build their dream garden. But there's one thing that could quickly turn that dream into a nightmare - weeds!



Let's face it; weeds are the enemy of every gardener. Not only do they make your lawn look bad, they also choke the life out of other plants and make the perfect hosts for disease and insects. The first step to tackling weeds is simple: identify them before they start to multiply and take over your garden.



Not sure if what's in your lawn is a weed? Don't fret - here is a list of the types of weeds that grow in Hawaiian lawns and landscapes:



1. Yellow Oleander (Thevetia Peruviana)



Characteristics:

• Small tropical shrubs (2.5 to 3m tall)
• Linear willow-like, glossy green leaves
• Funnel-shaped, fragrant flowers with colors ranging from bright yellow to orange
• Green angular fruits that turn red/black with ripe

As the saying goes, one person's flower is another person's weed.



Don't be fooled by its brightly colored flowers and sweet smell - every part of the yellow oleander is extremely poisonous. They contain cardiac glycosides, particularly thevetin A and B, which inhibits cellular membranes and causes irregular heart activity that may lead to cardiac arrest for both humans and pets.



Yellow oleander grows abundantly across the seasons, as it is resistant to both droughts and cold temperatures. They are commonly found in hedges in most Hawaiian lawns that are nearer to the seaside.



2. Love-vine (Cassytha Filiformis)



Characteristics:

• Perennial, twining vine
• Thick hair-like stems that are yellow, green and sometimes orange (3 to 8m long)
• Leafless
• Tiny white flowers (often used to make lei)
• Fruits are one-seeded drupes that are black when dry

Commonly known as Kauna'oa pehu, the love-vine is one of the most widespread weeds throughout the Hawaiian turf. It is a parasitic vine that climbs over its host plant, usually trees or taller shrubs, and forms dens mats of growth that completely cover the entirety of the host plant. This pathogenic weed squeezes the life out of its host by drawing out its water and nutrients, often killing it.



The love-vine grows primarily in coastal areas and is a common garden problem in most Hawaiian islands, particularly in Kauai, Niihau, Oahu, and Maui.



3. Beggartick (Bidens Pilosa)



Characteristics:

• Flowering herb that grows up to 1.8m tall
• White or yellow daisy-like flowers with black ribbed seeds
• Green, serrated leaves that are oppositely arranged
• Hairy stems with barbed awns

The beggartick is a common weed that belongs to the daisy family (Asteraceae). It is considered highly invasive because of its fast-growing nature - a single plant can produce up to 6000 seeds that can easily overpopulate your lawn in just a matter of days.



The beggartick's dry fruit are covered with spikes that can injure flesh and can easily get stuck on clothes and fur - proving to be a quite a nuisance for both humans and pets.



This perennial herb thrives in temperate climates like Hawaii, but they usually bloom more abundantly in summer and autumn. The flowers are usually white, although a yellow variety can commonly be found in Koko Crater BG, Oahu.



4. Pepperweed (Lepidium Virginicum)



Characteristics:

• Glossy, dark green leaves
• Stems grow up to 4 ft tall
• Enlarged roots at the surface of the soil
• Racemes with small, white densely-clustered flowers and greenish fruits

As its name suggests, pepperweed is an edible plant known for its peppery taste. Its young seeds are used in some cultures for seasoning, as an alternative to black pepper.



What makes pepperweed a noxious species is its extensive creeping root system that can be difficult to control. The roots can grow as deep as 9ft into the soil and absorb water and nutrients from nearby plants, effectively displacing them and changing soil conditions in your lawn.



Pepperweed typically grow in coastal areas, though they have extended their reach inland and can commonly be seen along highway roads.



5. Chinese Violet (Asystasia Gangetica)



Characteristics:

• Herbaceous spreading herb that grows up to 1m high, but can cover other plants up to 3m
• Oval-shaped opposite leaves
• White, bell-shaped flowers with purple markings on the lower lip
• Green, guitar-shaped fruit capsules that turn brown when opened

Traditionally used as an herbal remedy, the Chinese violet is considered a noxious weed for one reason - it's a perennial creeper. It spreads like a vine throughout the surface of the soil and forms a dense ground cover over large portions of your lawn. This cover stretches over nearby plants, smothering them and depriving them of water and nutrients.



The Chinese violet can survive practically anywhere. It tolerates a wide range of soil types, but thrives mostly in the coastal, sandy soils of Hawaii. Its flowers are mostly white with a lavender hue, although darker purple varieties were discovered in Kalepolepo, Maui.



6. Wedelia (Sphagneticola Trilobata)



Characteristics:

• Low-climbing plant with hairy stems with rooting at the joints (up to 30cm in height)
• Serrated, hairy, lobed leaves that vary from light to dark green
• Bright yellow daisy-like flowers

The Wedelia may look like just any other subspecies of daisy, but it is in fact included in the IUCN's list of the world's top 100 worst invasive alien species. It spreads vegetatively through roots in the stems, rather than by seeds.



Much like the Chinese violet, this invasive weed crawls throughout your lawn creating a dense ground cover over nearby plants and can even climb trees up to a short distance. This prevents other plants from growing and regenerating effectively. It can propagate faster than other groundcovers, and may even spread out to neighboring lawns and road sides if not eliminated at first sight.



Wedelias grow abundantly in sunny climates and lowlands with moist soil.



7. Sleeping Grass (Mimosa Pudica)



Characteristics:

• Prickly, low-growing shrub that grows up to 1m tall
• Prickly, leaves that grow in pairs and are extremely sensitive to touch
• Pale pink or purple flower heads
• Long fruits containing pods

If you grew up along the lowlands of Hawaii, then you'll probably remember playing with these unique plants once or twice during your childhood.



Sleeping grass, fondly called zombie grass and touch-me-not plant, is known for its rapid leaf movement - it responds to touch and other stimuli by quickly closing its leaves and drooping. This is called seismonastic movement and is used as the plant's defense mechanism against predators like spiders.



Despite its playful appearance, sleeping grass is an extremely invasive weed. It forms a dense ground cover across your lawn that can drastically change the physic-chemical properties of the soil where it grows. In extremely high summer temperatures, sleeping grass can be a fire hazard when growing near thick bushes. Some varieties native to Hawaii have also been found to be toxic to some animals.

While some parts of the world can be a little casual with their lawn watering schedule-or even just leave it to nature; Hawaii lawn care is a little more involved.

In a warm climate like this, you need to put some real thought into what time and how often you water your lawn.

You might be surprised to learn just how many factors play a role in when the ideal watering time is.

The short answer to night-time watering is yes, you should water your lawn at night. But it's not what you might be thinking when we say that.

Read on, and we'll break down exactly why night-time is the best time for a bit of Hawaii landscaping.

When Should I Water My Lawn?

"Night-time" is a bit vague, we get it.

There's a lot of hours during the night, and the conditions can be quite different depending on which of those hours you choose.

The best time to water your lawn is a couple of hours before sunrise.

Anytime during the day will likely result in the water evaporating far too quickly.

On the other hand, watering in the late evening can leave the grass wet for too long, which may lead to bacterial and fungal growth.

Watering a little before the sun comes up will give your lawn enough time to absorb the water before the heat of the day evaporates the excess.

This should reduce the chances of anything unwanted springing up in your garden.

Other Factors That Make Night-Watering Better

Another thing to consider when watering your lawn is wind.

It is often less windy in the dark of early mornings as the colder night air settles, and before the heat of the day starts stirring things up.

This makes it much easier to get an even distribution of water on your lawn and avoid patchiness.

Perhaps the least intuitive reason to water your lawn at night is the water pressure.

Any water delivery system has a limit to what it can deliver at one time.

The more people using water at once, the lower the pressure will be coming out of your faucets.

One thing you can be sure of in the early hours of the morning is that there won't be many people up and about.

Contrast this with a few hours later when people are getting ready for work, taking showers and making coffee.

Conclusion

We can't all be Hawaii lawn and landscape experts.

Still, with a little consideration into how and when you water your garden, you could have a lawn that looks like it was maintained by an expert.

Of course, these are not absolute rules; remember, some water is better than none.

​If your sprinkler breaks down, or you sleep through your alarm, it's better to water your lawn under the blazing heat of a windy afternoon with weak water pressure than to not water it at all.