What Are Annual Weeds?

A weed is loosely defined as any plant growing in the wrong place, which largely depends on your location and personal preferences. The exception is a range of highly invasive or noxious weeds that are banned in various states.

Annual weeds are generally easier to eradicate than perennial weeds, which often develop strong, thick tap roots and woody stems as they mature.

Here’s a list of common Annual Grassy Weeds to look out for:

• Barley Grass – An annual species renowned for rapidly germinating after autumn rain, it grows to 45cm, has light green leaves that are often twisted, and produces hard seed heads.
• Barnyard grass – A tufted annual grass with flat, light green leaf blades up to 30cm long. Flower spikes at the tip of the stalk are green or purple and each plant can produce more than 40,000 seeds.
• Crabgrass – Also known as Summer Grass, it looks like grass but has a wide leaf blade and sends out tough stems with fingers of seed heads at the tips.
• Crows Foot Grass – A tufted short-lived grass with spreading or semi-upright stems up to 60cm long and narrow leaf blades. Seed heads can have up to 10 spikelets on each stem.
• Ryegrass – Annual ryegrass is an upright clumping grass with dark green glossy leaves tinged purple at the base. Flowering stems produce flat spikes in winter and early spring and numerous seeds which are quick to germinate after rain.
• Wild Oats – An erect cool season annual grass with open branched nodding clusters of spikelets. Mature seeds are notorious for burrowing into the ears and skin of pets and causing abscesses.
• Winter Grass – Most prevalent in winter and spring, it has a bright green leaf that is very soft when young and difficult to mow. It develops into clumps and the invasive roots will choke out your lawn.

Common Broadleaf Weeds to look out for include:

• Burr Weed – A creeping weed that germinates in autumn and winter, it has serrated heart-shaped leaves divided into three. Stems are long and reddish, and the clustered flowers are small yellow and pea shaped. Pods produce prickly burrs that dry out and spread seeds.
• Cape Weed – A low-growing herbaceous annual, it starts as a rosette of deeply lobed leaves with whitish undersides. The daisy-like flowers have pale yellow petals and dark purplish centres made up of tiny tubular flowers.
• Carrot Weed – Also known as Batchelor’s Button or annual Buttonweed, it grows in a thin mat with spindly stems and produces yellow or white button-like flower heads with no petals.
• Chickweed – It has soft hairy stems and small oval leaves paired along the stems. Plants can produce tiny white flowers as soon as 4-5 weeks after germination. 
• Clover – Distinguished by its trifoliate leaves and creeping stems that put down roots where they touch the ground, it germinates in winter. Flowers are white or pink and plants drop numerous tiny seeds before dying off in the summer heat.
• Cudweed – Rosettes of glossy grey-green, serrated-edged leaves, plants put up a stem in spring and produce small flowerheads containing many tiny flowers, and woolly seed heads.
• Fleabane – The rosette soon develops hairy upright branched stems. Lower leaves are bluntly toothed, and the smaller upper leaves are narrower and more finely toothed. The flower heads turn white and puffy as they mature.
• Marshmallow –A semi-upright weed with a very deep tap root, it has rounded leaves with seven lobes, produces small mauve, pink row white flowers and reproduces by seed that can persist for up to 100 years. It can be poisonous to animals.
• Thistles – Herbaceous annual weeds that have spiky leaves and stems and mostly purple flowers.

Staying a step ahead of weeds by controlling them when plants are small is essential for ensuring the good health of your lawn.

It’s possible to safely manage Annual Weeds using chemical or natural methods, or a combination of the two.

The primary objective is to stop these plants setting seed for the next year or prevent last year’s seeds from growing into new plants.

Using a Herbicide

In areas with a known Annual Weed problem, pre-emergent herbicides containing the active ingredients Prodiamine or Oxadiazon can be useful for stopping newly germinated seeds in their tracks.

You can read our guide to Using pre-emergent herbicides here.

Broadleaf Weeds are usually easier to identify than grass weeds and there’s a wider range of options, including selective and broad spectrum herbicides.

Always check the product label to make sure it is effective on the weed you’re trying to control and safe for use on the type of grass in your lawn. Buffalo lawns are especially sensitive to some herbicides.

OxaFert 16-2-6 20kg

Indigo Halo-Force 750WG 25gm

Bow and Arrow 500mL

Barricade 1L

The best time to apply post-emergent herbicides is when weeds are small and actively growing so they readily absorb the active ingredient/s through their leaves.

In the case of Summer Broadleaf Weeds, this will be spring, or autumn for winter Broadleaf Weeds.

Pre-emergent herbicides should be applied before weed seeds germinate, which is usually in early spring.

Some herbicides will need to be watered in, while others have a period

There’s more information about correctly applying herbicides here.

How Long do Weed Killers Take to Work?

The speed at which grass weeds die after herbicide application can depend on several factors, including the type of herbicide used, weed maturity, the size of the infestation, and the health of your lawn.

If applied correctly, you will start to see the effects of some weed killers within 48 hours of spraying, while others might take 2-3 weeks.

The weeds may take longer to die off completely and may require repeat applications 6-8 weeks later for large, persistent weed infestations.

There will be times when manual removal of weeds is the best, cheapest or safest method of control.

Annual Weeds often have shallow roots and can easily be pulled out by hand or chipped out with a hoe.

When weeds are small or there’s only a few of them, it makes more sense to pull them up by hand than going to the trouble of mixing and spraying a batch of herbicide then properly disposing of the leftover mixture.

Other scenarios when manual removal works best includes new lawns, which are more vulnerable to chemical damage than established lawns, and when weeds are growing in Soft Leaf Buffalo lawns which are more sensitive to herbicides than most other grasses.

You can read our complete guide to pulling weeds from your lawn here.