Warmer weather can help with growing our gardens – but it can also mean a tricky time for pesky weeds. Discover the 5 weeds to watch for in summer, plus the best way to tackle them.
You might be inspired by the longer and warmer days to get into your garden, or even volunteer in your local park or reserve – but it’s more-so the weeds that really need your attention.
There are lots of weeds that thrive in hotter conditions as they grow more seeds and spread more easily.
Luckily we’ve got you covered – here are 5 weeds to watch for this summer and what to do about them.
1. Khaki
If we get some summer rain you may not have to look too hard to spy spiteful khaki weed (Alternanthera pungens).
Khaki is a small, thick weed that covers the ground, often spreading into a dense mat. It has reddish stems and green, oval-shaped leaves. The pale yellow to green spikey burrs are about 1 cm long and can remain in the ground for many years.
Khaki has a central main root, called a taproot, which helps this weed store energy over time. This means even if you have removed the leaves and think the plant is gone, the taproot can have enough energy for the plant to come back again and again.
Also, the burr of this plant, or the small, spikey, seed covering, makes it easy for this weed to spread because spikey hooks tangle in clothing, footwear, animal fur, or even tyres, and can then be moved to new locations.
Khaki is a notifiable weed, meaning you should tell us if you see it, as it is one which we are working hard to get rid of in the metropolitan area.
You can remove khaki by pulling up individual plants, however care needs to be taken to ensure that the main tap root of the plant, plus any remaining burrs, are also collected and removed.
For chemical control advice, check out information from the PIRSA website.
2. Silverleaf nightshade
Silverleaf nightshade (Solanum elaeagnifolium) is a declared weed, so there is a requirement to control it if it’s growing on your property.
It thrives in summer because of its deep root system. This system grows up to 2 m below ground to access water from deep in the soil.
Silverleaf nightshade is a predominantly green plant with purple flowers and small green to yellow fruits.
It grows 30 to 60 cm high, with green branches covered with short, tan-coloured prickles.
Silverleaf nightshade may be confused with native plants such as quena (Solanum esuriale) or western nightshade (Solanum coactiliferum). Make sure you know whether you’ve got the weed or the native before removing it. If you’re unsure, you can upload a photo to iNaturalist, an app and web-based platform, which can help with plant species ID.
Once established, silverleaf nightshade can be difficult to control so keep an eye out for silverleaf nightshade plants, and manually removing them as quickly as you can.
For effective control of lots of plants, you might opt for chemical control. Ideally this requires 2 to 3 treatments over the growing season, applied at the early stage of flowering but before the plant has berries.
For more information on chemical control, check out information from PIRSA. Slashing plants can reduce the number of times you’ll need to do chemical treatments.
3. Coolatai
Coolatai (Hyparrhenia hirta) is a highly invasive grass.
It is a thatching grass, meaning you’ll see it growing in tight clumps, which can grow up to 1.5 m high and wide. It has thin grey to green leaves, and spikey grey to white flowers that grow in pairs and form a ‘V’ shape toward the end of their stalks.
The dense clumps of coolatai grass prevent native species from growing because of the space they take up – ultimately altering habitats and impacting on our native wildlife.
Coolatai can look very similar to the native kangaroo grass (Themeda triandra). To tell the difference, have a close look at the flower heads, as kangaroo grass will form a compact cluster of little spikelets rather than the V-shape of the seed heads of coolatai flowers.
It can also look a little like native lemon-scented grass (Cymbopogon ambiguous). If you are unsure which species it is, wait until you can see seedheads as that might help you identify it easier, or post pictures to the iNaturalist app to get help.
Coolatai is both a declared weed and a notifiable weed, which means landowners should tell us about sightings of this plant, as well as controlling it on their property.
It can be removed by hand where there is a small number of plants. If its seed heads are present, it is best to ensure they are bagged before being placed in your household bin to prevent further spread.
For advice on chemical control, check out the information from PIRSA.
4. Buffel grass
Buffel grass (Cenchrus ciliaris and C. pennisetiformis) is one to keep an eye out for as it is a drought-resistant weed – so even if we get a hot, dry summer this pest plant can still spread.
It has bright green leaves with a visible vein down the centre, however these will dry to a yellow or straw-coloured clump when the plant is dormant, or not growing.
It has a fluffy white or purple seed head that can produce seeds through the year, but it’s more common to see them from November through until May, and after rain.
Buffel grass is a declared weed and notifiable weed, meaning you should tell us if you see it, as it is one that we are working hard to get rid of in the metropolitan area.
While individual plants can be dug out of the ground to prevent spread, larger groups of this weedy grass may need targeted chemical control. You’ll need to revisit the weedy area several times over summer and even in the coming years to make sure this weed doesn’t come back.
For advice on chemical control, check out the information from PIRSA.
5. Blackberry
Tasty as the fruits are – blackberry (Rubus fruticosus aggregate) is a declared weed – which means you need to control it on your land.
There are a number of pretty similar plant species, 16 in fact, that make up blackberry. All of which are weedy. There is however also a thornless cultivar of blackberry that is okay to grow.
Blackberry is a long-lived and fast-growing shrub, which forms in spiny twining branches that can grow up to 7 m long. It has dark green leaves with a lighter underside, and its leaf veins and stalks are covered in spikes. It has white or pink flowers, and will fruit from late spring and throughout summer, with berries that start off green, go to red, and eventually ripen to black.
It’s the seeds from the blackberry fruit itself – each fruit can have about 80 seeds – that help this weed spread. Animals that eat the berries and when they poop them out, this contributes to the seeds ending up travelling far and wide. The thick and dense way that blackberry grows can crowd out native plants, and its spiny stalks can even cause harm to wildlife.
There is a native raspberry (Rubus parvifolius) that looks very similar to weedy blackberry, so make sure your identification is correct before undertaking control. Native raspberry has more pronounced and deep veins on its leaves and very pink flowers. If you’re not sure, take some photos and upload them to the iNaturalist app for assistance with identification.
In some cases, blackberry plants can provide shelter to southern brown bandicoots, so if you are in an area that has bandicoots it is best to be aware of this before undertaking any control. If you are not sure, contact us or check out these bandicoot habitat management guidelines.
If you don’t want to get rid of this weed altogether, you can reduce the size of the plant through cutting it back. This won’t kill the plant, but can stop it from spreading. For advice on chemical control, check out the information from PIRSA.
Wanna learn more about weeds?
Learn about Adelaide’s problem weed fountain grass, or get the information you need to know on Adelaide’s weeds.