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onion weed seed

Onion grass (Romulea rosea) has purple flowers, and a bulb and has solid, smaller leaves and is called Onion Weed in some areas.
Three-cornered Garlic (Allium triquetrum) has bulbs, a triangular stem and a strong odour.
Native Leek (Bulbinopsis semibarbata) is a WA native plant and occurs in similar areas. It has yellow flowers with 6 petals and is up to 15 mm diameter. It is readily eaten by stock.
Dune Onion Weed (Trachyandra divaricata) tends to occur near the coast, has white flowers with distinctive yellow stamens and the leaves are strap like and not hollow.

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P31. Photo.

It can re shoot from fragments spread by cultivation.

Round. Hollow. Thin. Hairless. Tip pointed. Seed case often stuck to tip.

Alternate and fairly evenly spaced on the stem. Symmetric, single and more or less upright. On small jointed stalks with a bract at the base. 10-20 mm diameter. Buds pink.
Pistil – 3 carpels.
Ovary – 3 celled, with 2 side by side ovules. Style, thread like and 7 mm long.
Perianth – 2 whorls of 3 segments. Free. Elliptical. Blunt tip
‘Petals’ – 6 pink or white elliptical petals with a brown or purple central stripe. 5-10 mm long.
Stamens – 6. White or cream. Filaments free.
Anthers – Orange

Prefers low fertility sands, gravels and alkaline soils, but occurs on a wide range of soils.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P340. Diagram.

Onion weed has slender, light green strap-like leaves that sprout in clumps and can grow to around knee height. Just like a snowdrop or a daffodil, flower stems appear from the middle of the leaves in spring and early summer producing clusters of pure white drooping flowers that open above the foliage. The flower stems themselves are characteristically three-cornered. The easiest way to confirm that you are looking at onion weed is to crush any part of the plant – it will smell of onions. The good news is that every part of this plant is edible and it can be treated a bit like a spring onion or baby leek.
Onion weed grows from a small parent bulb and spreads underground by producing additional tiny bulbils that grow into dense crowded clumps of foliage. It also spreads rapidly around the garden through seeds cast from pods that form on the three-cornered stems after flowering. Onion weed can form a dense carpet of foliage that suppresses the growth of other plants. It dies back, absorbing nutrients from foliage in autumn down into the bulbs, and then re-grows new foliage in the spring. It is a persistent weed and one that is hard to completely eradicate.
When foliage is pulled out, bulbs and bulbils in the soil below will re-grow. If onion weed is dug up to remove foliage and the parent bulb most often the smaller bulbils – that can be hard to see – get freely distributed through your soil to grow into even more plants.

Controlling onion weed without the use of chemicals takes time and patience. With concerted effort you can certainly make a difference and reduce the quantity present in your soil – however, its likely you’ll have to learn to live with a certain amount of onion weed once it finds its way into your garden.
Remove all foliage whenever you see it. This will weaken plants considerably over time and help to prevent re-growth. The aim is to be even more persistent than onion weed itself and to keep depriving it of its ability to nourish its bulbs hidden in the soil below. Cut foliage with garden shears if you have large clumps. You can even go over it with the lawn mower.
Onion weed can be dug up by hand and bulbs carefully removed from the soil. It is important to dispose of the bulbs in a way the stops them re-entering your garden or compost heap where they will simply re-grow as new plants. Eating them is a fairly sustainable way of disposal. The bulbs can be pickled just like pickling onions. Flowers make an attractive addition to salads and the leaves can be chopped and added to potato salads, soups and stocks or in dishes that require a mild oniony flavour. Whole young plants can be or used just like a spring onion in sandwiches and salads.

Managing Onion Weed

Daiva, you will have to be persistent cutting off any signs of foliage to exhaust the plant, but it is the only way to get rid of it when it is among plants. – Lyn

The reason Gardening Australia advised applying dolomite is because onion weed is more prevalent in soils with an unsuitable pH, and using a poison that is acidic won’t improve the situation. You should test your soil pH annually and make any corrections. When you pull the stem out you loosen the small bulbils, each of which can grow into a new onion weed plant. That’s why it is recommended to cut off the foliage at ground level, rather than pulling it. Maybe sieving the soil is your best option if the problem has multiplied.

Re: onion weed. If I cut it off at ground level , then pour boiling water over it, would that kill it?
Probably not, Rebecca. Perennial weeds like onion grass store nutrients for future growth in their bulbs, and it will probably reshoot. You would have to repeatedly cut it off at ground level as soon as new shoots start to appear or, as it explains in the post, use the black plastic or heavy mulch method.

30 thoughts on “ Onion weed ”

They say the way to remove wandering jew is to move house and not take any plants with you but, seriously, all perennial herbs can be eliminated without herbicides by depriving them of the means to make energy for growth. They all need light to photosynthesise which converts carbon dioxide into glucose for energy. Cutting them off at growth level will deprive them of the ability to grow. With creeping weeds such as convolvulus, wandering jew and kikuyu, this method works very well: Lawn into garden
Chooks love wandering jew. If this weed has become invasive, fencing off the affected area with some chicken wire, and putting chooks in the area for a few days will clear this weed. – Lyn

I seem to have crops of what I call onion weed in my rose garden. They start as tiny very thin shoots that eventually grow to a flat leafed weed about 20cm to 30cm long. They have a bulb and smell like onions and I can’t get rid of them. I haven’t had any flowering, and am generally confused as there seems to be 2 or 3 different weeds that are called “onion weeds”. Certainly mine are not big enough to eat, so how to rid of them?
You are correct Joni – there are several weeds that are commonly called onion weeds, and the best way to get rid of the ones in beds that contain plants is to keeping cutting off the foliage at ground level. If they can’t make carbohydrates, they can’t grow and they can’t produce bulbils. The bulbs will gradually weaken and die off. – Lyn

Hi Irene, glyphosate binds to soil particles until broken down by soil bacteria. It reduces plants’ uptake of Manganese, Zinc, Iron and Boron, which are necessary for disease-resistance. Keep a close watch on your roses for signs of disease, and keep them well-watered so that they are not stressed over summer. An application of organic mulch (kept clear of rose stems) will help soil bacteria to get busy as well as preventing any new growth from the onion weed being able to photosynthesise. – Lyn

This advice is very encouraging re onion weed, so I will start slicing and starving it. But what about the oxalis, wandering jew, convolvulus, kikuyu that are creeping in from neighbouring properties and taking over at least 1/2 of our 2/3 acre block?? Should I just move?