Onion weed

Onion weed (Nothoscordum inodorum) seems to cause problems for quite a few gardeners who are unsure about organic ways to be rid of this pest. I did cover onion weed previuosly in a post on perennial weeds but, as it is a common problem, it might be worth covering it separately.
It is fairly easy to eradicate it from lawns, by keeping grass growing vigorously. Healthy lawn grass will out-compete onion weed in a fairly short time and no other treatment is necessary. In fact, onion weed in lawns is merely a sign that your lawn needs a bit more TLC.
Onion weed in garden areas is an entirely different problem. Because onion weed is a perennial weed, it stores nutrients and carbohydrates in its bulbs to generate growth in the following season, in the same way as spring bulbs such as daffodils. Trying to pull out or dig up these weeds in garden areas results in the parent bulbs releasing tiny bulbs (bulbils) from the base of the main bulb. These grow into mature plants, and all the digging has achieved is multiplication of the problem.
To get rid of onion weed, you have to prevent the bulbs storing food for growth. Onion weed can also produce seed. Cutting off the foliage at ground level will prevent the plants making carbohydrates in their leaves, and also prevent seed forming.
In an unused garden area, you can do this by slashing, or mowing, the foliage to ground level, then covering the area with black plastic for several months. Anchor the edges of the plastic with planks, bricks or whatever you have to prevent it blowing away. Deprived of moisture and the sunlight that enables it to store carbon dioxide as carbohydrates (photosynthesis), the bulbs will weaken and die. Avoid using clear or light plastic, as these will still allow the plants to photosynthesize and, in some conditions, they can actually improve weed growth.
In garden beds that are being used, onion weed is more difficult to eradicate because the bulbils can be released whenever you disturb the soil. Cut off the foliage at ground level with shears to prevent it making food for the bulbs. Then mulch the beds with 5–7 cm of mulch. You may have to cut back foliage several times as soon as it appears. If you do this consistently, bulb growth will become progressively weaker, and you will eliminate the problem without disturbing the soil and stimulating the growth of more bulbs.
When you have a chance to leave a particular bed lying fallow, you can give the bed the black plastic treatment. Onion weed is more commonly found in undernourished soils, or where soil pH is unsuitable for healthy plant growth. Where onion weed has been a problem, check your soil pH, and improve organic matter content in soil to prevent the problem recurring.

30 thoughts on “Onion weed

  1. Hi there, Thank you for your help with these weeds… they’re enough to send you crazy!
    I have an onion weed problem in a section of roses, an area about 2m x 2m. Not knowing better, i have been trying to carefully dig them up over the last 8 months or so. Only to find they keep appearing and more prolific.
    If I cut them off at ground level and keep doing this, does it stop the little bulb from turning into a cluster? If this is the case, if I just keep cutting as they come up, will they eventually become less and less?
    This sure seems easier than digging and carefully sifting through the dirt.
    Would you mulch after the first few trims or wait until their growth starts to slow down? Currently it’s obviously their fertile season as they’re shooting up everywhere. Thank you kindly

    Yes, Sophia, trying to dig out onion weed will drive you crazy as it only increases the spread of this pest. The reason cutting off growth as it appears is the way to get rid of perennial weeds, such as Onion Weed, is simple. In order to grow, plants need to convert carbon dioxide from the air into carbohydrates, and they do this in daylight through the green cells in their leaves in a process called ‘photosynthesis’. By removing the parts that photosynthesise, you prevent them from making further growth. However, as Onion Weed is a perennial, and able to store carbohydrates in the bulbs below ground, you will need to remove the above ground growth several times until the bulbs exhaust their stored carbohydrates. Immediately after cutting off the growth, it helps to thickly mulch the soil surface, but keep the mulch at least a hand width from your roses’ main stem. – Lyn

  2. Have just starting using jet nozzle of steam cleaner into centre of onion weed plants at ground level until leaves wilt. After 4 days, dieback is progressing really well.

    1. Yes, but you need to di it repeatedly, AND be careful not to split the tiny bulbs from the major one. I seemed to have thing coming undef control, but a month away and no treatment, they have come back thicker than ever. Much easier to cut back the leaves – will try that now 🙂

  3. Can you destroy onion weed by burning with a flame
    Geoff, although you can kill a variety of weeds with flame-weeding, applying it to onion grass would be no more effective than cutting off the foliage at ground level. The nutrients it needs for growth are in the bulb and bulbils under the soil. It’s easy to get rid of it in lawns by improving watering and fertilising of the grass, which will out-compete the weed growth. It is harder to get rid of in beds because any disturbance of the soil just spreads the bulbils.

  4. Some great advice thanks. Front garden is full of onion weed, again. We used black plastic for about 3 years as the onion weed was so bad. It helped, I only had to keep picking the leaves out around the edges and around the roses. If you get right down to the base of the leaves and pull gently the white stem comes out completely just leaving the bulb. And for a couple of years there was minimal growth even after the plastic came off. Now I have soil and hardwood mulch with about 6 roses along the bed and a wall of sweet peas along the wire front fence. The onion weed has gone berserk!
    I definitely need to replenish the bed with compost and other goodies and add some dolomite lime (Gardening Australia tip last week for onion weed) but I am close to digging the whole thing up and sieving it or ditching it. Poison does work, it has an acid in it as well, if I cut the leaves across the middle and paint the cut stem and centre but it isn’t stopping the bulbs and I hate using it. Maybe an option is to put plastic down again, and raise a new garden bed on top of it? Getting old, I can’t keep bending over to pull the onion weed! Thanks for the good advice

    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.

  5. Should it be put in compost or not?
    Cut off foliage without seed heads would be ok in compost, but not the bulbs. They would just spread the problem.

  6. 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.

  7. I have been spraying a section of ground every few weeks (as soon as I see any new growth) with glyphosate for the past 3 YEARS yet after a few weeks I see new small growth so spray again.
    I do not allow the new growth to get any taller than around 3cm and so the leaves are very thin and small. I NEVER allow it to go to seed.
    In another section I have resorted to carefully digging it out and that is having a noticable effect.
    Based on that I don’t think that glyphosate is effective regardless of what the claim.

  8. I struggled with onion weed for many years – making the problem worse – in a large garden in Perth. Now we are in Melbourne and a few years ago I dug over a section of the nature strip with the result that I disturbed the bulblets (didn’t know they were there) and now I have a massive onion weed problem in that area. I dug out some of them and put the bulbs in a bucket full of water to be left for three weeks to make onion tea, as I’ve read that if you pour this on the active plants it will kill them… any thoughts on this? Additionally I go out every day with kitchen scissors and cut them off at ground level – am astonished at how quickly they can grow. Interestingly they are now making flower heads at ground level or just below ground level (I cut these off as well). I’m wondering at which point It will be safe to dig the ground over again. I plan on incorporating gypsum and compost as the ground is pretty hard, then getting rid of the couch grass which is thin on the ground in winter and lets in lots of weeds, then planting buffalo grass.

    Replacing couch with buffalo sounds like a good plan, Ann. The gypsum and compost sounds an even better idea because these weeds thrive in soils with poor nutrition. Healthy lawns will out-compete them. If you don’t have enough compost, an application of complete organic fertiliser each spring will keep your lawn growing strongly. Don’t cut your lawn too short as this reduces the area of foliage grass needs to photosynthesise to create the carbohydrates used for energy, and weakens the roots. It might be a good idea to check your soil pH too, as the soil pH controls the availability of nutrients to plants. – Lyn

  9. I’m looking to buy a 6 hectare property that’s full of onion weed, I’ve identified it as romulea rosea. I want to produce grazing pasture for horses. As not one to like the use of strong herbacides would elevating soils ph and seeding rye clover be enough to eradicate this weed?

    Hi Kaye, the post I’ve written is for onion weed, in which I accidentally wrote ‘onion grass’ in one place. I apologise for that. The weed you have is different and, as onion grass is often found growing on limestone ground, raising the soil pH won’t help eradicate onion grass. Perhaps this website may help with your problem: Onion grass

  10. I would like to thank you Lyn Because I also have masses of onion weed in my lawn I have just brushed them with straight weed killer But next week I will cut it all down to ground level many thanks June

    You will probably have to cut it several times, June, until the plants have exhausted the carbohydrates stored in the bulbs, but I heard on a gardening show at the weekend that weedkiller applications have to be repeated too, to kill them off. Give your lawn a good feed of a complete fertiliser (not just nitrogen) and don’t mow it too short. A strong, healthy lawn chokes out this weed. – Lyn

  11. Thank you so much. This is very informative. Most other websites just say to dig them out with lots of soil around to prevent small bulblets falling off, but from my experience it is a losing battle and simply not possible without disturbing the roots of nearby plants. I will try cutting above ground portion.

    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

  12. Irene I have just used Round up on my Onion Grass which is under my Roses brought in by planting a potted plant given me by a friend !!!. But having read all your comments on shearing the onion grass i will change to that method and just hope I havent done any damage to my Roses might be a bit of a fight with getting under the Roses but well worth it by all your comments Will let you know how I go !!!

    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

  13. It took years to get rid of onion grass around my azaleas. Now I want it back. It was keeping lace bugs off my azaleas. I didn’t know. Now my azaleas,which have been here 50 yrs. are dying. I don’t know where to get some.
    Barbara, pest attack is merely a symptom that plants are stressed because conditions are not to their liking. Onion grass prefers soils of low fertility. Do you feed your azaleas? Do they have adequate water to allow them to absorb the nutrients they need? If your azaleas started dying after the onion grass was removed, how did you remove the onion grass? Did you dig it out or use a herbicide?
    To get rid of the azalea lace bugs, use a horticultural soap spray. These are potassium-based and different from ordinary soap sprays, which can burn plant leaves. As well as killing the bugs, the potassium ingredient also strengthens cell walls, helping plants to resist pest attack. Natrasoap is one brand you can use, and Yates also have a horticultural soap spray. – Lyn

  14. hi everyone…. just joined and hoping someone can help out with a small problem. On my property , there is now a large amount of onion grass growing down on the river flats. The soil is quite good but nothing has been grown on this land in the last 25 years. i have had all sorts of weeds growing over the years ,now it is the onion grass’s turn. Is there any way that i might be able to get rid myself cide of this stuff, without resorting to herbicide. Thanks
    Hi Jimbo, if you keep mowing the area as short as possible so that the weeds can’t photosynthesise you will get rid of it (but it won’t happen overnight). The weed needs green foliage to convert CO2 into energy for growth. If you have a very large area covered with onion weed, you obviously can’t cover it with black plastic but continually depriving it of the opportunity to grow will kill it off. Trying to dig it out only spreads it. – Anyone else, any suggestions? – Lyn

  15. Thanks for info. I was wondering how to tree the situation when onion weed is growing after you mulch on top of the mulch????!!!!
    You may have to cut off the foliage at ground level several times, Sarah, before the bulbs are weak enough not to produce new growth. – Lyn

  16. 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?

    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

  17. l have had more and more onion weed each yr and this yr now that the tops have died off the pods have come 2 the surface, so lm getting out as many as possible and are going 2 put some in pots and some in2 another garden bed where its hard 2 get anything 2 grow…… l cant wait 2 put in2 my food and l will be cutting off leaves and putting in2 freezer 4 off season….lve had them on pizza be4 and they are delishes.

    It is unwise to recommend eating weeds based on their common name only. Onion weed (Nothoscordum inodorum) is a member of the onion family but is often confused with Onion grass (Romulea rosea), also know as Guildford grass, which is a member of the Iris/Crocus family and produces bulbs what we, as children, called puddings. This plant has no onion smell or nutritional value, and I would not recommend eating it. It also reduces crop production in garden beds, and the treatment is the same as that for onion weed. Incidentally, Jackie French does not include onion weed in the edible weeds section of her book. – Lyn

  18. Hi, I’ve just joined and that is mainly due to your advice on how to eradicate onion grass – having a problem with it at the moment and your solution is ever so simple. Have a nice day all and catch your later…..:)

  19. Hi, I’m new to this site and would like to thank you for the great advice about onion grass. Thanks!

  20. hey im into finding uses for weeds such as medical and for food does anyone have info
    Matthew, it is not a good idea to self medicate with any plants as the strength of the active ingredients can vary greatly with the growing conditions and it can be easy to overdose. As far as using weeds for food – Jackie French’s book Organic Control of Common Weeds contains a section on edible weeds. – Lyn

  21. in our community garden where nothing is growing bare sandy soil very small pebbles supplyed by the council is where onion grass is growing but not sure if it is onion weed has puple floers doesnt grow to high its like a grass can some one send photos of onion weed young & mature extra

  22. 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

  23. …Or… you can treat it as a veggie and eat it!
    Onion weed is fantastic stuff, sort of like a cross between onion & garlic. It’s a great addition to all sorts of meals, and even makes fantastic fritters when dunked in batter & fried. You can even eat the flowers. And eating it is a surefire way to get rid of lots of it, unfortunately!
    Since discovering how tasty this stuff is I treasure it – it’s no longer considered a weed in this house.

  24. We have a lot of onion weed in our paddocks and after watching flocks of galahs scratching and feeding on it ,I’ve used my chooks to dig it out and eat it .They love it as much as the galahs . In our hard cracking clays the small bulbs are just under the surface . They eat most of the other pasture as well but their manure makes up for it ..Probably harder to put the chooks through a garden bed unless you put them in a dome pen and move it around .

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