Green concrete !! :)))

Plenty of Info out there do a search on google .You could try this tip below I dont know if it works
Don was asked how to get rid of onion weed. He said that the only way was to spray with a glyphosate-based product, such as Roundup or Zero. Trying to dig out onion weed will only make the problem much worse. There may be thousands of bulbs in the soil and they'll keep coming up, so persistence is the key. It's a good idea to have some spray ready so that you can repeat spray whenever you see new shoots appearing. If there are other plants nearby it may be best to apply the glyphosate with a small paintbrush, to ensure it only makes contact with the onion weed and not plants you want to keep growing well.>

VERY difficult to shift.
Metsulphuron ('Brush Off') will certainly work but is expensive. You may be able to group share the cost with others with the same problem?
You might try Solarising. Wait until the weather becomes hot, water the onion weed well,lay black plastic over the area and leave it there for a few days to "cook" under the plastic. Sometimes works, but the days need to be HOT

Try pouring a few drops of machine oil onto the crown. This will cover the bulb and kill it. It really works, believe it or not. I tried many things, and this is the only one which worked.

I remember when I was little, my Mum had an ongoing battle with clumps of onion weed at the back of the house. I'm not sure what she used, but I know they cam back again and again over a number of years. But then she finally solved it, and it worked to perfection.

We built an extension over the top.

I have/had a clump of onion weed in my garden and tried everything, using machine oil would take forever to apply. I have had some success by smothering it - thick layer of newspaper topped with mushroom compost. I watch the area like a hawk and whenever a shoot appears I hit it with Glysophate (I heard Peter Cundall say recently that mixing Sulphate of Ammonia with it makes it super effective, so worth a try). Good luck

Why don't you try digging the majority of it out, then applying the motor oil? Either that or spray with glyphosate every day until they eventually die. Don't let them get the better of you!

Timing is everything in getting rid of Onion Weed. Needs to be sprayed while vigorously growing. eg: back in June-July, not now when it is going dormant. Broadacre farming areas have done this, sprayed whole paddocks out, but the timing has to be right, it works, with Glyphosate too and I would think with a wetting agent added.
Joylene

You could try a flame thrower, a bazooka, TNT, telling your friend on an unsecured phone line that the b.o.m.b.s are hidden under the onion weed, moving, or adding some liquid detergent to your glysophate, which 'cuts' through the waxy coating on the onion weed leaves allowing the glysophate to do its work. You don't need to add very much.

I THE ONIONE WEED AS TOOK OVER MY LAWN WHAT TO KILL IT ALL THE PUT NEW GRASS DOWN

Once-a-year weed killer will do it but I found the best is kerosine - a little poured over each plant. Wait till all is dead and dried up (a month or two) then replace the soil, or leave it for a year or more.

I had quite a bit of it in my garden bed, there was so much of it that is was impossible to dig it out. There were plants around the onion weed so I carefully sprayed the foliage of the onion weed with round up.

The plants around the are still good, the onion weed is stone dead. Digging it out works but the seeds attached to the bulb of the plant means you'll be doing this exercise for years to come.

I'm a terrible gardener, but I'm a Round Up fan.

Mark