Eradicating Onion Weed


Onion Weed

I help out a friend, doing her garden half a day per week. At this time of year, (spring) too much time is spent getting rid of Onion Weed (Nothoscordum inodorum) which has spread over large areas of the garden. It spreads by both seed and tiny bulbils which form on the main bulb in their hundreds.  (see photo)

Depending on the situation, there are a few ways the job can be done and I am using a combination of the following.

POISON

First, remove any flower heads as they will remain viable even after poisoning.

Onion Weed bulbils

Glyphosate is quite effective, especially mixed with a little ammonium nitrate or ammonium sulphate at normal foliar fertiliser rates. The leaves suck up these nutrients along with the glyphosate. If it is not already in your glyphosate product, you can also add a few drops per litre of detergent, to overcome the repellence of the waxy leaf coating. If there is any danger of overspray getting onto plants you want to keep, then you can use a broad paintbrush or if the infestation is thick enough, a paint roller on an extension to save your back.

Glyphosate will not kill off the bulbils unless they have sprouted above the soil, so poisoning may take a few seasons.

If you touch one of your valued plants by accident, remove the affected leaves straight away.

Onion Weed flowers and seed heads

PULLING OUT

This can be the quickest method, but requires a great deal of care not to spread the bulbils which detach themselves from the main bulb on the way out. I use a garden fork to loosen the ground under the bulb and slowly ease it out as you wiggle the fork up and down to further loosen the soil. Any bulbils left behind are usually nearer the surface and will be easy to remove when they sprout, either in this or the next season.

STARVING

In a lawn, regular mowing will eventually deplete the bulb of the food it needs to survive. In a garden bed where mowing might not be appropriate, I have found a sharp Dutch hoe (also known as a scuffle hoe) to be effective in removing the tops below ground level. The lower you cut them, the more reserves they have to use to grow back and the quicker they die.

If there are too many plant roots to use the hoe, you can use a thin bladed knife or simply pinch the tops off by hand and check at least weekly for new growth.

If the situation allows, black plastic laid over the top will prevent the bulbs from being re-invigorated by sunlight. In my experience weed mat is not effective for this purpose, nor is any translucent plastic.

Above all, be vigilant.

Jon