Around this time of year, a lot of gardeners seek answers from gardening gurus, books and the internet to their onion weed or bindii problem.
Treating onion weed and oxalis with glyphosate will only kill the parent bulb – not the tiny bulbs that are loosely attached to the base of the main bulb. Onion weed also tends to be resistant to normal strength herbicides and gardeners have said that they have to use undiluted glyphosate. In garden beds, this can create other problems. Glyphosate is not broken down on contact with soil. It binds to certain soil compounds. When soil conditions change, it can become unbound and affect later crops. Soil-borne plant diseases are also more common where herbicides are used.
Get Rid of Onion Weed
For an effective way to rid your garden of onion weed, see Onion weed treatment
Get rid of Bindii
Bindii or Jo-jo needs to be treated in early winter before the vicious spiky seed heads form. It is far more difficult to eradicate this weed later in the season, see Bindii or Jo-jo
A lot of gardeners seem to be having problems with onion weed lately. To compound the problem, there is some confusion about what is “onion weed”? Nothoscordum gracile, or N. inundorum, or Asphodelus fistulosus are all referred to as onion weed in various articles. Onion weed is often confused with another weed (Romulea rosea), that is known as “onion grass” or “Guilford grass”. As children, we used to call them “plum puddings”.
Basically, the treatment for all these weeds is the same and can be found on Aussie Organic Gardening in this post.
To help indenitfication, you can see images of these weeds on the links below.
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.
In order to eradicate problem weeds, including Nut Grass, Onion Weed, Sour-sob (Oxalis), and Tradescantia (Wandering Jew/Creeping Jesus), it is necessary to understand how these plants reproduce, because merely digging, or pulling out, these weeds is rarely successful.
Wandering Jew or Creeping Jesus is a weed of moist, shaded places. It produces extra roots at the stem joints where they touch the ground. The stems snap easily when pulled, allowing small pieces of stem to remain in soil and produce new plants, making it difficult to completely eleiminate in one go.
You can tackle this weed by whipper-snipping or cutting off as much above ground growth as possible. Rake it up and dispose of it in a sealed plastic bag. Then cover the area with black plastic or weed mat anchored around the edges. It likes damp soil, so the black plastic is best – it will prevent rain getting to the soil. Excluding light also prevents the plants from manufacturing food for future growth. Then, the most important part is to go around the outer edges of the plastic with a sharp spade and cut through any underground runners that may be extending beyond the plastic, otherwise these parts will keep supplying the runners under the plastic with food and moisture to grow. It can take up to a couple of months to kill off this weed.
Nut grass, onion weed, and Oxalis or Sour-sob release small bulbs (bulbils) into the soil when plants are pulled out, or when soil is disturbed by digging, which rapidly increases the number of weeds. During each growing season, these weeds use sunlight, carbon dioxide and water to manufacture glucose to use for energy. The glucose is stored in the bulbs and bulbils during a period of dormancy to be used for growth in the next season (in the same way as spring flowering bulbs).
The way to eliminate this type of weed is to prevent them manufacturing food through the green parts of the plant. This can be done by excluding light and water for a couple of months with thick cardboard or black plastic. If these weeds are a problem where they are close to plants, repeatedly cutting off the foliage at ground level will eliminate them.
If they are growing in a lawn area, improve fertilisation and watering of the lawn. A healthy, vigorous lawn will smother these weeds.