How to kill Oxalis

Johannes Ulrich Urban via pbs
Mon, 12 Oct 2020 16:08:55 PDT
Hello Pamela,

Killing Oxalis is not that difficult if you have enough time. I 
understand that you removed all plants you want to keep from the 
infested bed so that there is no need to care for any desirable plant 
amongst the weed.

If you have time to wait a full growing season, my recommendation is to 
cover the whole bed with a material which excludes light. I understand 
that the Oxalis in question is not Oxalis pes caprae but another species 
which produces bigger bulbs than pes caprae. But to my knowledge any 
bulbous Oxalis forms a new bulb each season (Please correct me if I am 
wrong). To do so the plant needs light to photosynthesize.  My 
recommendation is based on the experience I made here in Portugal with 
Oxalis pes caprae.

Some parts of my new garden are so heavily infested with this Oxalis 
that it smothers practically everything else. It gets worse when the 
soil is worked, especially after rotovating. So I used the woven black 
plastic cloth which is used in nurseries to stand potted plants on. It 
lets air and water through but not light. (There are different qualities 
available, use the heaviest one) This was spread on the soil after it 
was rotovated, raked even and the cloth  fixed with stones. The Oxalis 
sprouted beneath and was so dense that it lifted the cloth from the 
ground but the shoots were pale yellow. I walked over the cloth to 
smother the pale shoots under the plastic and to avoid it being lifted 
high enough to let light in at the edges.  The plastic was left until 
late spring and and then the area was planted with vegetables and 
irrigated. To my surprise in autumn, when Oxalis pes caprae started to 
sprout in other parts of the garden, nothing came back in the previously 
covered area. I was apprehensive because the shoots were so dense under 
the cloth.

This way I did not use herbicides nor did I do any weeding. But the area 
was clear of any plants and could be covered entirely and I had the time 
to wait. I use the same technique now in between established plants 
regardless if the weed is winter or summer growing or both. A good 
material is strong cardboard which is flattened and weighed down with 
stones (I have plenty of stones...) Cardboard lasts long enough to kill 
the Oxalis or other weeds but then disintegrates and can be worked into 
the ground like other mulch material. Sometimes I also use cut open 
compost bags. They are of strong plastic and resist the UV light but 
have to be removed and do not let air and rain through. it is okay in 
small patches. A disadvantage of these methods is that they privide 
cover for pests like rodents or slugs.

I would also like to share another experience I made with Oxalis: I lost 
a whole collection after it moved from my old greenhouse with acrylic 
glass in the roof to the new one with laminated true glass in the roof. 
The building permission for the new greenhouse forced me to install a 
laminated glass plus an extra pane of safety glass which means in total 
4 layers of material. This absorbed so much light during winter (not 
detectable to the human eye) that my Oxalis dwindled away during two or 
three seasons. In both greenhouses the Oxalis was housed close to the 
glass in the roof.

I have no personal experience with the solarizing method Nan recommends 
but have my doubts that it would work in winter.

Hope that helps,


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