Anyone who has ever worn socks in Summer or owns a pet will know Burr Medic (Medicago polymorpha)! It’s spiny little seed cases get stuck in anything fibrous weather man made or furry. It is equally a curse for folks who like their lawns immaculate.
But that’s all a human centred view. In our ecosystems, it has several valuable uses.
We just have to face it, Nature doesn’t like bare soil and does whatever she can to cover it. Bare soil is seen as a wound and needs to be protected and restored. That’s where Burr Medic comes in.
This tough little plant is a coloniser that excels at its job. Its mat of leaves act as a bandaid for the bare soil, covering it and protecting it from further damage. Burr Medic has other uses too. It has a deep taproot that penetrates deep into the soil, breaking up compaction. This taproot brings nutrients to the above ground parts of the plant which, when they die, add them to the surface as organic material which can be further broken down my various microfauna. This organic material also protects the soil from damage as well as increasing its water retention capability . When it dies, the taproot provides convenient food for soil fauna and when digested, leaves a path for water and oxygen to penetrate into the soil.
Burr Medic is a Legume too and, like the other well known members of that Family (Leguminosae) Beans and Peas, provide nitrogen to the soil which is invaluable in so many biological processes. The nitrogen fixing bacteria which do this job are located in nodules on the roots and when the rest of the plant does or they are broken off, they decay and their valuable cargo of nitrogen makes its way into the soil. The bacteria need to live inside these nodules because the process by which they gain energy and fix nitrogen is an anaerobic one (that is, without oxygen) and the walls of the nodule keep the oxygen out.
The tiny Pea flowers (which help to define its Family) of Burr Medic provide a food source for many tiny creatures, both pollinators and predators, greatly increasing the biodiversity that would be lacking on bare soil.
As with many coloniser plants, Burr Medic produces a prolific amount of seeds and has an effective dispersal mechanism the tiny hooks on the seed pods snag into anything furry that brushed against them and they are, thus, transported further afield.
Interestingly, at Ligaya Garden, we have only been graced with the presence of Burr Medic since I started regularly mowing the road verge. Before that, we saw it only in neighbours gardens and in other verge areas but now it’s here. It’s a pain to have and even the kindest thoughts and recognition of its role don’t endear it to me but it does it’s job well and I’ll leave it on the verge and just pick off the occasional specimens that pop up inside the fenceline.
If you must remove Burr Medic, there are several methods that you can try before reaching for the herbicides.
Because it is a coloniser, it tends to minimise its presence once the soil is repaired. Adding goodly amounts of organic material to increase water holding capacity and soil structure is a good way toward deterring it or getting rid of it.
The seed pods are a problem that is best dealt with by regular removal such as mowing before it sets flowers and seeds. removal of the crown at the soil level leaves the organic material of the taproot to decay in the soil. Once seeds have been set, laying an old blanket over the area can pick up a lot of them. Then you just need to pick them off of tee blanket and dispose of them.
Burr Medic germinates in late winter so observation and removal of the young seedlings can help stop it from getting a foothold. At this stage, I pour boiling water over more established plants and that kills them off nicely.