My Garden Nemesis: Horsetail (Equisetum)

The horsetail family is often called a 'living fossil', this is because Equisetum is the only genus left of Equisetaceae, some members of which were trees growing 30 meters in height.

I think my nemesis is Equisetum arvense, the field horsetail. In some ways I'm lucky because the fertile heads that release the spores are only present in the Spring, whereas other species have fertile heads year-round.

While the plant is botanically interesting because of the silica that it deposits in its stems and leaves, especially rough horsetail (E. hyemale), which used to be used for scouring pans. Also because it can be apparently boiled in water to make a mildew fungicide for plants such as roses, and not forgetting the fact that it can be taken apart and put back together like lego (hence another name 'Lego plant'), but it is a gigantic pain in my garden and most of my energy each year is wasted keeping it under control.

This is only the beginning :(

Last year I read an article that described horsetail spores as being able to move around. So, in a bid to get to know my enemy a bit better, I decided to take a fertile head into the house and check the spores under the microscope.

I was surprised by just how green the spores are, but not how horribly numerous. Their tiny size of 50 µm hides the fact that once these things germinate they develop deep and creeping roots that are incredibly difficult to control. Even deep cultivation is likely to break the plant up into small pieces that are able to regenerate. We go for the option of pulling as much as we can reach as frequently as we have the energy in the hope of reducing the stored energy of the plant over time. It's a long term approach and as the whole street is 'infested' with horsetail it's likely to be a never ending task!

However, back to the spores!

The spores, along with being green, has 4 elaters, which are basically appendages that allow the spore to move. This movement is random and seem to be driven by cycles in humidity. During my observations, I noticed that there would be a mass movement for the first minute or so after release from the sporangium, release from which seems to be one of the three reasons for movement given by Marmottant et al. The other two being to reorient and to refold and ensures an annoyingly efficient dispersal. If you'd like to read more about horsetail spore movements, I recommend you read The walk and jump of Equisetum spores by Marmottant et al, which is available in full here.

You will also be able to find better videos of horsetail movement online, but here is the footage I captured with my microscope:


I am always open to new ideas about managing the 'horsetail situation' as long as it doesn't mean poisoning my garden or concreting it over! Please let me know what works for you in the comments below.

Thanks for reading!

References

Mabey, Richard. Flora Britannica. 1st edition. London: Chatto & Windus / Sinclair Stevenson, 1996.

Marmottant, P., Ponomarenko, A., & Bienaime, D. (2013). The walk and jump of Equisetum spores Proceedings of the Royal Society B: Biological Sciences, 280 (1770), 20131465-20131465 DOI: 10.1098/rspb.2013.1465