Amazing as they may be, horsetails aren’t a plant wanted in most gardens. They’re incredibly tough: that is part of what has helped them to survive for millions of years, but it’s also part of why they’re so difficult to deal with in a garden situation.
Nevertheless, they are fascinating plants. Our UK species, Equisetum arvense, has two distinct forms: a pale, non-photosynthesising but fertile spore-bearing stem comes first and lasts for only a few days. These are just beginning to appear now in this area. As they first start to appear you could almost mistake them for a type of fungus.
The fertile stem is followed by a sterile, but photosynthetic, green stem that lasts through the summer. The initial fertile stems often go unnoticed because of their bland colouration and slender shape. The plants are spread by their spores and also vegetatively by their rhizomes (they don’t flower or have seeds).
Garden Organic has a useful factsheet about horsetails and their management (i.e. how to get rid of them) in organic systems.
Chemical control products are available, but even they need repeated applications over several years.
Horsetails are potentially poisonous to humans and livestock. However, livestock would have to ingest a significant quantity of plants before damage would occur: it isn’t a plant to panic about from that perspective.
For humans, although they are poisonous, they are also edible…but care needs to be taken in their preparation. See the Plants for a Future database for more information on this. Personally, I wouldn’t eat them (for one thing, their name sounds too much like ‘a queasy tum’ which is off-putting in itself!), but in some countries, they’re considered a delicacy and have a long culinary history.
If you have got horsetails and you want to get rid of them, you need to accept it is going to need quite a long term strategy. And if you employ a gardener and they tell you differently, be very skeptical!