The GARDENA gardening expert
Dear Ms. S., the common horsetail has always been difficult to deal with as it takes root around two meters deep and it is because of these roots that it is practically impossible to dig up. That is why digging very deep and breaking up the bed was not effective. You can kill the plants by covering the bed with a film (black, opaque) for several weeks during the summer.
However, this is relatively expensive. Another option is to try a new environmentally friendly herbicide supplied by Neudorff (it acts on a base of pelargonic acid and maleic hydrazide and is called Finalsan AF GoudweedFree), which also works well against common horsetail — you can practically see it dying after the product has been applied. I have used it against ground elder late in the morning and the plant had died by midday. You can even send me a before-and-after photo; check the time to see how long it took for the horsetail to collapse after the product had been applied.
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