HelpfulGardener.com

Having recently bought my first house I inherited a garden of surprises.
The house had previously housed students for a couple of years, so as you might expect the garden had been horribly neglected and was massively overgrown, but once the hacking, slashing and uprooting was done (with some help!) it revealed a well laid out flower garden that someone had once but a great deal of effort into making and maintaining. So well set up that many of the original plants (which I can't identify as I know next to nothing about ornamentals!) are still intact and while there are obviously quite a lot of holes, the weed-suppressant combined with gravel mulch are back to doing a decent job.

Unfortunately there was a nasty surprise lurking in there, horsetail, and its everywhere. All throughout the front garden, which could reasonably be poisoned, but its growing between the leaves of plants in the back garden too where I can't use toxins.....
Digging it up isn't feasible and I obviously can't just pull it up so is there any other method of getting rid of it?

Third year now of dealing with a horsetail problem and they are beginning to give up the ghost. This is an area of paths and rockeries which tend to not be tilled and hence give a great breeding ground for horsetail.
On the 8th May 2017 I noted on this forum having removed 100, today just five. I suppose the horsetail season might be late from the Beast from the East. However, I reckon removing individually with a long narrow headed trowel on a weekly rota and tilling the area with trowel and they will get weak and give up eventually. Read somewhere, five years to eradicate like this.

the old saying is "one year of seeding makes for seven years of weeding"
for those areas twixt the posies that you are afraid of pulling for fear of losing the flower, try clipping as close to the ground as possible with a pair of scissors or garden shears. being annuals, they should die out over the winter, and keeping them from going to seed will prevent the next year misery of another crop.