I'm curious as to why they've recommended epsom salts- is your plant suffering from something currently? If its not, you're best off watering when it needs it, and feeding from spring through summer with a liquid, balanced NPK fertilizer, such as Growmore (comes in a liquid as well as granules) once a month, no more. They don't need a lot of feeding so a feed around now, one at the end of May and one in June will be plenty. Alternatively, just apply and lightly fork in a handful or two of Growmore granules, and don't give it any more this year, its not essential. On the subjecty of epsom salts and the expression 'greening', it doesn't mean it will turn the foliage green, it means it will improve the colour of the foliage on the assumption its green in the first place. I wouldn't use epsom salts anyway, I'd always recommend a balanced feed. Link below for more info

https://www.rhs.org.uk/advice/profile?PID=543

As Bamboo says, Epsom Salts (Magnesium) will do little to a purple Cordylne. The balanced fertiliser will surffice though in the wild they flourish without any. If this is type of advice you can expect from your garden centre, I'm afraid I would give them a wide berth in future.

May I thank you for your swift response. The garden centre where I received this advice was Van Hages in
Peterborough. I will take your advice and get some Growmore granules instead. The reason I inquired about
the plant was that it was beginning to look a bit colourless and not as it was last year. May I thank you once again
Regards
Bytheby

A Cordyline with magnesium deficiency--which is what Epsom salts corrects--will have brown tips and edges to the leaves, and the remainder of each leaf will be a tired yellow green, or, in the case of purple Cordyline, a orangish color. Nitrogen and potash deficiencies are more common, however, so Epsom salts would be considered a supplement to regular--though not frequent--applications of a good balanced plant food. Some commercial plant foods have magnesium in them, but I don't know about Growmore. You might want to check the guaranteed analysis on the back label.

No magnesium in Growmore, Tug - but I'm willing to bet this cordyline, if its been outdoors all winter, or wrapped up in fleece all winter, looks awful because of winter rather than its being any shortage of nutrients... and if the lower leaves have a faded appearance, they're just getting ready to fall, which is, as you know, perfectly normal. A better guide to whether it lacks nutrients will be what the new growth looks like...

All true, Bamboo. My own experience may be skewing my advice again, since I have to feed so much more in my climate.
Bytheby, more details on exactly how the plant has become colorless, or pictures, would help us find a more exact solution.