Older Pincushion plants do have a tendency to get scraggly, but in general they are quite easy to grow. If yours is dying back without apparent reason (no noticeable insects, overly dry conditions, etc.), it could be a signal that the plant has sustained some type of root damage from excess moisture. Roots can sometimes stand in too much water over winter, leaving them susceptible to mold and rot during the growing season. Try cutting your plant back to the ground this fall. It might be enough to restore it for next season. Make sure you mark the spot where it's planted so you don't accidentally mistake it for a weed next spring. If the roots have sustained too much damage, there is probably nothing you can do to bring it back. In that case, plant another pincushion plant next year, but consider planting it in a raised bed with plenty of drainage.
I did a quick Google search and came up with a couple of things. First off, is this a cacti? I have found several different plants commonly called "Pincushion". Here's a URL for cacti care: www.plantideas.com/
Good luck!
