i tried to google your plant name.. and it SEEMS that it is an annual ...

so i dont understand why yours is multiplying ... in z5 .... rather than re-seeding ...

are you absolutely sure on the ID???

if it is a perennial.. and it is developing a fairy ring.. there would be no reason you couldnt cut it at noon, 3, 6 and 9 o'clock .. and move out 3 of them ... and then have 4 new clumps ... if in fact it is a perennial ...

but a true ID would sure be a better starting point ...

ken

ps: i dont mean time of day .. i mean on the clock face ... lol .. 0, 90 degrees, 180, 270 ... and i dont mean temp.. oh for crying out loud ... lol

Helianthus 'Lemon Queen'.

Yes, it probably should be divided. I'm waiting for the garden gnomes to show up and do mine, since I nibbled away at the edges last year, and decided it really was at least as big a job as I thought it would be. For one thing it has a very fibrous root mass that doesn't separate easily. Cutting pieces out with a spade may be the easiest thing to do.

Yes, I think a large spade or shovel is needed to divide this large plant. I have a few clumps and it does spread a bit. It also will self-seed.