I do not have a direct answer to your question, but my experience is, that single rosettes planted in autumn have lower survival rates than bigger clumps. I have read it also in a catalogue . I just do not have an explanation for this phenomenon. I've decided to discontinue planting bought heleniums in autumn.

But I'm talking about spring dividing - like right now since the plants are only a couple of inches tall. I've always divided them this time of year in the past and like I said, by midsummer they're 3 feet tall.

I've noticed my plants don't produce the rosettes we're talking about until very, very late in the fall. That's why I've never tried dividing them at that time. In my climate unless perennials are divided by late August or so, chances of survival go way down - depending on the particular plant of course.

Kevin

Do it now. I just did this with Mardi Gras and Double Trouble. Now is the time. They all should do great!

Agreed, they are so vigorous, if you want more, might as well divide them...I've never lost a plant yet!

Firstly, ONE rosette can only produce 1(one) flowering stem. NO MIRACLES here. There can only be difference in how many side branches an individual stem will develop(big differences depending on variety and general health)

Secondly, not all Heleniums are equally vigorous. There is a big difference between the various varieties. Ruby Tuesday produces very few daughter-rosettes for me.

Thirdly, a big and strong stem can produce more daughter-rosettes than a thin and week one. Daughter-rosettes can only bloom following year.

OK, I did the deed, divided it and did note a difference in the growth habit of Mardi Gras vs. the ordinary one mentioned in my original post.

With the ordinary one, it made no difference how small the divisions were. A single rosette still produced a blooming sized plant by midsummer. However that plant also separated into individual plants much easier when dug.

When I dug the Mardi Gras, I actually had to cut the clump into divisions. I ended up with 3 clumps, each with 4-5 rosettes, but I didn't feel comfortable trying to make any smaller divisions. They just didn't separate easily like my other plant.

So wieslaw, I agree. Not all Helenium are created equal in my extremely limited experience.

Kevin

I don't dig mine up at all. I just wiggle the side stems back and forth and they come right up with roots on them. I was able to do both the same. "Double Trouble" is a more robust plant than "Mardi Gras" but the process was the same for both. I guess it just depends on what you're comfortable with doing to your plant. I like that these are so easy to multiply. I have found that I can do the same process with Coreopsis, Amsonias, and Echinaceas as well.

um, there is some difference in vigour - for example, autumnale is much more vigorous than Sahin's Early....but, they are all amenable to regular division - at least every three years and even more frequently. Also, like asters and rudbeckias...in fact, most later flowering perennials, I never divide and plant in the autumn but wait till the following spring.