Mine get to a height of a about 4 ft. Roughly 12-18 inches of that is flower spike. Not as tall here as in some areas, but considering they're not really considered hardy here, I'm happy with what I get. after about 13 or 14 years I had 5 flower spikes on one and 4 on the other of the two bulbs. I planted three originally but one didn't make it. At least for me they seem to multiply slowly. I read somewhere that division every 15 years is about the average. I would guess this is dependent on your conditions and how closely they are planted initially.
Even a single bloom stalk draws the eye. As for underplanting with daffs, I can't really answer that.
Hopefully someone else will chime in, I'd love more info on them as well, as I'm wondering if I should divide mine this fall. I'm torn between leaving well enough alone and seeing what I have down there.

The tuteur is 3 foot tall, so these foxtail lilies, Eremurus 'Roford', were only a little taller than that when the picture was taken some years ago. My bulb list says that this variety gets 30-48 inches tall. They eventually got a little over 4 foot tall, because I remember being surprised one year to see them well above the tuteur and the Clematis tangutica 'Sheriffi'.

I also started with 3 roots (quite large & strange looking, as I remember) & after a few years had 7 or so flower stalks. Foliage at the bottom was minimal. I planted them in my gravel bed, gave them no care whatsoever, no fertilizer (this particular clem doesn't need any, very vigorous), no supplemental water, left them up over winter & they did fine until the gravel bed flooded one season & rotted (I presume) them out.

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P.S. white flower to the left bottom is a penstemon, either Husker Red or Alba, I still have both in that bed.

Wow - great tuteur & thanks for the info. I think I'm going to plant a couple of staggered rows. The building is 3 stories high, so I could really do with some height at the back of the bed!

Crossing my fingers that the foxtail won't be messed up by having daffodils come up from under in the spring...

The Foxtail Lillies(3) was a mail order specimen for me and I ammended the soil with sand and formed three peaked hills in a dug out hole carefully placed on top. and backfilled with sandy soil at correct depth. They've got to be extremely well drained. They came up but not as vigorously as I thought the following spring Does anyone know if there is something that would give them a good growth boost ? I'm thinking 20/20/20 fertilizer but unsure? Thanks