Yes, they do get that big and sometimes even taller. I had one plant that reached well over twelve feet tall because it was planted in a semi-shady area. Most times Hollhocks do not need to be staked (unless the flowering top gets too heavy for the bottom to support).

They love well draining soil. They don't seem to fussy about soil type though.
It is difficult to transplant these plants because they have a long tap root that does not like to be disturbed. It is always best to transplant while they are still small. If you must move your hollyhocks dig several inches away from the plant all the way around it. Do it gently so as to keep the roots from being too disturbed in the move.

Hollyhocks are bianulas, which mean they bloom every-other year. But often times the original plant will send out "babies" around it. These babies will usually bloom the year the orininal plant is not blooming.

My hollyhocks re-seed like crazy, and in the most unusual places (like cracks in the sidewalk and inbetween pavers). They are hard to get out. They are prone to rust and aphids. You can spray for the aphids, but I have found that there is not much you can do about the rust. Even in the the best of locations it will get rust.

I have some planted in places that range from full sun to almost full shade. I find that they do well in both places. In my yard the ones that always look the best are the ones that are planted in the shadier location that is also on the moist side. The foliage will be larger and look nicer. The ones that are in full blazing sun and dry area don't look quite as full and the bottom leaves get yellow. If you do plant them in full sun consider planting them in the back of the boarder so other plants can cover up any unsightly foliage.
Hope this has helped you some lifeblessings!
CMK

Just realize that if japanese beetles are an issue in your area, hollyhocks seem to draw them like bees to nectar. That is one of the reason I stopped growing hollyhocks even though they are certainly very gorgeous varieties of them!:(

As to whether they will need staking, it really will depend on the variety and your local conditions. I always had to stake them in my garden when I grew them, especially after they bloomed out higher up on the stem. These were also grown in full sun in zone 7a.

Z5 NH checking in...I had two last year that got nearly 7' tall and didn't *need* to be staked until the very last of the blooms were out and the seeds were set. At that point, they went horizontal and should have been staked, but I simply cut them back since they were nearly gone by anyway.

I am trying the more dwarf varieties this year- nothing over 5 or 6' this time, and some even shorter- "Fiesta" was one dwarf I found on the T&M rack.

thank you for the great answers! what I understand is that they are sturdy enough to be on their own until they get too top heavy with bloom... Are they dependably perennial if mulched and cut back? How far should I cut them back after bloom?