I would definately look into Musa basjoo. With a good thick ground mulch for Winter they should bounce right back in the Spring. I do know of a few folks in southern Ontario that over winter this species of banana. They should be root hardy down to -20 C. With a zones worth of mulch or two who knows? They will give you the ultimate display of large tropical leaves in no time flat. Cheers, Banana Joe

I love, love giant plants. One of my favorites is ornamental rhubard, rheum palmatum. I can't grow gunnera here but I'm very happy with my big rhubarbs! This year mine bloomed up to well over 10 feet and the foliage wasn't far behind. They get better every year....
Faith

Ornamental grass. I have a miscanthus sinsensis giganticus or goliath. They are very hardy, and make a wonderful statement at over 10 feet tall.

My castor is beautiful at well over 10 feet, but it is not hardy. Unfortunately.

I also use the large 5 foot tall cosmos. They are really impressive, but once again are not hardy, but cost peanuts to grow.

Arundo donax is nice as well. You could also give some Yellow Groove Bamboo a try. It is a very cold tolerant tall growing species. Cheers, Joe

Happy to recommend a plant that I really enjoy having in my garden - and it is very hardy. It is called Inula Magnifica - I think the "magnifica" refers to its size and height! This will go to 6 feet tall! Thick stems with slight purple blotches support foot-long, fuzzy and serrated leaves and end in bunches of bright yellow flowers (to six inches wide)in a daisy-like shape, with thread-like ray florets. It is amazing that this plant, so huge, has flowers so delicate and elegant. Try Googling this plant and you will see lots of photos. Good luck!

I love it Shapiro. Beautiful plant. That is a good one to get.

A few more suggestions for some good-sized plants, if not exactly giants:
Cephalaria gigantea - about 8' tall; very open and "see-through"; doesn't need staking;
Thalictrum delavayi 'Hewitt's Double' and Cimicifuga racemosa - over 6' tall in the same humusy, moist soil conditions;
Valeriana officinalis - about 8' tall with fragrant, early bloom;
Eupatorium cannabinum flore pleno - just under 6' tall, and about 3' in diameter....

Although my yard is small, I can still appreciate the big ones! :D

Some hostas are humungous (sieboldt Elegans, for example)
Ligularia Prezwalskii
Cimicifuga
Helianthus
Cortaderia (ornemental grass grows to 6 ft or more)

Silphium perfoliatum - cup plant.

Thanks for the ideas - keep them coming.

I didn't know where to put a 'giants garden'. Most of my areas are near large trees and I was afraid the large trees would take away from the plants size. but I figured it out. I have a hill that I plan to turn into a shrub garden - mostly things under 10 ft. I plan to put in a path and line the plant with giants - a kind of giants walk.

Acanthus, Bear's Breeches, beautiful, bold leaves.........Wayne

There's also Telekia speciosa (Bupthalmon), big leaves, nice thick sturdy 1" + stalks, grows to 5', flowers similar to Inula. Will take part shade.

Hollyhocks from 'Happy Lights' Mix, grow to 12-15 feet tall.

Lavatera arborea variegata, 6', lovely large velvet leaves.

Aralia cordata is a plant with huge compound leaves and clusters of white flowers quickly followed by purple berries which are much loved by birds. I recommend rodgersias which have lovely flowers as well as big leaves (I grow a few different ones and love them all). Astilboides tabularis is one of my favorites, though it takes several years to reach its mature size and it too has pretty flowers. If you have the room, petasites giganteus is a fun, unique giant of a plant. Some of the hardier spuria irises can reach 6 feet or more.

I've grown all of those (except the spurias--added them just last year) for many years in a colder zone than yours with no added protection, so I can vouch for their hardiness.

Good luck with your giant garden,

Kate

Kitaibelia vitifolia is big & exotic & grows to zone 5.

Helianthus salicifolius - Willow leaf sunflower. Here, it grows about 10' tall, and with it's narrow leaves, looks like an ornamental grass until it bursts into bloom in autumn.