I believe most agapanthus are for zones 7 or warmer (maybe zone 6?), so if you're in zone 5 - you'll probably have to keep it inside for winter. The link below points to an article about zone 5 hardy agapanthus, but the author didn't have any success.

I grew a few pots of these for years and had great success overwintering them in a very sunny window, but very cool conditions - 50's F down to high 30's F. I also kept them very dry. They bloomed like crazy each summer. From what I've read, the cool winter temps are necessary, so don't try to treat them like a house plant.

After several years, I just got tired of lugging those huge pots inside every winter and they became compost pile material.

Kevin

Here is a link that might be useful: agapanthus

I grew some Agapanthus from seed, bought at Park seed, 7-8 years ago and put them in pots and took them in each fall. Three years ago I got tired of bringing them in because they had grown to really large clumps and left them out in my garden. They have overwintered very well ever since. I just have about 2 inches of woodchips for mulch. They are a little late to break ground but grow quickly once started. They are just beautiful in bloom, everyone loves them.

I cannot speak for that variety of Agapanthus, but I can say that agapanthus is much hardier than believed. I live about 2 hours nw of the city of Toronto and have been growing both white and blue agapanthus for several years now. Both are hardy and increase in size every year. I do not winter mulch plants but snow cover here is reliable. I planted the blue agapanthus at least 7 years ago, and the white agapanthus about 4 years ago.

This 'Blue Yonder' cultivar is supposed to be hardy to zone 5 from the info I've found so far. However, I am a bit skeptical since it sounds like very few people have grown this cultivar yet.

I overwintered Agapanthus once in a partially shady spot. Then it croaked. So did the supposedly hardy "Headbourne Hybrids" I raised from seed in a sunnier location.

It might be worth trying again in a more protected area, like up against the house in a southern exposure.* I certainly wouldn't try it with a plant I bought this late in the season.

*I'm making the attempt to overwinter a Crinum (C. americanum?) in just such a location.

I would also be concerned about the lateness of the season. Maybe keep it inside this winter if you have a cool spot and plant it out next spring. I would think once it has an entire growing season to settle-in, you would have a better chance of keeping it through a winter.

If you Google the topic, there is a lot of info about how to keep these inside for the winter. I believe I read somewhere where someone keeps these plants in their basement, totally dark and dormant for the winter, but you would have to figure out what works for you.

Kevin

My agapanthus is in an unprotected spot. The first clump I attempted to overwinter was near the house and it did not make it. I had wondered if the heat from the concrete steps awakened it too soon.
I am certainly not the only gardener here to overwinter agapanthus. I know that it is hardy near Wiarton, Ont., where I have several friends who grow it. Although Wiarton benefits from the lake effect, we and several other gardeners who grow it are well inland.
Try it. All you have to lose is a plant.

I post on the antique rose thread quite a bit and innocently suggested agapanthus as a change from hemerocallis. You would not believe the responses - what thugs they were, how common they were, everyone has them, snail magnets, invasive and so on. I was flabberghasted. In the UK, it is easy to forget the massive zone differences in the US and what is a choice, even rare and expensive plant for us, is just a common old everyday bore in California (where, it seems, everyone is a rose grower and the only perennials they have are a few daylilies) no, I am being a bit mean, but you get the picture?

forgot to mention - for many years, the only reliably hardy agapanthus was the seed raised strain of Headbourne Hybrids (which have, like Pacific Giants delphs, gone off the boil a bit lately). However, it may be worth attempting to grow some from seed as it does give them a chance to become habituated to your zone. I don't like pushing zones because I am a lazy and somewhat negligent gardener (too many enthusiams all competing for limited attention) so if it fails to thrive, I don't try again (well maybe once or twice).

I am a lazy gardener, but I never mind pushing zones. There is no exact science of zones, so how am I to know unless I try. We don't water, feed or mulch our gardens. We do top-dress with compost heavily, which allows for heaps of neglect.
My brother-in-law lives in California and complains about how agapanthus is a self-seeding menace. He does it to tease me.
But, on the other hand, I make a huge deal about the tulips every spring, because they are expensive and must be pre-chilled in California.

Size is an issue with me so I managed to get A. Peter Pan in a trade this spring. I potted it up and it's outside for the summer, among several other pots of flowers. I plan on trying to over winter it in an unheated garage this year. I have had success over wintering a Star Jasmine in this garage for several years. It gets pretty cold in the winter, but generally never freezes - unless we have one of those very, very cold winters, say down to minus 10 or more, which we haven't had in years. Then, I may have to move both plants inside for a while.

I'll post next spring and give you my results - yah or nay!
LInda

Santa Rosa Gardens is running a clearance sale, and I noticed that they too had Agapanthus 'Blue Yonder' marked down - so I decided to buy a couple more and experiment with them. :) I will try overwintering one in a pot in my garage and try the others in various spots in the yard. Maybe sheltering will make a difference in survival.

I resurrected this thread to update info on my potted Peter Pan Agapanthus. As soon as the weather warmed up, I brought it out from the unheated garage window and watered it. Most of the leaves were still green and looked healthy. A few had turned completely brown and I removed them. I did not water it at all during the winter while it was in the unheated garage.

It started to grow some new foliage and soon had buds coming among the leaves. The first flower heads have opened and I love the color. I will have to repot it to the next size up pot and plan on doing that as soon as the bloom is finished.

Linda

Congratulations on getting your agapanthus to bloom, Linda. We tend to take them for granted in SoCal where they can remain in the ground year-round.

As a side story about their toughness, I have a little tale. I was repotting a variegated agapanthus (large-leafed type) and had removed all of the potting mix. But then I realized that I didn't have any more bags of potting mix. So I placed the bare-rooted agapanthus in the pot and... eventually... experimented with how tough it was by not potting it for 7 months. Ocasionally I would sprinkle the roots with water. The dang thing never even wilted! TOUGH plant.

I wonder if they could be dug up and carried over bare-root style in cold climates where they need to be brought in.

Sorry about your experience, Campanula UK. I had the same experience and used to comment on the Antique Rose forum. Don't know about now, but back then they were overrun with a pack mentality, unhelpful and rude.

Is A. ‘blue yonder’ a smallish type of Agapathus ?

Yes, they are smaller in general. I m in Montreal and not sure what to do to have them return next spring, mulch them or bring them inside

I'd treat them like you do dahlias. Dig the roots and bring them inside in a cool, dark, place. Put them in a brown bag and check on them from time to time. Hopefully, they won't rot. Or, if you have an attached garage, you could leave them in the pot (assuming they are potted up), and put them in the garage. It probably depends on how cold your winter is. And these days, with climate change, we never know what kind of winter we are going to have. I didn't dig out a dahlia tuber that I had planted last year and surprise! It came up in the spring and is going to bloom soon. I've only had that happen one other time since I've been gardening.

Pina24, I'd bring it indoors in Montreal. I do that with my pot of Baby Pete, which I treat like a houseplant that goes out for the summer. It stays green all winter in the house. I'm in NY state, USDA zone 5, and they're uncommon here.

Thank you Eddie, I was told to
Leave in the garage and not give any water. Better to treat as a houseplant you’re saying..

Sorry meant to write Edie

So, it's been 11 years since this was posted. I'd like to think someone has something to report about growing this in zone 5. I found this thread because I fell in love with agapanthus in South Africa and I just fell in love! I would love a variety that can withstand NJ winters.

Hi, since then, i grow them outdours, in Montreal, ZONE 5, they come back every year, i covered them with straw and a thick frost coverI. Its been 4 years!

good luck

Some new hardy Agapanthus are slowly coming on the market. I (Z5) have a hardy white one which returns and blooms every year.