I doubt they'll survive -3 degrees--zone 6 here. In the US, they're hardy only to zone 7 at best. Also, I've heard that many of our hardy ornamental grasses don't flower in the UK because the summers are too cool and cloudy. I suggest you try one of the Miscanthus grasses, or if you want something very tall, Erianthus ravennae, Ravenna grass--but keep in mind that cutting back 22 Ravenna grasses in spring or even 22 Miscanthus--is quite a job.

That -3 is probably Celsius (about 27F), particularly since the poster lives in Ireland and guesses a hardiness zone of 8 or 9.

The cortaderia should be fine for you. They grow easily in both zones 8 and 9...sometimes too good in zone 9 :-) And if they bloom easily in my zone 8, which is the closest climate to the UK of anywhere here in the states and also enjoys cool cloudy summers, they should do the same for you. In fact, about the only grasses that don't bloom well in my area are some of the Pennisetums.

I assume the -3 is Celsius since the post is coming from Ireland.

Well I have sort of logged the temp every day since they were planted and it was only -3(celcius) during one night, the rest were -1 and very seldom -2 up until now were the temp has risen to 5 to 6 degrees, I really love seeing this plant standing tall and proud in other gardens close to my home and have become obsessed about pampas grass!

Also can anyone tell me if they do grow well in zone 8/9 are they low maintenance?

They are an invasive nuisance here and the California Native Plant Society would be glad for your assistance in digging one out. If you have ever dug one out you would not EVER plant another. Along the coast in December of 1990 the temperature reached 14 degrees Fahrenheit for four nights in a row and all the Pampas grass survived. Even though your plants were not mature they should survive -3C. Al

All I can say is that I hope you have a landscape crew to cut these back every year for the rest of your life. I will never plant another pampas again for that reason- I have to cut the thing back myself and haul it off and it usually takes me a very full day to do it.
Of course, you could always burn them each year-lots of people do that but it's still a great deal of work.
I can't burn mine, it's too close to the house.

Since pampas grass is evergreen, especially in the OP's climate, it doesn't require cutting back annually. There are many plantings of it my area that rarely get cut back. In fact, it tends to look better and with a more natural fountaining habit if left untrimmed. For that reason, plus the fact that most grasses are very drought tolerant and do not require any fertilization, it IS considered very low maintenance.

If the grass does need attention - removing old, tattered plumes, the occasional trimming or very infrequent dividing - be sure to wear gloves and protective clothing. The blades are very sharp and can cut easily.

I am growing a dwarf pampas that does not make viable seed and is not invasive. It only gets to about four feet high, but has ths same flower stalk, just small scale. Al

I hated my pampas grass.... I divorced it , then I murdered it. It was him or me. I do not even want to talk about it.... The memory is still to fresh.