Can I plant my yukka outside (New Zealand location)?

My yukka is about 8ft tall and can no longer be accommodated in our room without the leaves being forced to bend. We live in Wellington New Zealand, and my garden is north facing (thats the equivalent of south facing for those of you in the northern hemisphere). So we have all day sun. I am sure I have seen yukkas growing in other people's gardens - some of them much taller than their houses. Freddie's (thats the yukka) trunk is just 3 ft high, the rest are leaves. I rescued him from someone who could no longer look after him. I repotted him straight away, and in the last 2 months he has grown 4 new leaves and his other foliage has really perked up. So it would be a shame to plonk him outside and lose him to the cold nights. Appreciate any suggestions and advice from other new zealanders! Cheers.