I've grown a few holly bushes from very small plants. They seem happy and healthy but have grown slowly during the past few years - the biggest one is still only about 30cm tall.
How big should I let them get before planting them into the ground?
Plant them in the ground now. They are really forest trees.
Holly always grows quite slowly, as pansy face suggests its ok to plant out now. They are tough just make sure they get watered.
Okay, I'll plant them out. When do hollies start to grow berries?!
Some don't - it depends on the variety - but it also depends on whether there are others around for pollination.
As the others have said, once you get them established in the ground, they'll grow on well and make big trees eventually. You can clip or trim them as you wish though. They're tough as old boots
Hollies are funny plants in that there are male plants and female plants. Only the female plants have berries but, in the wacky world of hollies, they often have male names and the males have female names. So Golden King is female and has berries. Golden Queen is male and has none.
Holly has been my favourite plant since one of them started growing in my mum's garden when I was a child. I persuaded her to let it grow and now it's 10ft tall and produces berries