Around 15 years I would say. Give or take a few years.

J

All I know is the of all the green giants I planted (easily over 150 of them) they all seem to grow at different rates. I have some I planted around three years ago at around 20 inches high and some are now closing in on 5-6ft-while others are half that height. Some this year have already a foot or more of growth while other in the same area might have 6 inches. I have one I planted by itself on the opposite end of the property (near wetlands) around 4 years ago and it has filled out more but height wise has probably only grown 2ft or so. Granted the ones I have are not al from the same batch- but like growth- the bronzing on them from winter varies all over the place too- some show no browning while others alot more.

How fast they will grow will depend on location/climate, soil conditions, watering attention and how carefully they were planted to begin with. Ideally, after establishment (2-3 growing seasons), one can expect 3-5' per year.

I wouldn't expect 1' trees to show much significant or rapid growth to begin with :-) Give 'em three years or so.