I'd roughly guess at least 30 ft. But doubt you'll be on the same property by the time they get close to each other. Me, I wouldn't have an issue planting them alittle closer -- my green giant arbs are only 7 ft apart....

Thanks. I should have mentioned that the White Spruce and Norway Spruce will be planted in separate parts of the yard, screening two different objects. Are you saying they grow taller first, and then fill out years later?

where are you ..

how big are you starting with ...

spacing is a personal preference.. mostly depending on how many decades you want to wait.. to hide you goal ...

as trees.. they will never stop growing ... so when you say you want them to hit their width potential... but stop when they barely touch .. you cant come up with that projection ...

as an e.g. .. here is picea glauca potential .. should you live so long ...

https://duckduckgo.com/?q=picea+glauca+forest&t=ffcm&iar=images&iax=images&ia=images

there may be better options to achieve your goal ... but we will need location ... and perhaps a pic or 3... to offer such ..

welcome to the forums ....

ken

I'm getting the plain White Spruce, not Black Hills. This is for my dad's yard. We're in Syracuse. I've just moved in with him. He has mid-stage dementia, and can no longer live alone. His yard is a complete mess, and I want to strategically plant some evergreens for more privacy. I have no idea what his soil is like. Is it too late to plant now?

Yes, the "plain" white spruce is much better than the Black Hills, IMO. Got a pic of some mature, "plain" white spruces:

Timing depends on several variables. In your zone 5B I wouldn't plant container stock if you're goal is to plant and leave it be permantantly. Odds are container stock needs root work. This time of year roots will not regenerate. The fall rooting from existing roots is done at this point. Roots will not be growing this time of year unless temps are higher than average and thats certainly not the case. My soil, your soil will likely freeze a few inches with the ensuing temps. With all that said you can still plant if the ground is not frozen and still be totally fine. However it will depend on exposure and type of winter you have. If you're exposed to prevailing winter winds and its a rough winter those needles will burn burn burn and the plant will struggle going into next year.

Best bet is to plant in spring. You can tear through those roots if needed and they will regenerate that time of year. In fact I see them do this well through the summer. For b&b stock you really can plant anytime the grounds not frozen. Again make a judgement call based on exposure.

Kudos to you for stepping in to support father.