First, make sure you re-pot at the optimum time of year.
I re-pot in late Winter/early Spring in my area.

Second, Yes, you want to get rid of as much of the existing soil as possible.
The first transition will typically be the most stressful...for you and the plant ;-)

Josh

Unfortunately a number of these plants need to be re-potted asap. They are recent purchases, and cannot overwinter in the small containers.

So September is the optimum time, for them!

Even if they're THAT root bound, I'd work toward having timing on my side by cutting the bottom of the roots off or tearing off any roots circling the bottom of the pot, then loosening some of the remaining roots at the sides of the pot and potting up into a slightly larger container, using soil similar to what they're in, leaving the full repots until spring - late Apr or early May for you. Your plants/your call - that's just what I've learned after thousands of conifer repots.

Best luck always.

Al

Thanks, Al, for your always excellent advice -- greatly appreciated!

I will make up a blend of Black Gold potting soil with some bark fines and pumice added, tease out and/or cut encircling roots and use somewhat larger pots, if need be, and wait until mid-spring to pot them into the gritty mix.

Here is the mix used by the Oregon grower of the plants:

"I use 90-95% bark as the base with 5-10% pumice and a few other nutritional elements. It may be on the dry side for your climate."

Does not seem too far removed from the gritty mix after all!

I can imagine adding a small amount of 8822 and grit to this for re-potting now, or do you think I should use his formula until spring? If so, what might I add to increase water retention a bit?

Yep, wait for the best time to do the re-potting :-)

That mix you mention is quite removed from the Gritty Mix, which is approximately 30% bark.
It is much closer to 5-1-1.

Josh

Yes, it certainly seems much closer to 5:1:1, but he is not using anything such as peat moss to increase water retention.

That is why I was considering adding some 8822 and grit into the mix, together with bark and pumice. But I am wondering about percentages?

BTW, I am planning on growing a number of his plants in containers for a long time.

I don't think you'll need to add any moisture retentive ingredient for this temporary potting up.

For long term plantings, you really can't get much better than the Gritty Mix.

Here's a Picea abies 'Little Gem' that I transferred this Spring to a gritty mix with red lava rock.
(incidentally, I sunburned it pretty bad and now have it on the northeast side of my house in shade).

Since the optimal time for re-potting where I live is early May, and a number of these new plants are somewhat rootbound, seems like I will have to do two re-pots for those that will be living in containers.

I was trying to make the process easier, but probably the plants will do better in similar soil to which they were grown for the winter and early spring, and then into the gritty mix in May.

Yes, it will be more work for you....but better for the conifers in the long run.

Josh

OK -- I fully accept the situation.

So even in the dry, low humidity, intense sunlight climate of northern NM (elevation of 7000 feet), do you recommend using the same mix as the grower, and feeding weekly with FP 9-3-6 through late autumn?

I can mostly keep the plants protected from afternoon sun.

Sounds good to me.
I fertilize every two weeks with the Conifers and Maples.
Al grows in a much colder climate than I do, so I'll defer to him on container-size
and how to winter these trees.

Josh