Howdy!
I have a mugo pine in the ground, which I transplanted in late winter / early spring.
I don't really know the answer to your question, since I've always assumed it best
to do root-work / re-potting of conifers in spring (before budbreak) or in autumn (after
the first rains have begun to fall).

However, when I did a search on "mugo pine" and "mugo pine repot," I read that mugo pines
prefer to be "worked on" (foliage, at least) from the middle of June, on through summer.

I hope someone chimes in with more specific advice!

Josh

It doesn't sound like you're doing anything too drastic so about anytime in summer shouldn't be a problem. I did most of my repotting of everything beginning in the spring, that way most didn't need any special care during a few weeks of recovery.

I did avoid doing much from about mid July to the end of August due to heat.

Bob

The heat is the real trick to re-potting this tree. Being an oddball and preferring root-work in summer I guess I just need to look for a cooler week and do it. I know every location is different, I was just looking for a guideline other than "summer." My concern is that July and August are our hottest months and we have already seen upper 90's with index into the 100's. I will of course move it to a shadier area after the re-pot (re-box) and just watch it. I don't typically get nervous working cheap material but this is a pine and I have been watching it grow for several months now.

Now is a good time to transplant but not to much longer.
I believe Mugo is one of the trees V. Wood said he plants around the 4th of July.
Paul

A bunch of us would always get together after the cold house was opened up and spend a weekend repotting/reworking trees. About the only trees not worked were Azalieas or ones that were looking weak.

There are those cool wet spring days when it's impossible to kill a tree.

Bob

So I guess similar to Spring, you try to do as much early in the season as possible? I will be building the flat for it over the next few days so it should be re-potted before next weekend. I am interested to see how it has fared thus far.

But, as you said in your OP, you're mostly just going to slip-pot it so that's no big deal anytime of the year. I lived in Pa so the idea was to get the major work done in early spring in order to get the most out of the growing season. You have the rest of the season to do wiring, pruning and all of the other work.

Weather and micro-climate changes make everyones spring and summer different. Were the trees are in your yard may be in a different little 'zone' from your friend down the block. The same way a greenhouse has different 'sweet-spots' for different plants.

Hell...I just moved one Ficus and an Arilia 15' in my courtyard and they got upset over that!!!

Bob