The pachysandra is very mature and hardy
I would think it would be fine. Many plants can tolerate being sheared for rejuvenation.
https://www.gardeningknowhow.com/ornamental/groundcover/pachysandra/pachysandra-ground-cover.htm
Pots are 2 1/2 inches
Plant them 6 to 12 inches apart. These articles should help calculate.
https://www.gardeningknowhow.com/garden-how-to/info/plants-per-square-foot.htm
https://www.gardeningknowhow.com/ornamental/groundcover/pachysandra/pachysandra-ground-cover.htm
d, will it get the fungus also? I have sprayed the bed in the past with an antifungal called Serenade
Usually planting a different plant in an old space is not a problem. It's when we replant the same type of plant that reinfection occurs. Here is more:
https://www.gardeningknowhow.com/plant-problems/environmental/planting-in-old-spaces.htm
I have shale ground that prevents me from placing 6 inch edging. If I border my pachysandra garden with 12 inch wide slate slabs, will that prevent the pachysandra from spreading beyond the garden area?
This article will help you:
https://www.gardeningknowhow.com/ornamental/groundcover/pachysandra/pachysandra-weed-control.htm
What maintenance is needed each Spring for pachysandra? any pruning or trimming back or leave it alone?
If your pachysandra seems to need some pruning, it's fine to cut it back, but no more than half its height. If you think it needs some food, use a balanced 10-10-10 fertilizer. Here's an article about that:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/what-is-balanced-fertilizer.htm\
https://www.gardeningknowhow.com/ornamental/groundcover/pachysandra/pachysandra-ground-cover.htm
I need to know what is safe for my pachysandra to treat this leaf blight
I'm afraid that it won't be near strong enough to take care of this issue. Applying Neem oil while it is sunny will kill your plants, anyway. It will be better to turn to copper based fungicides.
https://www.gardeningknowhow.com/garden-how-to/info/what-is-copper-fungicide.htm
We have a bunch of pachysandra in our backyard, which we love. Over the past couple of years, we've noticed a growing bald patch in the middle of what used to be beautiful, healthy ground cover. It gets sufficient water; it is a shaded area (especially when trees are in leaf). The only reason I can come up with is that this bald patch is on/around the root system of a very old maple tree. Could the tree be starving the pachysandra of nutrients? Would it help if we add new dirt, or spread mulch and/or compost? I've attached two photos below, as follows: Photo #1: bald patch beneath maple tree Photo #2: healthy pachysandra immediately adjacent to bald spot Thank you!
I wouldn't think it was the root system because trees have feeder roots several feet from the tree and all around. Check the plants next to the bald spot for tan areas. There may be a fungal disease that is causing it to die out.
Here is more:
https://www.gardeningknowhow.com/ornamental/groundcover/pachysandra/pachysandra-volutella-blight.htm
https://www.gardeningknowhow.com/ornamental/groundcover/pachysandra/pachysandra-ground-cover.htm