I just inherited a grouping of ginkgo  in a oval pot the trunks range between 1" to 1/2" . The outer layer of soil is just sand an 1 1/2 wide around the entire oval pot.
I have a second ginkgo plant that is twin trunked.
My question now. Some of my literature says to repot in the summer others literature says Spring I want to combine the two ginkgos to have a major landscape planting. I want to place both into a pot is 23 long and 18 wide. What time is best for the ginkgo plants Spring or Summer
Both are ok but spring is surely better. Also it depends where you are I guess. They need more care during summer repotting if very hot - am I right here actually or is it only my concern??
I personally have only expirience with spring repotting and had success with it (including Ginko). I think summer is the most difficult time for repotting in general and I haven’t meet someone who done it successfully in June or July. If in doubt use the spring.
A commercial nuseryman told me once that most plants can be transplanted at any time as long as the roots are not frozen. However, the chance of success are higher if the plant is just about to push growth.
I’m not sure about Ginko, but the roots are very fleshy, so maybe after summer dormancy when the tree puts on vascular and root growth? Also, the vigour of the tree should be considered. For the best chance of success, I would be looking at repotting in the spring as the buds swell.
the nurseryman is right, but not for bonsai. Putting a container stock into the ground is totally different from manipulate the roots to fit into a small container with limited buffering capacity in terms e.g. temperature, moisture, microbes and others. slip potting as an intermedeate step to the ground is also not comparable with bonsai repotting.
We ask our trees to do extodinary things for us, and in return we have to do everything we can to stack the odds in their favour.
I would ask about the health of the trees, what area you are in, what kind of after care you can provide, and your experience with the species.
Like @CoffeeCherry said, spring is typically better, because temps aren’t so extreme. So if you’re in a relatively hot area, it’s probably better to wait a few months for spring, unless the trees are super healthy, or you’re able to provide amazing care afterwards.
Even then, making a group planting will likely require root work. I would think waiting until spring only increases your chances of success.