The junipers can just about dry out, but it's very subjective, because in the SW, it could mean the end of a little tree in a little pot (especially if the pot wasn't shaded), very quickly, whereas in the NE, you may get away with it for longer, in the summer or fall. There's a lot of in-betweens here, and you have to use your own judgment to decide. Obviously a good sized tree established in the ground can go for a very long time compared to a potted one, but it all depends on the tree, the pot, the sun, the soil....

Lucy, thank you for your advice. I was afraid that might be doing something basically wrong. Most bonsai areas that I have seen are partially shaded and have some protection from the weather/winds. Most patios and decks are not as well suited so we have to make adjustments.

I would fertilize them more frequently, especially the seedlings, at least once every month, although it can depend on the supplier instructions. As for the moss, I think it's a good measure to prevent total dryness during those 2/3 days in the summer, but keep an eye open for pests such as fungus and rotting, moss can trick you just like that. Don't bother pulling the moss away when you feed. Active transport systems of the roots for nutrients absortion isn't that quick so even if you feed on top of the moss it eventually will drain into the soil and disperse within it. If you use a moderate concentration of the fertilizer it's one more reason not to direct the fertilizer to the roots to prevent root burning. Oh, and avoid fertilizing them with the soil completely dry, water a bit first for the same reason.

Best health to your juniper and maples ;)

FP

FP-I will fertilize at least monthly as you suggest. Understand that it is better to fertilize more often with a weaker solution to avoid burning.
Thank you
Steve