I have 3 crepe myrtles and they're all doing this. I've never seen this happen before.
Crepe Myrtle is deciduous. The leaves begin turning colors, curling and falling in late September. This is normal.
I live in zone 7 and am not sure if I should be cutting my dwarf crepe myrtles back or just leave the alone. If I am supposed to cut back, do I do it now or wait until spring?
These articles will help you:
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/pruning-crepe-myrtle-trees.htm
When to prune crepe myrtles in Georgia?
These articles will help with pruning your crepe myrtle trees: https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/best-crepe-myrtle-pruning-time-when-to-prune-crepe-myrtle.htm
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/pruning-crepe-myrtle-trees.htm
So-called professionals pruned our two Crepe Myrtles. It appears to be that they just deadheaded, but did not actually do appropriate pruning. It appears that all of the long branches are still there, and I see quite small projections (large twig sized ends) at the ends of those branches. I did not measure the diameter of those end-points. The trees appear to be quite mature - perhaps they are about 12' in height.
These articles will help you: https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/best-crepe-myrtle-pruning-time-when-to-prune-crepe-myrtle.htm and https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/pruning-crepe-myrtle-trees.htm
How deep are the roots of a 5 year old crepe myrtle tree?
Generally, the root system will extend at least as far as the canopy of the tree (if unpruned), but some may have a root system up to three times as wide as the canopy, or drip line of the tree. However, with crepe mytle trees, there's no need to worry much about invasive roots, as their root systems are not aggressive, meaning they are not strong enough to pose any major threat to nearby structures or plants.
When trimming back a Crepe Myrtle tree that has been trimmed before, do you have to cut the limb above the "knot" area that has established from previous trimmings, or can you cut back below the "knot" area to keep the tree from growing taller each year?
You should be able to, but without knowing the exact shape of the tree, we would not be able to tell you how this would affect the future shape of the tree. It would be worth it to have a landscaper who is experienced with crepe myrtles come and look to make sure that the tree will retain a pleasing shape if this sort of pruning is done. This article should help you with that: https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/pruning-crepe-myrtle-trees.htm
A large number of our crepe myrtle trees have a mossy growth on them, which is similar to that which grows on oak trees. It is a somewhat scalely green/gray colored growth. It looks similar to that mossy growth that appears on rocks and some small patches of bare ground occasionally. It has increased in amount and the number of trees that it is growing. Is it harmful? How can we rid our trees of this growth?
It is lichen, which is harmless to the tree. Here is more information: https://www.gardeningknowhow.com/ornamental/fungus-lichen/treatment-tree-lichen.htm