Can crypts like C. crispatula and C. undulata be planted in groups? It's my first try on a planted tank and I planted them in groups of three because it's easier to anchor in the substrate. Is that fine? TYVM!!!
Crypts are generally pretty hardy plants and you might be ok. However, planting them that close may result in the roots of one choking another. I've always aimed for a 2 inch radius between mine.
Do you mean planting separate species close together (no!)? Or a "potful" of each divided by a few inches per clump (yes!)? Be aware of "crypt melt" as they adjust to your tank. No problem if the roots are healthy, the leaves will regrow, just be patient.
I'm in tune with the 2" radius plan. That will give them plenty of room. If you start to get melt, immediately pinch of that leaf's stem at the base of the plant. Even if you pinch off all the leaves due to melt it may come back...been there done it.