Normal seeds and sprouts won't work to unlock these clouds. In this case you'll need Grimm Seeds and Sampling.
To obtain Grimm Seeds, you can try one of these:
- Tap on Graves
- Dragon Egg Chests/Nest Vaults harvested from Grimm Trees
- Open Grimm Chests
- Spawns from Grimm Trees
Merging these seeds will create the Grimm Saplings needed to unlock the other cloud.