The reason some spots don't allow planting is the idea that they have too much or too little resources for your plant (e.g. too much water and it'll drown, too little and it will die of dehydration)

The plant should bud, then when you hit next stage it will flower and give you dna, when you hit next stage again it will give you seeds to plant (but they have a limited lifespan so you might want to pick out where you want to plant in advance). If you click the upgrade you will see a tree you can spend your dna points on.

Unless of course you mean you can't see any UI, in which case ignore what I said, maybe try a different build? because that'd definitely be a bug.

I updated the game page with some more info to try and make it clearer if you want to have another go :)