Despite the numbers people are throwing at you, dayblooms are pretty decent drop and forget generators. You only really need to either move past them or expand them greatly once you want to get into terrasteel or duping. Just the dayblooms you get as quest rewards should be more than enough to progress through all the runes and magical seeds you need, they have been for me so far, I'm not even using the hydroangeas since they are a waste of space.
Check to make sure all your dayblooms are linked to the spreaders, they only have a ~5 block range and can become unlinked if you move a spreader after placing them. Also something a lot of people don't realize is you can conserve space by placing dayblooms on different levels directly next to each other, so make a checkerboard of dirt and place dayblooms on top and in the gaps, filling the space completely, there are no diminishing returns with a 1 block height difference.