In late April, we are eager to get color in our landscape but we have many annual flowers in our greenhouses and a few outdoors ready for sale that should not be put out in the ground immediately.
However, perennials in the yard are ready to be planted.
Also potted flowering bulbs of daffodils and hyacinth can be put in a garden location now. Fertilize while the leaves are green and they will bloom again next spring.
The chart pictured below gives you the general hardiness guidelines for some common annual flowers. This chart was adapted from: http://www.walterreeves.com/landscaping/flowers-cold-hardiness/