When is the best day to plant flowers?

So many people getting their homes ready for market. When can they start planting those flowers?

My baskets were so big last year, they actually pulled the hooks right out and fell down. Lesson learned.

Seattle temperatures are mild, but there was frost on the cars this morning. I figure when I see the yellow heads of the daffodils, it's OK to plant other things at that point.

We used to say Mother's Day back in the Northeast, but seems to me in Seattle we could plant earlier than that.

I want to plant pink begonia. Anyone have an answer for that in the Northwest?