If you know you're going to need to buy flowers then sign up as far in advance as you can, practically, to a couple of flower delivery sites. Often if you've been signed up for a while and don't make a purchase - or additional purchase if you've made one - then the company will try to entice you back via deals. I've been offered free shipping, discounts and so on using this method.
That's a very useful advice. Everyone I know who ever ordered flowers through websites before never signed up beforehand and they had to pay hundreds including the delivery service. I must say that these people are including my husband and other family members. None of us ever really thought about signing up earlier before making a purchase because we didn't think it would ever be cheaper unless there was a promotion for everybody.