We LOVE chive blossoms! They taste like mild chives and they look so pretty.
If the blossoms haven't fully opened when you get them home put them in a small glass with 1" of water. If you don't want them to open,put them in the fridge without water.
Once the blossoms have opened you need to use them within 2 days or they will dry out.
Here's how I harvest them: Hold the stalk in one hand and grip the head right below the blossoms by the dark red papery membrane that covered the bud. With the other hand grab the blossoms and pull. It's fine to use the tiny green stalks as well as the unopened flowers but don't uses the papery membrane. If the flowers have started to turn red, they are drying out and I would NOT use them.
Here's a photo of a small container of flowers that I put in the fridge to extend their life by a few days. You can see the tiny stems and unopened flowers. On the right are the stalks. The stalks are NOT edible (they're not chives) and will go on the compost pile:
Here are some of the ways I use the flowers:
sprinkle on green salads
press into deviled eggs
stir into mayonnaise
make a dip using quark & yogurt
preserve in EVOO or vinegar
blend into butter and then freeze (add chives, too)
sauteed mushrooms with thyme and chive blossoms
stir into mashed potatoes or sprinkle on baked potatoes
stir into cream sauce used for pasta