Memory Jars is an exploration of living in the moment, even when you find you have the ability to bottle the moment and save it forever.

Freda and Gran spend a "hot, sweet, sticky July day" picking (and eating) blueberries. Freda is so enraptured with the experience of eating the delicious berries that "taste like sweet sunshine" that she tries to eat them all, keeping the good times going forever. When she falls to the floor in tears when she can’t, Gran tells Freda not to get upset. They can put the berries in a jar and save them by making jam that they can enjoy all year. After all, blueberry jam was Freda’s grandfather’s favorite.

Taking the jam jar her Gran gives her, Freda has an idea. Over the next several pages, readers see her collecting all the marvelous things she wants to save and remember forever. Somehow, whatever goes in the jar is, literally, preserved. Gran’s freshly baked chocolate cookies stay warm, rocket pops shared with friends don’t melt and poppies don’t wilt. Freda even puts her friend Jack in a jar so that he won’t have to move to Arizona at the end of the summer. Jack, now tiny, cheerfully waves up at Freda from his jar. Freda jars her neighbor’s beautiful singing, vibrant rainbows, and a cloud that look like a unicorn so that it would, "never be pushed back into a mushy nothing by the wind." Finally, Freda asks Gran to get in a jar and she agrees, leaving Freda in a very silent, kind of grey world.

Hungry from her efforts at preservation, Freda pulls a jar of homemade blueberry jam from the shelf and spreads it on her toast. Taking a bite, happy memories come flooding back to her and she begins to understand – some memories, like the berries that go into jam, can be preserved, but the best ones are experienced as they come, and go.