Appropriate grades or age groups:
Grades 2-5

Estimated time to complete this project:
Several hours to overnight.

Materials:
tall jars
celery stalks (or flowers such as white carnations or daisies)
food coloring
knife (adult use only!)

Instructions:
Trim ends of celery stalks to the same length (about 8 or 9 inches, including the top leaves). Cutting at an angle seems to work the best.

Put one stalk in each jar/vase, add water and plenty of food coloring.

Note the time you started and remove a stalk at 2 hours, 4 hours, 6 hours and overnight.

Cut the stalks to see how much colored water has been absorbed, i.e., how far up the stalk the water traveled.

(If you use flowers, you obviously can't cut the stems this way, and it will take a few days before you can see some of the color appear in the petals. Celery stalks won't be extremely attractive after a long day or two without water, and these flowers add a nice touch to the display.)

Other comments or suggestions:
There are several excellent sites on the Web if you search under "capillary action" which will give you ideas for charts or pictures to accompany the project.

And I don't think it influenced the judges to award my daughter Third Place last year for this project when she gave the flowers from her display to them and to her teacher! :-)