If you're sealing these tiny jars in a chamber vacuum sealer, I've found the best way is to put them in upside-down. For some reason, they have a much higher seal failure-rate than the big jars if you put them in the normal way.
Other vacuum packed salad posts:
The Great Salad Experiment
Great Salad Experiment - Part 2
Spinach and green leaf lettuce experiment
Opening vacuum sealed jars
Lets vacuum seal a bunch of stuff
(includes putting salad vegetables in vacuum sealed bags)