Tips and tricks

Write only on the white side of the label, the colored side is paper and will disappear over time.
Air dry bags mean that they are not dried in a special way. You can directly use them from the package. In areas with a high humidity, you could store the bags longer in an air tight bag or box with some silica grains.
Mark your location in a way that you remember. Be sure that this marking does not attract extra attention of curious people to check out what the marking indicates. Make therefore a good map in which you indicate the distance to three fixed points. Or you can use a (plastic) string that runs over the soil and attaches the bag label to another fixed point (e.g. a tree).
If you are going to dig up the bags, first try to locate all (or most) of them. Use your map for this.
If you found the label, do not pull it hard, as it might easily break. You can make the soil around the bag more loose by taking one big scoop of soil and than search for the bag in the soil.
8 cm is halfway the rope, so if you bury the tea bag, the soil level should be at the location where the rope is flattened/melted.
Put an alarm in your phone to remind you when to dig up the tea.
If you are unfamiliar with soil types: check the soil classification of FAO.