can not sort table

Hi. I've made a plant database for designing edible landscapes however I can't figure out how to reorder the plants in one of the tables in the form called "3)What plants could grow? The Microclimate" For example: when I click the "sort" (ZA) icon the sort order dialogue pops up and I select the "Height" field from the drop down menu and click "OK" ... nothing happens. I would expect the order to change unless they were already sorted that way (which they are not). The other tables on the form are working as they

Here is a link to the database so you can have a look.