An Event Permit is required to sell or distribute nursery products or floral items at a temporary location. One Event Permit equals one day (or any portion of a 24 hour period) of operation. If you are selling online prior to the event, you only need a license for the day(s) of product pick-up.
https://www.texasagriculture.gov/RegulatoryPrograms/PlantQuality/NurseryFloral.aspx