You should enter the Plantentuin via the Empress Charlotte entrance (accessible from 38 Nieuwelaan 1860 Meise). There is free parking on Nieuwelaan. From the entrance walk straight ahead and you will find the castle at the end of the alley. If you have mobility issues let us know and we can arrange for you to be able to drive all the way to the castle for drop off.
We will send you the ticket to be shown at the entrance a few days before the event. The ticket will get you access for free to the Plantentuin. You will be able to access it from 10 am onwards on the 26th of August. Follow the "View" link for the Plantentuin website containing a map of the site and information on all the things to do there.
I am not sure how Uber is running in Meise. Here is the phone number of a taxi company you can contact if needed: (+32) 2 268 00 00