First and foremost we want you to be comfortable! That said, please dress appropriately for a wedding. We want you to have memorable photos while you're having fun.
Santa Barbara in March is typically mild climate. Expect low 60s during the day and slightly colder in the evenings with a gentle breeze and plenty of sun.
The wedding will likely take place outdoors on a lovely lawn on a sunny day. During the wedding you will be facing east away from the sun. Dinner will be on a patio with space heaters.
If you plan on exploring Santa Barbara outside of the wedding, then we recommend you also pack a swimsuit, hat, sunscreen, and sandals.