Question
I planted a 1 gal spanish lavendar plant last fall.  It grew like gang busters for a year - outgrowing the spot I selected for it.  It also bloomed on 3 separate occasions and I harvested some gorgeous bouquets of lavendar.  Then, suddenly, it began to turn brown and died so quickly, I could hardly believe it.  I live in zone 9

Answer
Hi Toni,
Thanx for your question.  Spanish lavender (Lavandula stoechas) is hardy to Zone 8 so your zone isn't the problem.  It requires hot summer for best fragrance and a somewhat alkaline soil but with plenty of organic nutrients.  Water well but don't let water sit in the pot or it will rot the roots.  Make sure the pot is free draining.  This plant is native to dry, warm areas of Spain and Portugal.  Did you pull the plant out of the pot to see how the roots were?  Fusarium root rot and leaf spot are typical diseases but not really that common either.  I hope this helps.
Tom