Phillip did you plant lavender in the ground or in pots. Lavender is drought tolerant in the ground so it has a fine but extensive root system. It does likes a slightly alkaline soil and it needs to be well drained. L. augustifolia does best in zones 5-8. In zone 10 and above it grows best in the higher elevations. I live in zone 12a so they do not do well for me unless I provide afternoon shade in summer. I have most of mine in pots but I have had lavender multifida in the ground with afternoon shade. Instead I grow lavindins (crosses between l. augustifolia and l. intermedia ) that can handle heat better. Lavender multifida is an ornamental lavender that will bloom nearly nonstop for me and it is the only lavender for zone 10. In pots they do not get very big, but in the ground they become a very big mounding plant at least 3 ft in diameter and over 3 ft tall. It hates being rained on and the leaves will turn black and rot, and it does not need or like a lot of fertilizer. I only use slow release once a year. Lavender should be cut back once a year, but only cut soft wood. Cutting into old wood can kill the plant or make it take a very long time to come back. I usually cut it back around January when my rainy season starts. I try to wait until I see new shoots coming from the old wood and I prefer to cut back half the plant only. If it is going to rain for a week, I have not choice but to cut all of it off and hope for the best. Lavender should be cut back to make it look nicer otherwise over time the woody stems will take over and the top will look smaller. You would then have no choice but to cut it back harshly and it will take a long time to come back.
Happy gardening in Hawaii. Gardens are where people grow.