Answer: I'm not sure why the foliage is turning odd colors, but you're doing the right thing - remove the affected plant parts and feed lightly to encourage healthy new growth. You might try a light application of Miracle-Gro; it feeds through the foliage and through the roots.
For general reference, plant sea lavender in well-drained soil in full sun or, in hot climates, in a place with afternoon shade. Keep the soil moist but not soggy wet (a weekly deep soaking is better than frequent light sprinklings). Remove old foliage in spring, using bypass pruners to cut off the old stems. Apply a light application of organic fertilizer on top of the soil in early spring; follow package directions. Mulch around but not on top of the plants with 3 inches of organic compost in spring to help slow water evaporation.
Best wishes with your Sea lavender!
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