You don't say where you live but if they have flowered cut the old ones off if it is mild they should flower again give them a potash feed because there in pots
The most important thing for lavender is drainage. A mix of 50/50 grit and compost is best a feed every couple of months in spring and summer will see it bloom well. Once the flowers are over trim it back to new growth (don't cut into old wood) and it should be fine.
I find my lavender doesn't need much encouragement, enough sun & warmth, cutting off spent flowers and it keeps trying to flower. Mine is in free draining compost (lots of perlite), in a pot on a south facing patio. Even now at the end of autumn it is still tring to flower.
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The most important thing for lavender is drainage. A mix of 50/50 grit and compost is best a feed every couple of months in spring and summer will see it bloom well. Once the flowers are over trim it back to new growth (don't cut into old wood) and it should be fine.
I find my lavender doesn't need much encouragement, enough sun & warmth, cutting off spent flowers and it keeps trying to flower. Mine is in free draining compost (lots of perlite), in a pot on a south facing patio. Even now at the end of autumn it is still tring to flower.
If you do feed, feed sparingly with low Nitrogen feed.