Posted: 26/04/2016 at 07:46
first thought ...did you simply pull out the old lavendar and pop in replacements? If so this is likely to be the reason for slow growth
last autumn I replaced a lavendar hedge around my veg patch. The replacements are growing fast but I replaced and replenished the soil there.
I think you should have planted,them elsewhere or replaced the soil there.
All you can do now is feed although,,paradoxically, you don't really feed lavendar....they flower better and are hardier when grown hard.
thus I would use seaweed spray once a week for a few weeks but growth should still come soon anyway