I am growing a small lavender hedge and over the last two season it has done very well, with the exception of the plants that share ground with a large root from a silver birch tree. These are really lagging behind. I assume this is due to the tree steal the water from them but when I brought the plants I was told not to water them except in drought conditions because the develop a deep root. What can I do to help these struggling plants?
I have a lavender bush, I water it when I do the rest of the garden if it's dry. It's doing well - it's in the border and I don't treat it any differently from the rest of the plants.