Posted: 02/08/2014 at 14:19
I'd take out the yellow one. I fear it may be beyond help but it's worth a try potting it up in something well drained. Also, if those are both ordinary lilacs they're far too close together and to the fence to allow for growth.
I think you should always pick your plants to suit soil and aspect or you'll be forever disappointed.
I'd love some of those Japanese acers, but I have dry alkaline soil and a windy garden so I go and admire them somewhere else