I planted a Lilac bush (Agnes Smith variety) in April this year, but the soil in our garden is quite clay based, so after having drainage problems with a buddleia and forsythia I had also planted, I dug in several bags of horticultural grit back in May. The buddleia and forsythia have now grown like crazy, but the lilac hasn't grown at all since it finished flowering, and in the last month or so the leaves have curled. Some of the top leaves have also developed brown patches. I have watered the plant a little every few days over the last few weeks whilst it has been dry and hot, but not too much. Can anyone advise as to what the problem could be?