We have very chalky, alkaline, very free draining soil. We planted a Laburnam 2 years ago, it had quite a few flowers on it last year (unexpected!) but this year - NONE! And yet it has grown really well??? The Lilac was planted 3 years ago, bought from a nursery when it was quite 'poorly'! It picked up very slowly over the last 2 years but this year it is lovely and green, lots of leaves, about 6 feet tall, but - NO BLOOMS! What is wrong?