By Judithj
Scottish Borders,
United Kingdom 
I have three rowan trees, not sure how old, but fairly small. They are all covered with grey lichen which according to the RHS website is non parasitic but does indicate they are not very vigorous. Would giving them a feed of Growmore around the main trunk be any good at all - or how else does one improve the 'vigour'???
14 Jun, 2010
Answers
When you consider that the rowan grows fine on scottish hillsides with no help or assistance I would think the lack of vigour is not from the lichen but from poor soil. Which varieties of rowan do you have?
15 Jun, 2010
Lichen is an excellent indicator of clean air. I don't know about it being a lack of vigour though.
DON'T apply fertiliser to the trunk as it may burn.
Apply fertiliser at 1/2 strength around roots as far as the canopy spread. Also you can spray the leaves with 1/4 strength feed monthly during the growing season.Spike with garden fork around tree to improve drainage and to allow air to the roots. Water trees regularly. When you think you've watered sufficently, water them again. Try not to let the soil dry out below 2" deep.
I hope this helps.
14 Jun, 2010