[Breezy]

Question if you would consider - best tonic for a mature griselinia hedge on the road ditch as it was planted eight years ago and has had little attention since. The hedge is a wind break fro my exposd garden so needs to be mantained and am starting off this year with renewed good intentions. Wondered as have a load of well rotted farm yard manure here if I gingerly put some on top of the ditch between the plants but not in contact it should seep down in time and nourish the roots and feed the soil?
Is that a plan, is it the best tonic or are there more appropriate?
Thanks in advance.

[Greengage]

“A good plan is like a road map: it shows the final destination and usually the best way to get there.”
Remember when Noah built the Ark it was not raining when he started so plan.

[tippben]

Griselinia littoralis is a bit dodgy in the UK and Ireland. Loads died, or were severely damaged by the severe cold a few years ago. We're basically trying to grow them near the limit of their range.

Your plan is good. A light mulch (2" deep? Don't know the height and width of hedge!) just outside the leaves, all along the line of the hedge will be taken down, and encourage the roots to spread further. You could use compost instead, but it's better to mulch little and often than dump loads on at once. definitely try to avoid any getting actually inside the hedge. You are right, it can encourage pests and diseases. You can also make "liquid manure" by putting a hessian sack full in to a bin full of water (remember to tie the neck of the sack tight and to leave lots of cord hanging over to fish it out. Some idiot forgot to do that once...) Then you can apply that with a watering can, about once a month. Any foliar feed, like liquid seaweed will also help.

The best thing though is autumn. Gather loads of fallen leaves and put them inside the hedge. Try to get them a good 6" deep. Don't worry about touching stems etc. you want a good thick carpet. They will help protect against frost damage to the roots, contain beneficial symbiotic fungi, and rot down to leaf mould. That way, you are mimicking a forest floor. Good luck!