Garden Q&A: Our griselinea hedge is dying. What should we do?

Whether you're a gardening beginner or expert, Irish Examiner columnist Peter Dowdall has the answer to your questions  

Dieback in large section of the perimeter griselinia hedge.

Question

We have a griselinia perimeter hedge that is 39 years old. In the past few months, a large section has started to die. The damage appears to be spreading. What would you advise us to do?

Answer

A sudden dieback in part of an old Griselinia littoralis hedge like this is quite likely to have been caused by phytophthora or a similar root-rot problem, particularly after the exceptionally long and wet winter we have had. 

Griselinia dislikes sitting in cold, saturated soil for prolonged periods, and older hedges can suddenly collapse once roots begin to fail.

I would remove the dead section completely, including as much of the root system as possible, and dispose of the material rather than composting it. 

Before replanting, improve the soil first by incorporating organic matter and improving drainage. 

A biochar-based plant food can help support soil structure and root recovery in the surrounding hedge. 

I would be cautious about immediately replanting with griselinia in exactly the same spot unless drainage has clearly improved. 

In wetter sites, a more tolerant hedge species may prove more reliable long-term.

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