Why experts are keeping a worried eye on Ireland’s heatwave and what all gardeners simply MUST do from now on as climate change brings on ‘early autumn’ effect

The Botanic Gardens may be bustling with visitors making the most of the sunshine, but behind the scenes some of Ireland’s most important trees are showing signs of stress and turning brown.

After enduring seven consecutive weeks of scorching temperatures – the country’s longest sustained dry spell since 1976 – parts of the Botanic Gardens in both Glasnevin in Dublin and at Kilmacurragh, Co. Wicklow are beginning to feel the effects and entering an ‘early autumn’. 

Horticultural staff are closely monitoring vulnerable species as prolonged heat and a lack of rainfall take their toll.

The Royal Botanic Gardens at Kew in London is already struggling with the same conditions and staff here admit that certain species are now under pressure and the gardens are preparing for a future where summers like this become more common.

The curator of the National Botanic Gardens, Dr Darach Lupton, told the Mail that the long dry spell has pushed certain species into early autumn behaviour. 

‘In general, things are just not as vibrant as they would be,’ he said. 

‘Water is not readily available. 

‘The trees are slowing down their growth.’

He explained that drought can bring on early colour changes, making leaves fade or shift tone weeks ahead of schedule.

‘Often if you have droughts like this, the effects of the things you would normally see in the autumn start earlier,’ he said. 

‘Leaves begin to change colour a little bit. 

‘It basically just accelerates that whole process.’

This means that while some trees may look worn out, it does not necessarily mean they are failing but it is a natural response to six weeks of heat and little rain.

The National Botanic Gardens at Kilmacurragh have recently enjoyed a major upgrade, with the development of a wildflower meadow, and extensive planting of trees and shrubs which are more vulnerable to the dry conditions. 

Dr Lupton says that although most of their mature trees are coping well, there are a few species that could begin to struggle if the heat continues. 

‘Trees by their nature are quite resilient,’ he said, ‘but if we were to identify species that might be at risk, there are things like beech trees, birch trees, alder trees and poplar.’

These trees naturally grow close to wetter ground, so they feel the pinch faster when rain disappears.

‘Some areas in the gardens have very free-draining soil, rich in gravel, so it does not retain moisture very well. 

‘You have that double impact of the species not being naturally resilient to drought and the environment not helping.’

He explained that trees from places like the Mediterranean, California, Australia and South Africa have built‑in ways to conserve water, such as smaller leaves, deeper roots or the ability to close the tiny pores on the underside of their leaves.

Although most mature trees can cope with a dry spell, Dr Lupton says the team has been keeping a close eye on anything planted in the last two years. 

Young trees have smaller root systems and feel the pressure fastest.

‘We are very conscious of conserving water,’ he said. 

‘We are just keeping them watered enough to keep them alive until the next rains come.’

Looking ahead, he says both the gardens and the public will need to adapt their planting choices as summers become hotter and drier.

‘The selection of plants will have to be in line with drier summers,’ he said. 

‘We need to be selecting trees that are going to be able to tolerate drier springs and drier summers and potentially wetter, stormier winters.’

He points out that this is not just an Irish problem. 

‘Every other botanic garden in the world is facing this issue,’ he said. 

‘We have seen a lot more visitors with the good weather. 

‘Everyone else is coming in and enjoying it. 

‘For me it is a stressful thing, but our visitors are enjoying it.’