All hedging plants obviously need water but, with the exception of Hornbeam (hardly surprising given its love of damp conditions), most have a fair degree of drought tolerance.
The most drought tolerant include:
• Beech (Fagus sylvatica)
• Griselinia Littoralis
• Lonicera nitida
• Perovskia Blue Spire AGM (Perovskia atriplicifolia ‘Blue Spire’)
• Photinia Red Robin AGM (Photinia x fraseri ‘Red Robin’)
• Privet (Ligustrum ovalifolium)
• Purple Copper Beech (Fagus sylvatica ‘Purpurea’)
• Yew (Taxus baccata)
The following hedging plants will still tolerate drought, but to a lesser extent:
• Cherry Laurel (Prunus laurocerasus ‘Rotundifolia’)
• Common Box AGM (Buxus Sempervirens)
• Escallonia Macrantha AGM
• Euonymus fortunei ‘Emerald ‘n’ Gold’ AGM
• Euonymus fortunei ‘Emerald Gaiety’ AGM
• Leylandii (Cupressocyparis Leylandii)
Lavenders and Rosemary planted into the ground rather than in containers are well-adapted to seeking out moisture for themselves, their drought tolerance greatly enhanced by their plump foliage designed to store water
NB: Once a hedge is fully established, it should only need watering in times of drought. Before then, though, and certainly during its first year, a hedge will need additional water unless there has been unusually abundant rainfall.