He explains four golden rules on shade, early watering, gentle pruning and tackling hydrophobic compost, tailored to typical British gardens and balconies. In a UK heatwave, pots, hydrangeas and herbs can wilt in hours. They cover when to move pots, how to water, what not to prune and how to revive dried-out compost. One viewer asked, "How often would you suggest watering hydrangeas during heatwave? ", he replied, "I only water my hydrangeas once a day during a heatwave and they’re coping well.