Tony Dickerson answers your questions
QAre the brown patches on our viburnum leaves due to drought? Alan and Julie Rogers, Frome, Somerset
AA new shrub in the ground for less than a year will certainly be more susceptible to drought. Most gardeners will water new shrubs on planting but until a good root system is established, additional watering may be needed in dry spells for up to two years afterwards.
Watering would seem simple but I suspect that the majority of gardeners get it wrong. The most common error is spraying water over plants. This does nothing apart from encouraging fungal infection. Plants have specialised structures to take up water – roots – that have evolved over 400 million years and they are found in the ground. It makes a lot of sense, therefore, to direct watering at the soil. It’s also better to water the garden before drought sets in, as it’s very difficult to rewet very dry soils, with most of the water flowing off the surface. Organic mulches will not only conserve moisture but also allow irrigation water to percolate gently into the soil. Ideally, water plants in the morning or evening to avoid evaporation. How much to apply? It’s more than you think. A regularly- watered garden in dry spells will need about 24 litres per sq metre (5 gallons per 10 sq ft) every seven to 10 days to maintain plant growth. A sandy soil in which plants are wilting might need 60 litres (12 gallons) and a clay soil 81 litres (17.5 gallons) to restore wilted plants.
This may sound the wrong way round but clay soils bind water molecules very tightly to them so can feel damp but have no available water that plant roots can extract. Of course there are many plants that are adapted to dry climates and will tolerate drought with no additional watering once their roots are established (see below).