RHS advice on what to water, what to leave
28 June 2010
The Royal Horticultural Society is warning gardeners that soil dryness levels have already fallen to a low often not encountered until late July/August. The recent low rainfall has led to soils having a moisture deficit of four inches, meaning that four inches of rain would be needed to restore the soil to full moisture capacity.
“It would have to be unusually rainy now to fully replenish the soil so vulnerable plants may need supplementary watering,” says Guy Barter RHS Chief Horticultural Adviser. “Most established trees, shrubs and climbers should have sufficient roots to withstand this level of dryness by using water stored in the soil from winter rain, but as summer rain is seldom sufficient for newly planted trees and shrubs I would suggest that ones planted in the last two years will need watering every 10 days even if there is some rain now.”
The RHS advises that early flowering perennials that have finished flowering can be left to die back. Late flowering perennials will need watering unless the soil is particularly heavy and moist. Raspberries, strawberries and other fruits are likely to respond to some watering. Lawns can be kept green by frequent watering but it is questionable if this is a sensible use of water, when brown lawns will quickly green up when the rain returns.
“If at all possible it would be useful to group containers, especially the very vulnerable hanging baskets, in light shade which will help reduce drying out,” says Guy.
The RHS suggests that watering the soil is best practice rather than watering plants and to do this consider making ‘ponds’ round individual plants so that the water can really soak in, ideally wetting the soil quite deeply, say to 25cm (10ins). Thorough watering like this supports plants for 14 days, but merely wetting the surface wastes water, encourages weeds and can lead to surface rooting making the plant more vulnerable.
Getting the soil right is also important. Guy explains: “Having your own compost heap will not only help reduce the amount of waste going to landfill but also will give gardeners an ideal medium to help make their soils even better for plants,” says Guy.