Be water wise this spring
6 May 2011
Guy Barter, head of RHS Advisory, gives his advice on coping with the dry weather.
Although there has been rain at last for many regions, dry soils will need about 70-80mm of rain to get soil levels back to normal. Dry springs are fairly frequent in Britain, but warm dry springs are more unusual. This year March and April rainfall has been very low. At Wisley we have recorded just 12mm for March and 1.5mm for April, when we would have expected on average 95mm for this period.
Winter rain is stored in the soil, and for plants such as trees, shrubs and climbers with large,ranging roots there is still plenty of water in the soil. However plants that have only been planted within the last two years will be vulnerable and will need watering until their root system has grown. It is hard to tell if the water has gone deep enough without using a trowel to check the soil.
Lawn care
Lawns do not usually have deep roots and are the first garden feature to show signs of drought stress. This does not matter too much as the grass can go brown but will quickly recover when rains return. Newly sown grass seed or freshly laid turf is vulnerable and will need watering. It is best to avoid sowing seed and laying turf in summer. Keeping your mowing height a bit higher will help as well.
Young plants
Seedlings and young vegetable or flower plants must be kept moist until their roots spread deep enough to access winter rain held deeper in the soil. Once plants start flowering root growth declines and they need watering. It is worth feeding as adequate fertility helps plants grown new roots to seek out moisture. Watering young vegetable plants is a priority.
Alternative water sources
Your water butts are probably low or empty by now. We suggest waiting until they are one-third empty then filling with tap water until they are two-thirds full (leave one-third to capture any storms or showers). The mildly acid rain water will counter the alkaline water found in many regions and still be good for ericaceous plants such as camellias. Gardeners are often worried about using softened water. This is safe to use, but can be expensive.
Waste water from the kitchen is highly suitable for watering gardens, grey water from the bathroom is usually satisfactory, but perhaps best not used on edible crops. Other waste water form the house is probably best not used in the garden.
In the future. . .
It is worth making a note of especially dry spots for later treatment. Boost soil water storage capacity by adding organic matter such as manure to the soil or laying it on top as mulch. Heavy manuring can add nearly a month’s worth of water storage capacity to the soil. Loam-based potting compost doesn't dry out as quickly as peat-free composts. If using peat-free, water-retaining gels might have some benefit.