Martyn Davey, Head of Horticulture and Design, Easton College
Monday, May 21, 2012
Question: Two years ago I planted a hedge of 50 cherry laurels. They are now looking rather ick with spindly growth, the leaves are pale green and some have turned yellow and brown. I have tried feeding them with dried poultry manure pellets, which has not worked. The soil has a high clay content and during dry periods goes very hard. But another four cherry laurels which I planted only five yards away from the others have grown very well. (M Newson, Roydon)
The problem seems to be that your soil is waterlogged and few garden plants will survive waterlogging or flooding. Prolonged periods of sitting in ground saturated with water causes yellow leaves, root rot and death. However, conditions can be improved.
Short-lived flash floods after a downpour seldom harm most plants. It is prolonged, saturated soil that cause the damage.
The first symptoms appear on the leaves. This includes yellowing or decay between the veins, resulting in soft areas at the base or centre of the leaf. There may be dark areas along the midrib, and areas within the leaf go brown, especially on evergreen leaves. The plant may also look like it is short of water, even wilting. A root sample will show blue-black roots, which may be accompanied by a sour, rotting smell. Damaged roots will be blackened and the bark may peel away. Shoots may die back due to a lack of moisture (the roots cannot supply water to the leaves) and bark peels off the shoots easily.
One way to help prevent this problem is to improve the soil structure and drainage through cultivation. Avoid smearing the sides of planting holes on heavy soils – or prick the sides of the hole with a fork before planting. Consider planting trees on a slight mound. If there is somewhere for water to go, drainage can be installed. Or, where appropriate, it may be worth digging out a ditch or seasonal pond at the lowest part of the garden.
Or you can select plants that will cope with the wet conditions: Photinia is a popular evergreen shrub. The best known is Photinia × fraseri ‘Red Robin’ which is often planted as a specimen shrub or as a fast-growing, dense, evergreen hedge.
Photinia grows in fertile, moist, well-drained soil in sun or partial shade.
Photinia grows in most soils, even clay as long as it has been improved by incorporating well-rotted compost or manure. Most species will tolerate either acid or alkaline conditions, but P. beauverdiana and P. villosa are not happy in a chalky soil, needing neutral to acid soil conditions.
Hornbeam (Carpinus betulus) grows wild in the south and east of England, where it may form woods and copses on its own or mixed with other species. This tree looks very similar to beech but it has a greater tolerance of damp clay soils. The bark is grey with a silvery tinge, and the leaves produce attractive yellow and orange autumn colours. The female flowers are greenish catkins up to 12cm long and the fruit is a small nut. Hornbeams have a moderately slow growth rate reaching 6m high and 4m across in 10 years, 11m x 6m in 20 years and 25m x 20 when fully grown. Don’t be put off by the ultimate size as they make a great hedge.