The development of brown leaves on a prized plant can be a worrying discovery, however, it doesn't neccessarily mean you will lose the plant. Often brown leaves are caused by environmental factors, which can be remedied by paying close attention to watering, drainage and shelter.
Why do leaves turn brown?
Plants can be harmed by many problems including pests, diseases and environmental factors, but they can only respond in a limited number of ways – developing brown leaves is the most common. As a result, figuring out what has caused leaf browning is an essential first step in protecting your plants.
Leaves can turn brown in three ways:
- Leaves can go partially brown – on the edges and tips; within the leaf; and, often, along the central vein.
- Browning can occur over whole leaves; on the top or the outside of the plant’s foliage; and within the plant’s canopy.
- Whole shoots or plants can go brown. This often suggests that the roots, stems and trunk (one or more) are the location where damage has occurred.
These are causes for browning across part of the leaf, and the controls.
Brown leaf tips or margins
Brown tips or margins often indicate drought in spring or summer. Young growth is particularly susceptible. It may also indicate establishment failure. This is particularly common where dry weather follows spring planting, prior to new roots developing into the surrounding soil.
The damage is often worse where exposure to wind dries out leaves. The damage is usually worse on the windward side of the plant. In coastal areas, salt-laden winds can also be especially harmful, but this is due to the effect of the salt as well as drying.
- Keep young plants well watered while they establish. This can take from three months to three years, depending on the plant, site and conditions
- Provide shelter from the wind by using a length of shelter fabric (available at garden centres); planting a hedge or shrubs to give protection
- Grow plants that are suited to coastal positions
Blackening within leaves
The blackening of leaves, usually starting along the vein, is due to water-logging. This is common after wet winters on heavy soils and is frequently seen on Aucuba (laurel) as a problem known as aucuba blackening. The roots, when examined, are a bluish-black and fall apart when teased apart. On larger roots the outer sheath may pull away easily, leaving the inner core. There is often a sour smell to both the soil and roots.
Symptoms of certain fungal diseases cause similar damage, such as sudden oak death, Phytophthora ramorum.
- Where waterlogging is a permanent problem, consider installing a drainage system
- Grow plants that thrive in wet soils
- Use raised beds to lift the roots clear of the winter watertable
- See our advice on Phytophthora ramorum for further information where this problem is suspected
These are causes for browning across the entire leaf, and the controls.
Brown, desiccated lower leaves
Brown desiccated lower leaves are common on climbers and this is due to dryness at the roots.
- Regular watering is particularly important for newly-planted stock but, in prolonged dry spells, even established plants may require additional watering
Whole, brown single leaves
Some leaves go brown from natural causes – evergreen leaves, for example, are long-lived, but are replaced every few years. This often occurs in summer and can be alarming. However, natural replacement is usually confined to lower and older leaves, and those within the foliage or canopy.
Whole brown leaves can also be seen after infection with diseases such as powdery mildew.
- If the powdery stage is missed, it is not always obvious that the original cause was disease. Remove affected leaves and a keep close watch for future infections
Shoot and plant browning
These are causes for the browning of whole shoots or plants, and the controls.
Entire shoots go brown
Browning of shoots suggests that something is preventing moisture reaching the affected leaves. Tracing the shoot back to the trunk can sometimes reveal cankers or other damage.
Progressive wilting and browning of shoots can be caused by fireblight or verticillium wilt disease.
- Cankers or other stem and trunk damage should be pruned out, otherwise, the affected shoots will have to be removed
Whole plants go brown
When whole plants go brown, the cause is usually in the roots or trunk. This is frequently due to poor planting and aftercare; lawnmower or strimmer damage; bark damage from the activities of rabbits and other mammals; waterlogging; or root disease, most commonly honey fungus or Phytophthora root rot. Root diseases can often be detected by examining the collar (where the trunk goes into the ground), beneath the bark.
- Ensure that plants are carefully planted and that they are looked after while they establish
- Be careful not to damage plants with mowers or strimmers
- Use rabbit collars or make a pen of chicken wire around the plant to discourage rabbit damage
- Grow in raised beds, mounds or use plants that thrive in waterlogged conditions