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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.
Brown leaves. Image RHS/John Trenholm
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:
These are causes for browning across part of the leaf, and the controls.
CauseBrown 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.
CauseThe 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.
Similar symptoms can be caused by certain foliar diseases, such as Phytophthora ramorum.
These are causes for browning across the entire leaf, and the controls.
CauseBrown desiccated lower leaves are common on climbers and this is due to dryness at the roots.
CauseSome 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.
These are causes for the browning of whole shoots or plants, and the controls.
CauseBrowning 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.
CauseWhen 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.
Various pests and diseases can also cause browning of leaves; and these possibilities cannot be ruled out.
Common pests include bay sucker, deer, rabbits and grey quirrels.
Common diseases include bacterial canker, blossom wilt, fireblight, honey fungus, horse chestnut leaf blotch, Phytophthora root rot and powdery mildews.
Leaf damage in woody plantsNon-flowering woody plantsTrees and shrubs: establishment problemsTrees and shrubs: plantingWaterlogging and floodingWeather damageWhy has my tree or shrub died?
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