What is it?

Soils become waterlogged when water builds up, unable to drain away. This leaves no air spaces in the saturated soil, and plant roots literally drown.

Short-lived flash floods after a downpour seldom harm most plants. It is prolonged, saturated soil that cause the most damage.

Symptoms

Symptoms of waterlogging are not easy to tell from other disorders but look for the following;

• 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, a typical sign of waterlogging that may be accompanied by a sour, rotting smell. Roots may rot away completely, with few remaining. 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
• Herbaceous plants may fail to sprout in spring, or leaves may open and then die
• Plants may be stunted, or even die
• Some plants suffer from a condition called oedema

Some of the symptoms are easily confused with water stress (too little water). But in fact, a waterlogged plant actually is water stressed. This is because the roots are drowning and can not absorb any water or nutrients to move around the plant.

Cause

Excess water causes problems for plants in a number of ways;

• Waterlogging limits oxygen supply to the roots and prevents carbon dioxide from diffusing away. Root function is reduced or stops and the roots start to die off, allowing the invasion of rots and decay organisms. This has a subsequent effect on the visible parts of the plant, as the leaves and stems are unable to obtain enough water and nutrients
• In cold, winter soils, roots respire little, so waterlogging is much less damaging than during warm seasons, when roots respire freely and demand more oxygen. Few plants can survive summer waterlogging, unless they have special roots adapted to such conditions. Willows and marginal aquatic plants such as flag irises are examples of these
• Waterlogged soils may be compacted or have a naturally dense texture lacking drainage channels. This means that the soil remains wet after rain

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