Flooding in the home has a devastating effect on the building, its contents and the wellbeing of its owners. While nowhere near as heart-breaking, flooding and waterlogging in the garden can have a devastating effect on the plants.
Nearly all plants need a constant and regular supply of water for their roots to absorb and so ensure strong, healthy growth. But very few plants – apart from plants like willows, bog plants and those that naturally grow in water – will survive if they’re roots are growing in constantly and overly wet, flooded or waterlogged soil or compost for prolonged periods.
Roots need air to breath, and they get this air from tiny air pockets between the soil particles. During flooding, waterlogging and overwatering, these air pockets are filled with water, driving out the air. The roots literally suffocate, start to rot away and die.
As a result, the plant cannot absorb water from its growing medium and so the plant starts to wilt, showing more-or-less identical symptoms to drought and underwatering.
Waterlogging is always worse on very heavy clay soils, which haven’t been improved to help prevent waterlogging and to ensure they drain as quickly as possible. But flooding will affect all soils, including light sandy soils.
Overwatering is unlikely to happen in the garden – unless a hosepipe is left on for far too long – but is common in containers – especially those with no, few, small or blocked drainage holes. It is very common with houseplants – the commonest reason for houseplants to wither away and die – as many of us tend to overwater our houseplants – “killing them with kindness”!
New and recently plants are usually more susceptible to waterlogging and flooding than well-established ones, since they haven’t built up a fully developed root system.
Overwatering and irregular watering – cycles of drying out and flooding – can cause other, more specific problems in some plants. This includes blossom end rot in tomatoes.