The perils of water: preventing floods and curing waterlogging
Whether your garden’s been a victim of flooding or waterlogging, action needs to be taken to safeguard your plants – and your health. Climate change models predict a greater chance of wetter winters, unpredictable rainfall and flooding. Even those gardeners whose land has never been underwater may have to rethink aspects of planting and design. There’s more on the National Flood Map.
Plan now for the future and don’t be caught short – water will always find a way. Do read up about Storm Protection. They often occur hand in hand. Read more about rain gardening to stop flooding.
Tips to save a flooded garden
As the water falls, sketch low-lying areas to help with replanning. If the garden’s been flooded by seawater, there’s little you can do to get rid of the salt, except lift plants, wash off the soil and replant in containers. The saline build-up in the soil will be washed away in time. Flood water is usually contaminated with sewage. Don’t disinfect borders or lawns, as it can kill plants. The sun’s UV radiation will kill this type of bacteria. It should return to background levels in approximately nine days in the summer and 25 days in a wet, cold winter. Don’t eat fruit or veg that has been in contact with flood water.
If your garden floods regularly, consider building raised brick beds. Paths and drives can be cleaned and disinfected to kill bacteria and reduce slipping hazards. Keep off the area for up to three hours. Don’t dig, rake or hose down the garden. This will spread the contamination further. Lack of sunlight and damp conditions will encourage the bacteria to multiply.
Plants dying from waterlogging have typical symptoms. Yellowing leaves that drop off, wilting, black roots that smell of rotten eggs, stunted growth and dying shoots. Remove detritus at once. Stay off the wet ground to reduce soil compaction. Tell-tale signs are when water fails to drain away, and puddles appear on the soil’s surface.
If plants have been underwater for less than a week, try to save them. Prune ornamentals right back, so they have less growth to support. Sow green manure to restore nutrients. Create a natural pond on a low-lying patch of ground.
How to aid your garden’s recovery
- Vegetable gardeners shouldn’t sow until the soil is dry. Start crops in modules.
- Potato blight can be common. If in season, dig tubers up and store them in a cool, dry place.
- Waterlogging and compaction can create ideal conditions for Phytophthora (root rot) and other fungal attacks. Box is prone to box blight. Remove any dead, diseased or dying shoots as soon as you see them.
- When the soil has started to dry out, dig it over to create an open structure. Work from boards to avoid compaction.
- Fruit trees and bushes may suffer from root rots and be liable to wilting in dry spells. Mulch, water and feed during the growing season.
- In clay soil, use plenty of organic matter and horticultural grit before planting to improve soil structure and drainage. Nutrients wash away in free-draining soil, so add compost to bulk up the soil.
- Build a drainage system or soakaway. Dig ditches filled with gravel, or talk to a builder about a pipe drainage system.
- Rethink your planting. Use water-tolerant species, such as Cornus alba, C. stolonifera, Hydrangea macrophylla, H. paniculata, Kerria japonica, Leycesteria formosa, Weigela, Salix, Betula, Sambucus, Liquidambar, ash and Amelanchier.
- Make a bog garden. Suitable plants include Iris ensata, I. laevigata, I. pseudacorus, I. sibirica, primulas, Actaea, Astilbe, Carex, Gunnera, hostas, Rheum palmatum (ornamental rhubarb) and Rodgersia.
Tips to improve drainage
- Aerate the soil and plant trees and shrubs on a raised mound.
- Add lots of compost to increase drainage and water-holding capacity.
- Shrubs and fruit trees are vulnerable in winter, as they can’t put on new roots.
- Leave watercourses open.
- When planning a patio, make it fall away from the house.
- Create beds and borders close to the house to improve drainage.
- Plant green manure.
- Get rid of concrete drives and paths and use gravel instead.
- Don’t walk or drive over the sodden soil.
- Spike lawns with a motorised spiker and add lime-free sand.
For more on floods, unpredictable rainfall and their impact on the climate, visit www.metoffice.gov.uk.
