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Flooding & waterlogging

Perils of water: prevention and cures

Water iris and Californian poppy
Create a pond in a low-lying area

Whether your garden’s been completely flooded or it’s waterlogged, action needs to be taken to safeguard your plants – and your health.

With climate change models predicting a greater chance of wetter winters and flooding, even those gardeners whose land has never been under water may have to rethink aspects of planting and design.

Plan now for the future and don’t be caught short – water will always find a way.

10 tips to save a flooded garden

Berberis atropurpurea (purple barberry) and Acanthus mollis (bear's breeches)
Berberis atropurpurea (purple barberry) and Acanthus mollis (bear’s breeches) will tolerate mild salinity so have a greater chance of recovering from coastal flooding

1. As the water falls, draw a sketch of low-lying areas to help with replanning.

2. If the garden’s been flooded by seawater, there’s very 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.

3. Flood water is usually contaminated with sewage, but it’s not good practice to disinfect borders/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 wet, cold winter conditions. Don’t eat any fruit or veg that has been in contact with flood water.

4. If your garden floods regularly, consider building raised brick beds.

5. Paths and drives can be cleaned and disinfected to kill bacteria and reduce slipping hazards – keep off the area for up to three hours.

6. Don’t dig, rake or hose down the garden. This will spread the contamination further, where lack of sunlight and damp conditions will encourage the bacteria to multiply.

Rodgersia can tolerate damp soils

7. Plants dying from waterlogging have the following symptoms: yellowing leaves that drop off; wilting; roots are black, soft and smell of rotten eggs; growth is stunted or shoots die back. Remove detritus at once.

8. Stay off wet ground to reduce soil compaction: tell-tale signs are when water fails to drain away and puddles appear on the soil’s surface.

9. If plants have been under water for less than a week, there’s a chance they can be saved. Prune ornamentals right back, so they have less green growth to support.

10. Sow green manure to help dry out the ground and restore nutrients. Create a natural pond on a low-lying patch of ground.

10 tips to aid your garden’s recovery

Onion Rumba sets
Start off crops, like these onion sets in modules, to give the soil time to dry out

1. Vegetable gardeners shouldn’t sow until the soil is dry. Start off crops in modules.

2. Potato blight can be common. If in season, dig tubers up and store in a cool, dry place.

3. Waterlogging and compaction can create ideal conditions for Phytophthora (root rot) and other fungal attacks. Box is prone to box blight.

4. Remove any dead, diseased or dying shoots as soon as you see them.

5. When the soil has started to dry out, dig it over to help create an open structure. Work from boards to avoid compaction.

6. 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.

Rheum palmatun (ornamental rhubarb)
Rheum palmatun (ornamental rhubarb)

7. In clay soil, use plenty of organic matter and horticultural grit before planting to improve soil structure and drainage. Nutrients will have been washed away in free-draining soil, so add compost to bulk up the soil.

8. Build a drainage system or soakaway. Dig ditches filled with gravel, or talk to a builder about a pipe drainage system.

9. Rethink your planting and replace losses with 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.

10. If things are really soggy, 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.

10 tips to improve drainage

Fruit trees are very vulnerable to root rot in winter

1. Aerate the soil and plant trees and shrubs on a raised mound.

2. Add lots of compost to increase drainage and water-holding capacity.

3. Shrubs and fruit trees are vulnerable in winter, as they can’t put on new roots.

4. Make sure watercourses are left open.

5. When planning a patio, make it fall away from the house.

6. Create beds and borders close to the house to improve drainage.

7. Plant green manure.

8. Get rid of concrete drives and paths and use gravel instead.

9. Don’t walk or drive over the sodden soil.

10. Spike lawns with a motorised spiker and add lime-free sand.