There
are many trees which will grow successfully in soils which
are permanently moist, but few will survive long spells of
flooding or waterlogged conditions.
Air and water need to be available for plant roots. Saturated soils will have insufficient oxygen for healthy root function and may lead to root decay. A high water table will encourage roots to be produced near the soil surface, making them more vulnerable to drought in dry weather.
Preparation
Before planting trees in wet conditions, drainage may need to be improved. On soils prone to wet conditions in winter and drought in summer such as heavy clays, improve the soil by incorporating bulky organic matter or inorganic material such as coarse grit or pea shingle. This should be done over as large an area as possible - around one square metre/yard. If severe waterlogging or flooding is a problem artificial drainage will be necessary.
Planting
Improve drainage at the base of the planting hole by forking through any compacted soil. Fork through the sides of the planting hole or break down the sides into the planting hole when backfilling. This avoids creating a planting 'bucket' or sump which fills with water. On heavy soils prone to winter wet, protect the finer surface feeding roots by planting trees on a slightly raised mound to improve drainage around the root system.
Trees suited to wet soils
Alnus (alders), Salix
(willows), Taxodium distichum (swamp
cypress), Metasequoia glyptostroboides
(dawn redwood), Populus (poplars) and
Liquidambar styraciflua (sweet gum).