WET SOIL TOLERANT PLANTS

WHAT TO PLANT IN WET PLACES

 

Too much water in part of the garden is a problem that affects many gardeners. The problem can be a constant one where it occurs all year round or it may be seasonal. It might be that the septic tank over-flow or the storm water drains into one corner of the yard resulting in at best moist soil and at worst a complete bog. It may be just a low spot that collects all the water from the surrounding area. Whatever the reason, there are ways of turning a boggy or wet area to your advantage.

Some plants thrive in wet areas, and with the right plants you can still achieve an interesting and attractive garden. There are even quite a few bog and moisture loving plants that provide "vegetables" or fruit suitable for the permaculture garden.

What Can Cause Wet Areas in Your Garden?

·         Septic runoff can be a problem, particularly in areas with poorly draining soils. Often all you get is an area where the grass or plants always seem to grow more lushly as a result of a plentiful supply of moisture (and nutrients). At times however, you may get a quite boggy patch or line along the septic runoff where little seems to grow. These areas can also be quite foul smelling at times. 

·         Waste water from your house that is drained into your garden.

·         Rising water table (eg. particularly from over irrigation in rural areas) or naturally occurring springs.

·      Water from surrounding properties may drain into your garden. This could be naturally occurring or may result from your neighbours diverting water, either intentionally or unintentionally, from their property into yours.

·         Low areas or depressions provide a site for water to collect. The water could be from rain water, garden irrigation, etc.

Problems with Wet Areas

·         It is often difficult to get plants to grow. You must choose the right plants.

·         Mosquitos and other annoying insects are encouraged by stagnant and boggy areas.

·         The presence of stagnant water can be a health hazard. It can also be very smelly.

·         Access is restricted (eg. you can sink into muddy areas).

·         Visually the area may look quite ugly. It may also be quite messy for kids and animals (fence off or plant so densely that access is restricted).

·         Pollution accumulates in wet boggy areas (ie. salts and contaminants caused by run-off). Chose only plants that can tolerate this type of  situation.

Overcoming Problems

Wet areas can be overcome in the following ways:

·    Prevent or reduce the amount of water reaching the garden. For example septic systems can be connected to the sewerage, blocked drains can be repaired, stormwater diverted elsewhere, etc.

·       Fence off, or plant trees and shrubs to screen the area off. This can prevent access to the wet area as well as blocking it off visually. It doesn't however, fix the problem.

·         By improving drainage.

Drainage should be directed to spread and dissipate rather then be captured in a concentrated area.

·         When directing drainage always spread and dissipate - do not concentrate the source.

·         Capture rainfall into planting beds or small holding areas such as constructed creek beds, which can act as small scale infiltration device and can be more cost effective than traditional storm-water designs.


Examples include:

·         Shallow, grassy swales;

·         Steeper swales, lined with ground-cover, grasses, or shrubs and trees that tolerate wet conditions

·         Constructed creek beds with stones of a size to resist excessive current force. A permit may be required.

·         For intense rainfall areas where you need to slow down water which may not be immediately absorbed, incorporate bio-swales, sumps, and impound basins into design of the site. These areas will also provide habitat for birds and animals.

·         Avoid the use of hard surfaced culverts which divert water as these can cause problems to neighbours or further down-stream.

·         Improving soil drainage capacity.

How to Improve Drainage

1. Heavy clay soils:

·         Dig in lots of organic material (eg. mulch or wood-shavings). As this decomposes it improves soil structure and nutrition, helping drainage as well as increasing the soil's capacity to absorb water.

·         Add gypsum or clay breaker. These products open up hard soils allowing better drainage.

·         Install drainage pipes to take the water away.

2. Low spots:

·         Dig organic matter into the soil to help absorb excess water and improve soil structure.

·         Create a sump pit at the lowest point (see section on creating a sump)

    

3. Raise levels or fill depressions:

·         Get an earthmoving machine in (or do it by hand if it’s not a big job) and change the levels of your property so water drains away instead of collecting in any one part.

·         Build a raised garden bed on the surface of the ground.

4. Plant with water loving plants:

·         If the area is always wet (eg. from septic overflow), use plants which like a continuously wet soil, and do not mind being waterlogged at times (eg. Iris, papyrus etc). Spread a 4‑5cm layer of coarse sand or pebbles over the surface to restrict the growth of algae or any other putrid smells.

·         If the area sometimes dries out - create a bog garden by digging out the area, lay a double thickness of black plastic, fill with a good quality, highly organic compost then plant with bog plants. Or use plants which tolerate or even like being waterlogged but will tolerate some drier periods.

5. Build a pond and drain the surface water into the pond.

If You Have Nowhere to Drain to

Often the home gardener will find that they have nowhere to drain excess water to. One way of overcoming this problem is to dig a sump. This has proved very effective for disposing of septic runoff.

The sump can be located at the end of the septic runoff or elsewhere in the garden away from your house. Try to avoid placing it near other pipes, drains, etc. The technique for creating a sump is as follows:

·         Excavate a hole approximately 1 x 1 x 1.5 metre large. The soil removed can be used elsewhere or discarded.

·         Fill the hole to within 20‑30 cm of the surface with coarse material such as builder’s rubble, rocks, gravel, etc.

·         Lay your drains or septic outlet so that they terminate (discharge) level with the top edge of the gravel.


·         Add a layer of 10‑15 cm of sand then fill the remaining part of the hole up to ground level with good quality sandy loam or loam soil.

·         Plant lawn or other plants over the excavated area.

 

Other Problems with Wet Gardens

·         What if there are times when it goes dry? Choose plants which will tolerate this - or else you need to water, mulching also helps.

·         Direct sunlight may dry the bog out. Sufficient light is required, however, for plants to grow. Partial overhead shade may be required; mulching will also help reduce surface drying out.

Algae and moss will thrive and become a problem on wet soil if light is allowed to reach the soil (algae need light to grow). A layer of coarse sand or gravel spread over the surface will help control algae, as will spraying it with an iron sulphate solution. Planting long grasses/reeds, etc. shades the soil and reduces the chances of algae and moss growing. Barley straw (not hay) placed in the bottom of the pond helps to eradicate algae within about 6-8 weeks.  

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PLANTS SUITED TO BOG GARDENS

The following are just some examples:

Plant that Grow Well In Wet, Shaded Places

Kalmia latifolia

Cornus (Dogwood)

Dicksonia antarctica  (Tree Fern)

Blechnum sp.

Nephrolepis (Fishbone Fern)

Vaccinium sp. (Blueberry)

Iris versicolor

Lilium canadense

Mentha (Mints)

Myosotis (Forget‑Me‑Not)

Oxalis montana (Wood Sorrel)

Viola cucullata (marsh blue violet)

Viola rotundifolia (round-leaved violet)

Plants that Tolerate Periods of Moist to Flooded Soil- but not drought tolerant

Iris

Papyrus

Tolerate Wet and Polluted Areas (where sullage/household waste etc accumulates)

Carex fascicularis

Crassula helmsii

Melaleuca ericifolia

Acacia melanoxylon

Eucalyptus ovata

Callistemon citrinus

Callistemon viminalis

Very Tolerant of Wet soils

(Will withstand soil being submerged in water for lengthy periods)

Abies balsamea

Acer negundo, rubrum, saccharinum

Carya aquatica, illinoensis, ovata

Cretaegus mollis

Diospyros virginiana (persimmon)

Cornus sericea

Fraxinus pennsylvanica(green ash)

Eucalyptus camaldulensis

Gleditsia aquatica, triacanthos

Hamamelis virginiana

Platanus acerifolia, occidentalis

Liquidambar styraciflua

Quercus bicolor, macrocarpa, palustris

Populus delatoides

Washingtonia robusta (Mexican fan palm)

Salix alba, nigra

Virburnum cassinoides


Ferns Particularly Tolerant to Wet Soils

Bechnum siscolor, indicum, minus, wattsii

Cyathea australis, smithii

Cyclosorus interuptus

Dennstaedtia davallioides

Dicksonia antarctica

Diplazium dietrichianum, esculentum

Nephrolepis sp.

Osmunda regalis

Pteris comans, umbrosa

Thelypteris confluens

Todea barbara

Perennials for Bog Gardens

·         Gunnera manicata- ‘giant rhubarb’ large umbrella-like leaves and prickly stems. In cold areas (prone to frost and water freezing) cover the crown with the dead leaves when it dies down in winter to protect the crown.

·         Primula pulverulentaand candelabra primula flowers appear in early summer arranged in tiers up the stems.  These plants self-seed readily in boggy areas - building up beautiful large displays.

·         Darmera peltata‘Nana’ - pink flowers appear before the foliage. Large saucer-shaped leaves appear after the flowers have faded. Beautiful, fiery foliage colours in autumn.

·         Lobelia ‘Queen Victoriais a beautiful moisture-loving plant with upright stems of deep-red leaves topped with crimson flowers. Insulate the crowns with bracken or dead leaves in winter.

·         Lythrum salicaria‘Blush’ - a cultivated form of wild purple loosestrife; smaller than the wild plant; produces pale pink flowers in summer.

·         Astilbe chinensis - fluffy pink flowers over attractive clumps of low-growing foliage to 20cm

·         Iris siberica - Medium-height tough perennial with finer foliage than its larger-flowered cousins. Flowers come in many shades from white to dark blue.

·         Ligularia dentata - this clump-forming plant has both ornamental foliage and flowers. Foliage wilts in hot summers if plants are exposed to direct sun light. Suitable for shaded areas along ponds, bogs or streams. Monitor plant for snails and slugs.

·         Persicaria bistorta - A semi-evergreen and hardy, reliable perennial, excels in moist to boggy soil near water. Dense clumps of ground hugging foliage produce masses of soft pink poker heads held above the foliage throughout the summer. Native to parts of the <st1:country-region>UK</st1:country-region>.

Extra Hardy

Bog plants that tolerate full sun, wind and periods of dry to periods of flooding eg. dry summers after wet winters.

Acacia floribunda, retinoides

Brachysema lanceolatum

Eucalyptus rubida, viminalis

Grevillea confertifolia, juniperina, laurifolia

Trees for Wet Places

While there are a large range of trees suitable for wet places, it is important to note that some of these trees are too large for the average suburban backyard, or have very invasive roots that can cause problems such as blocked drains, raised paving, cracked foundations, etc. Good examples are poplar and willow species, which have been used extensively to stabilise stream banks - in the long term they may choke the stream, and require removal.

Trees That Tolerate Wet Soils

Acer freemanii (Freeman maple); mature height is 16-20m. Varieties include 'Armstrong', 'Autumn Blaze', and 'Celebration'.

Amelanchier spp. (serviceberries); mature height varies from 3-8m

Betula nigra (river birch) mature height  15-20m 

Carpinus caroliniana; (American hornbeam); mature height 6-10m

Fraxinus pennsylvanica (green ash);16-20m

Quercus bicolor (swamp white oak); mature height 20m

Quercus palustris (pin oak); mature height 20-22m

Taxodium distichum (bald cypress); a deciduous conifer to 16m



Trees for Damp Places

Damp, but not constantly wet/waterlogged, or that occasionally flood:

Acacia dealbata, melanoxylon

Alnussp. (alders)

Angophora floribunda

Eucalyptus botryoides, E. leocoxlon, E. ovata, E. saligna(Sydneyblue gum), E. spathulata, E. viminalis (manna gum).

Ficus rubignosa(invasive roots – needs plenty of room)

Liquidamber styraciflua

Poplus nigra ‘Italica’, P. serotina “Aurea’

Quercus palustris, Q. Velutina

Tristaniopsis laurina

Trees That Cope With Extended Wet Conditions

Casaurina cunninghamiana, C. glauca

Callistemon viminalis(large shrub to small tree), C. salignus.

Eucalyptus camaldulensis(River Red Gum), E. crenulata, E. robusta (Swamp Gum),

Melaleuca ericifolia, M. leucadendron, M. squarrosa, M. stypheloides

Taxodium distichus

Shrubs for Damp Conditions

Damp, but not constantly wet/waterlogged:

Aucuba japonica

Kalmia angustifolia

Callistemon linearifolius

Prostanthera lasianthos

Doryanthes excelsa(Gymea Lily)

Viburnum opulus‘Sterile’

Hedichycium sp.(Ornamental Gingers)

Weigela florida(syn W. Rosea)

Heliconia (most species and cultivars)

Shrubs for Wet Places

Aronia arbutifolia(red chokeberry)

Banksia robur (swamp banksia)

Bauera rubiodes

Callistemon citrinus, C. macro-punctatus, C. pachyphyllus, C. paludosus, C. pinifolius, C. rigidus, C. subulatus.

Cassinia vauvilliersii

Cephalanthus occidentalis (buttonbush)

Cornus sericea (red osier dogwood)

Hypericum(various)

Ilex verticillata  (winterberry holly)

Leptospermum scoporium

Melaleuca thymifolia

Olearia floribunda, O. glandulosa

Salix purpurea(purple osier willow)

Sambucus canadensis(American elder), Sambucus nigra




Marginal Plants

These are plants commonly found growing around the edges of wet areas such as ponds or boggy places. They may have all or part of their roots constantly wet, or may be exposed to fluctuating wet and dry conditions.

Acorus gramineus

Ghania radula, G. melanocarpa, G. sieberiana(saw sedges)

Alpinia caerulea(native ginger)

Isolepis sp.

Anigozanthos flavidus(kangaroo paw)

Iris kaempferi, I.pseudoacrorus

Baumea juncea

Juncus species

Calocasia esculenta (taro)

Orontium aquaticum

Caltha palustris

Phragmites australis

Carex species

Phormium tenax

Chorizandra enodis (black bristle rush)

Pontederia cordata

Cyperus lucidus, C. papyrus, C. rutilans

Restio complanatus, R. teraphyllus.

Dianella tasmanica

Sagittaria sagittifolia

Eleocharis dulcis

Thalia dealbata

Equisetum hiemale

Triglochin species (eg. Triglochin procera)

Typha domingensis(bullrush, cumbungi)

Mat Forming/Creeping Plants That Grow at Water’s Edge

Achillea (yarrow)

Marsilea sp.

Ajuga reptans

Mentha sp. (mints)

Cotula coronopifolia

Montia australasica

Crassula helmsii

Myriophyllum sp.

Isotoma fluviatalis

Pratia species

Liaeopsis brasiliensis

Ranunculus species

Viola hederacea.


 
If you want to know more about selecting plants for wet soil, have a look at our Plant Selection and Establishment course or Water Gardening course.
 
 
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