How to Drain Soggy Soil

This soggy low site is best suited for a drain, a marsh or a pond, not a bench.

Perpetually wet soils can be remedied if you know what the problem is. Clay soils retain moisture and drain very slowly. Compacted soils are also unable to drain because that have been squished by heavy loads, parking, and frequent foot traffic. I hope the following information will help you navigate through the quagmire of waterlogged soils. 
Avoid Sand: It is a misconception that a layer of sand improves drainage but the opposite is true. Sand layers must become totally saturated before they drain to the layer below. It’s much better to mix the sand into the soil rather than lay it on top. Do not add sand to clay soils as it results in concrete.
Add Organic Matter: A much better alternative to sand is organic matter. When it’s mixed into clay soils it build soil and adds nutrients, which sand does not. Mix in fir or hemlock mulch, or use leaf mould to break up the clay and to act as a sponge to soak up the water. Mix it in well and then add a 3 inch layer of an organic mulch over top of the soil. The mulch protects the soil and reduces erosion.
Add Lime: Wet soils don’t retain calcium so they benefit from the addition of lime. Avoid fast activing lime as it’s known to burn soil and plants. Use Dolopril, a coated lime product that is slow release and easier to apply. Before adding any type of lime, get a soil pH done.
Low Areas: Sunken spots collect water, but should drain in a day at most. Filling in the depression with soil is a good way to prevent puddling. For serious low spots that don’t drain convert the area to a pond, bog garden or a rain garden.

Drain the Soil: Another option, is to install a trench (French drain) to move the water away. It is simple but very effective, permanent solution. This low tech method removes water from an area by using a trench and gravity. Look below for construction tips. 

An open trench is another way to deal with excess water.

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Plants that don't mind wet feet

Rodgersia pinnata.

Plant! If you want to go with the flow, so to speak, add plants that don’t mind wet feet. They will also help dry things out: goat’s beard (Aruncus dioicus), Astilbe, water avens (Geum rivale), Gunnera, Japanese iris (Iris ensata), Siberian iris (Iris sibirica), Ligularia, Rodgersia, redtwig dogwood (Cornus sericea), river birch (Betula nigra), swamp maple (Acer rubrum), Persian ironwood (Carpinus persica) and willow (Salix).

Gunnera manacata.

Cornus sericea, red twig dogwood.

Iris siberica, Siberian iris.

Astilbe chinensis 'Pumila'.

Aruncus dioicus, goatsbeard.

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French/Trench Drains

Saturated soils is a common issue in the Lower Mainland of British Columbia at this time of year.

Drain excess water by guiding into a trench by using gravity. This trench is designed to simulate a little brook and will be surrounded by plants.

Roll back the existing lawn to dig out a trench. Placing the soil on a tarp makes it easy to dig out the trench and replace the soil when done. No more lifting the soil into a wheelbarrow and dumping it when full.

Soggy soil, saturated beds and floating lawns are a result of poor drainage. A French drain is a simple, low tech method to removing water from an area by the use of a trench and gravity.
You will need:

• drain pipe
• scissors or knife
• washed gravel/drain rock
• landscape fabric or geotextile fabric
• shovel
• wheelbarrow
• tarp​

1. Look before you dig! Before digging, call BC One Call 1-800-474-6886 or go to their website to find out where any underground utilities are. If not from BC, call your local municipality for more information. In the USA, call 811 for their Call Before You Dig hotline.
2. Locate the low spots of the garden (where the water is pooling) as this is where you will be digging the trench.
3. Figure out where the trench is going to go and where it is going to take the excess water. Ideally, choose an area that’s 1 meter from a wall or fence, posts, shrubs and trees.
4. It is illegal to reroute the water to your neighbour’s yard. Ideally, it should drain into an area that is unused and preferably has good draining soil. Be creative and divert the trench to a depression, preferably with poor drainage, to create a bog or rain garden.
5. To mark where the trench should go, use a landscape (striping) spray paint. (It sprays when it is help upside down.)
6. Gravity – Use gravity to move the water in the trench by sloping the trench as you dig. Check it afterwards to make sure that it does actually slope sufficiently. Ideally, it should slope 6 inches for every 50 feet.
7. Use a shovel to dig a trench approximately 6 inches wide and 18 to 24 inches deep. It should be a relatively smooth trench with no dips and dives so the drainage pipe sits evenly.
8. If shovelling is too difficult, rent a trench digger. Take note as they are tough to operate and take muscle especially on rocky, compacted and/or clay soils.
9. As you dig the trench, stop and check to make sure it is sloping properly and going in the right direction.
10. Once the trench is dug, line it with landscape fabric or geotextile fabric.
11. Keep at least a foot of excess fabric on either side of the trench as it will be folded over and must overlap.
12. Add a level layer of 2 to 3 inches of gravel along the bottom of the trench.
13. Place the drainage pipe (a perforated pipe) on top of the gravel. If the drainage pipe has holes only on one side, lay the pipe so the holes are facing down.
14. Cover the pipe with gravel so there is 5 inches between the top of the gravel and soil surface.
15. Level the gravel, then fold the fabric over the gravel. It must overlap to prevent soil from infiltrating the pipe, which would reduce water flow.
16. Cover the fabric-covered trench with the soil you initially dug up to make the trench.
17. Firm the soil, add a starter fertilizer (last number highest) then lay new sod, sow grass seed or relay any sod you removed to make the trench, then water or build an open French drain.

A diagram of a French drain.

Landscape fabric is used to reduce silt build-up, which would plug the holes in the pipe.

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An Open French Drain

Although this 'stream' looks natural, it's actually man made.

​An Open French Drain – a stream bed:
If you would rather not grass the area, place at least 6 inches of beach pebbles or other large round rocks to imitate a river bed. Grow plants along the edges of the trench along the entire length of the trench or create individual beds or garden pockets.

A diagram showing the basics of an open French drain.