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Garden Drainage Help Needed

ODog
10 years ago

Hello everyone. This is my first post, so please be kind if it's the wrong forum, or something that has been discussed at length previously.
I have a garden on top of a timber retaining wall. It contains a row of Miscanthus grass and many dollars of dead phlox. The plants are dieing because the area stays wet. It does get a good amount of sun. I'm looking for ways to address this. The wall is 29 in tall by 35 feet long and the garden is 3 feet deep.
Digging a hole approx 2ft deep, I discovered the soil is quite dense, much like loam.
Because of the 'dead men' that run perpendicular to the wall, under the garden, I cannot add a perforated drainage pipe the length of the wall.

Do I dig everything out, add stone and sand? Then top off with 12in of garden soil? If so, how many inches deep of each? Would this have to be done for the entire footprint of the garden (my back already hurts :)) ?

Can I just add peat moss or sand to the top 12in of soil? This would be a lot easier, but not sure it will be effective.

I don't mind the effort, but if I do it, want to make sure it will work. Thanks for any advise or suggestions.

Comments (3)

  • jean001a
    10 years ago

    Consider hiring a soil engineer for an onsite visit & suggestions.

  • Kimmsr
    10 years ago

    Loam is not a soil type that would be dense mostly because it is about 45 percent Sand, 25 percent Silt, 25 percent Clay, and maybe 5 percent organic matter. So you need to determine what type of soil you do have.
    Clay soils tend to hold too much moisture because the very small soil particles do not allow the moisture to flow easily. Adding sand or stone for drainage may be too costly.
    Perhaps these simple soil tests mightbe of some help.
    1) Soil test for organic matter. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

    2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drainsâ too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

    3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

    4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell.

    5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.

  • ODog
    Original Author
    10 years ago

    Wow. Thank you!

    I'll work on this over the coming days. I'm sure I'll have follow up questions, of which I'll post, if that's OK with you.

    Thanks again.
    O