Here's an earlier thread I read with a similar question. Maybe it will help.

Here is a link that might be useful: Plants to go under a very shady deck

Not much thrives in the dark under decks, even when it grows, and scraggly looks as bad as bare.

What I did that works and looks pretty good was to make three terrace levels with landscape timbers since my under deck sloped sharply. A single border would work if the area is flat. Then on each level I put down weed barrier and a couple of inches of bluestone dust, which is pretty inexpensive. The color lightens up the dark area so it doesn't have the dungeon feel. For eye appeal on the great expanses of bluestone dust, I have placed a few interesting rocks (I've liked the black smooth stones from Smith and Hawkins best so far). Sometimes I rotate in a couple pots of impatiens when I'm feeling especially decorative, usually twice a summer.

I usually have to refresh the bluestone dust every three years or so by adding a top layer of two or three bags--about $20 worth

If the perimeter of your under deck area gets some light, just make the border back a few feet to contain the bluestone dust and plant the edges with hostas, sedges or other shade plants. The bluestone dust reflects light so it will be easier to grow the border plants.

:) corydalis lutea seems to thrive in the darkest corners- so it should fill in behind the hostas quite nicely. behind that, though, it's very possible that nothing will take but mosses, which need the least amount of light...

a nice bed of silver cushion moss would look striking under the deck :)

Sorry for the late question but, KimKa, what is bluestone dust? I've not seen it here in central Iowa. Anything that can brighten under a dark deck sounds useful. I have a dark area next to my garage in dry shade (BIG silver maple)with truly horrible clay subsoil fill dirt. Even creeping charlie struggles there! How thickly does it need to be applied? I don't like weed block fabric but would you advise putting that down first? I've tried wood chips and mulching with grass clippings -- I have lots of those. I'd like to try a different look. Thanks. mmo

Bluestone dust is a very fine grind of a type flagstone. The color is a very light kind of a steel blue. The stone dust packs down and interlocks well so it does not wash away or float easily. It is often used as a base for laying patio or path pavers and sometimes in mortar mix, as well as for paths and drives by itself. I love the color of it and it reflects light well.

I use about a 1 1/2- to 2-inch layer with weed block to ensure that I don't have to pull up an occassional struggling weed. I'm sure a thicker layer of stone would do almost as well at keeping the weeds out. I would not recommend bluestone dust as a landscape dressing to grow plants through.

Look in the yellow pages under rock or stone and call to ask about bagged bluestone dust. Some places will also carry bluestone chips, whch is a larger size stone.

What is the distance between the ground and the underside of the deck?

Barb

Thanks i used this info for a school project. I haven't been on here forr a while. Ever since we moved to MT. I used to live in WA. you need shade plants here!(those in the sun die from it!)
To view results from my experiment link below