The separator fabric serves two purposes: stabilizing the base for the gravel mulch (which is not really important since it will be below a deck, and therefore without traffic) and it allows for clean removal of the gravel at some later date should it ever be decided it's no longer wanted, or if some type of repair must be made requiring excavation below it. It is not, over a period of time going to help with weed prevention. Lack of light below a deck and the gravel itself (a little) will help with that. Any weeds that infiltrate (there won't be many) can be pulled, chemically removed or ignored as the owner sees fit. To use something that will decompose as a separator will not help at all with the later removal of gravel if it is ever decided to get rid of it. Also, it will not help with weed prevention. What would be the point of using something that decomposes? (Unless the entire mulch is biodegradable and the "separator" is used for initial weed "smothering" purposes?)

RE: At least 12 benefits are realized when using newspaper and cardboard approach to landscape covering in addition to applying it only once each season (11) and never having to ever remove it. (12) Plus its FREE!!! (13 = bakers dozen). Prepare the dirt for planting. Mark row with a string and small stake at each end of the row so you will know where you intend for plants to grow. Make rows. Transplant or seed the garden rows. "Cover all areas" where a transplant or seed does not exist "with no less than 4 layers of newsprint up to within 1 inch of the plant or seeded rows" (do not cover seeds in rows or plants) . "Top the newsprint with 6 inches of cut lawn grass." (Most neighbors just throw grass clippings in a garbage can, which begin to deteriorate and stink waiting for garbage collection day. Ask for their discarded clippings. They will be happy to be rid of them. Good idea to provide a container or wheelbarrow for them to empty their lawn mowing bag into. Have them put grass clipping filled container on the street, a signal for you to collect. Collect the same day from their property. Clippings are easiest to work with when freshly cut.) After seedlings are up and thinning has been accomplished, you can fill in the 1 inch opening with the dry grass clippings to eliminate day light and exposure to direct air/airborne travelers-weeds. For most, the leaves and the expansion of the stem will take up most of the area and require no further attention depending on type and distance of crop. BENEFITS 1.) Keeps out the weeds, 2.) Holds in the moisture longer 3.) Allows for rain or any type of water system above or below newspaper/grass clipping barrier which gently waters crop 4.) Forms airy barrier between the ground and the plant so fruit/vegetable never sits in water/dirt and rots, 5.) Grass will turn white/tan color providing a nice background contrast for the green plantings,6.) Any weed that happens to be green and is not purposefully planted will be easy to spot and pull, 7.) Grass clippings provides a nice mud-free walkway for your shoes/feet when harvesting AND does not allow for germination of airborne or shoe-tracked seeds 8.) News-print and grass clippings are both biodegradable, deteriorating slowly throughout the growing season 9.) Rototill ALL of the garden complete with any discarded plant parts (stems, roots, leaves, fruit... discarded there in the garden through out the growing season) ALONG WITH the original newsprint and dead grass clippings, back into the ground. 10.) All will continue to decompose throughout the remainder of the year enriching your garden with the nutrients of free mulch. Bonus reward: If you want to replant in an area where you harvested an early crop, later in the same season, it will be easy to pullup those roots and the ground will be weed-free. Til or hoe to prepare soil and replant. Next season: repeat. It is recommended by professionals to rotate the place where you planted crops the previous year. It helps to keep a diagram/photo/drawing to remember. Hope this helps with your decision. After reading all of the posts, I decided to stay with this method. Terre

I live in Houston and built decks in the Houston area for over 20 years. Best answer is to put in a modified French drain under the deck to channel the water out from under the deck. Then fill up the area with play sand,"no clay". This will allow the water to perk out without standing. I did this under Willies Grill & Icehouse on Hwy 6 N and under Adobe Cafe on Hwy 6 S in Sugar Land. If you are using one of these composites on the market, read the fine print. Some do not warranty their product if installed less than 18" above the ground.

I ran into this issue many years ago, there was no solution so I invented one and got a patent on it (see: http://www.freepatentsonline.com/5195281.html). There are no pictures provided, but basically what I did was to insert longintudinally V-folded aluminum flashing to hang on and fit in between the joists. I then put 2x4 "runner boards" atop the joists with minimal screw penetrations (and a rubber washers to prevent leaking). I then attached the decking boards atop the these runner boards (no plywood!). You have to cantelever the deck a bit over the deck support beams so as to allow the open ends of troughs to dump water out. It's relatively easy at that point to catch the water in a spout under the deck cantelever. Further, like I also did, you can fabricate the troughs so that they're pitched to create a high closed end and lower open end. If your using say 2x8 joists you can implement a 7-inch drop. It works, been working at my house for almost 20-years now with no failures. Here is a link that might be useful: Deck Trough Patent (expired)