Using Allelopathic tree fall as a natural "roundup" for lawn conversion???

Does anyone have any experience with using allelopathic leaf fall as a natural “roundup” to kill grass? I have a large lawn above a leech field that I am trying to convert into a natural meadow (with shallow rooted + drought tolerant grasses and wildflowers) and want to kill off the grass naturally prior as I don't want to dig up too much above the leech lines trying to remove the grass. I have a BUNCH of California Pepper Trees along with all the leaves that have fallen over the years on another part of the property, and I know they are allelopathic, nothing grows underneath them... So would using the leaves piled ontop of the grass during the winter mixed with rain kill off the grass? Also, for how long would the toxin in the leaves last in the soil? Would that be futile to try planting wildflower above it later?

In most cases the allelopathic chemicals in plants will be broken down by natural processes within a year. When googling the California pepper tree I came across gardening articles particularly recommending it as a good compost ingredient. I suspect they wouldn't have a long enough chemical effect to kill the grass. If you can pile them deep enough they would still work well in a sheet mulch. Most trees with allelopathic reputations are actually killing competitors through this mechanical process.

I've had good results converting lawn into garden beds by sheet mulching with thick layers of wood chips (think 12 inches or more) and then hand pulling the few bits that managed to grow up through that. Grass growing through that much mulch is very easy to pull. It's not an instant process, but it works well. If you have tree trimmers working in your area (or landscapers who trim trees) you can try approaching them to see if they would like a free dump site. If you are willing to accept a whole truck load, they are often happy to avoid a trip to the dump and the associated fees. Landscape trees are less likely than most other plants to be sprayed with noxious chemicals.

Casie- Thanks for the info! That seems totally doable, just worried whether that would be too much extra weight on top of the leech field? I'm new to the whole leech field thing, but I was reading somewhere that you have to be careful with raised beds/extra weight on top as it can collapse...Although its probably minimal with just wood chips...

Do you by any chance have a link to that research on pepper tree being good for compost? I feel like I've been seeing the opposite, but am welcome to new info because I have TONS of california pepper tree leaves to use up! Thanks again!

It was actually from a gardening article. The man who wrote the article replied in the comments http://www.patwelsh.com/trees/california-pepper-tree-or-mexican-pepper-tree/

In my area people are always saying oak leaves and pecan leaves (which are related to walnuts) shouldn't be used as mulch for the same reason. I pile all the leaves from my pecan trees on one bed every year and add bags of oak leaves several inches thick onto others and my plants seem perfectly happy. My only complaint is they break down faster than wood mulch and so I really wish I had twice as much by the end of every growing season.

There is a tree (rocky mountain juniper) which does have allelopathic wood chips here. My mother took the time to find actual research studies on that and found it only affects some plants, and after one year there is no longer any effect. Just like most other toxins in the soil, soil biology will break the allelopathic compounds down into more basic nutrients that don't harm the plants.

hau Allie,  " I have a large lawn above a leech field that I am trying to convert into a natural meadow (with shallow rooted + drought tolerant grasses and wildflowers) and want to kill off the grass naturally prior as I don't want to dig up too much above the leech lines trying to remove the grass. "

Unfortunately shallow roots are contrary to draught tolerance, most draught tolerant species have deep roots.  

I agree with Casie on the mulch/compost ideas and components.  

A leach field usually has gravel around the field lines and they are normally a minimum of 1.5 feet below the surface, so really you don't need to worry a lot about the weight of organic materials being spread over the area.
Most of the cautions about raised beds and their weight could be mostly considered bunk if the field was laid out and put at the correct depth. The easy way to test that is to dig a single hole and locate the field line depth that way.
Our septic system has field lines buried 2 feet deep in a bedding of gravel, we have driven my jeep over them a couple of times with no collapse. One way to locate a field line is to look for where the soil settles (there will be a depression line showing where the pipe is) usually there is a slight sinking if you look for it.

The easiest methods for getting rid of grasses are to keep sunlight off and heat in, this will effect a kill of the plants and any seeds that survive can be shaded out by a thick planting of

What type of grass is it?