The mix of grasses you are dealing with make your approach problematic. It is unlikely that you actually got all the roots of the bermuda grass or St. Augustine /Kikuyu grass, and the crab grass will quickly come racing back from seed next spring. You may not want to hear this, but I would suggest that using herbicide like round-up, alternating with several weeks of irrigating to encourage new growth, and repeating several times while it is still warm, will give you better results than what you are doing now. It is nearly impossible to completely kill bermuda grass without using herbicide. Crabgrass will also always come back from seed unless you pretreat the soil by using a pre emergent to keep the seeds from coming up. At a minimum,if you're opposed to using chemical methods, I'd suggest pulling off the plastic covers and watering well to get new froth of all the weed seeds and remnant grass rhizomes and carefully dig them up thoroughly or hoe them off for the shallow rooted crabgrass seedlings. It's not easy to really get a clean slate when removing your mix of lawn, and your methodology is almost guaranteed to fail to give you a weed free starting point._

thanks, bahia! i know... i'm feeling very pessimistic.... my dad had a blood cancer, so i'm EXTREMELY reluctant to use chemicals. i just won't do it (stubborn, i know).

if some of the grass survives, will it completely infiltrate our newly-landscaped yard? or will it just be annoying occasional patches of grass?

If you don't want to use chemicals and want the best possible solar kill, I would replace the black plastic with 2 mil clear plastic. This is very thin, but will allow the deepest penetration of the heat needed for a solar kill. Unfortunately as bahia says some weeds seeds you will not be able to kill this way, no matter how well done. Al

Bermuda will infiltrate your new plantings and you will not be able to pull out the bermuda without digging up your new plants. It would be such a shame to have your beautiful new yard become weedy.

If you really want to go au naturelle, take up the plastic, get a 1/8 inch shaker screen (like the ones archaeologists use) and dig down a shovel's depth and put all of the soil through the screen, pulling out the stolons from the kikuyu and bermuda. Then water and weed, water and weed, until no more comes up. It can be done, it's just labor intensive.

Even if you use Round-up, you must use it exactly according to the instructions to get good results; and if memory serves, the label says to apply the first treatment in Spring and then again two more times for Bermuda.

Or, if you have enough money, you can have it scraped away with a Bobcat and new clean topsoil brought in.

Good luck, you have taken on a big project and it will look wonderful when you are finished.
Renee

No chemicals means a lot more time and hand labor to combat regrowth of weeds and grasses. The black plastic will be worthless, and short of removal of the top eight to twelve inches of soil with a bobcat, your only other option is alternating several weeks of heavy watering to encourage regrowth of grasses and hand digging/hoeing off of the crabgrass seedlings. Crabgrass seed is particularly persistent, and as a warm season weed, you should probably repeat this all the way into late spring of next year if you won't use any herbicides or pre-emergents. Your mix of lawn grasses will rather quickly be an out of control mess within your proposed new landscape. Sorry to be so negative, but just telling it like it is. The lasagna mulch technique would give you better control, but it needs just as much time and the mulch would need to be at least six inches thick. You would still need to be very vigilant as you plant next spring if you can be patient enough,as you'll still have residual seeds exposed to light as you plant new things, as well as residual Bermuda/Kikuyu /St Augustine grass to deal with, but lesser quantities than with the black plastic.

Agree with bahia - we did the 3x process with watering, letting the Bermuda grow, then Roundup (bought a backpak sprayer for our 1/6 acre lot). The first time kills the top, the second time about half as much grows back, and the third time gets the last few stubborn patches.

Bermuda tries to creep in from both sides from our neighbors' yards, but so far (since 2002) we've been able to keep in check the few rhizomes that stray in, because it was totally eliminated.

One neighbor dislikes using chemicals so she has tried just weeding/mulch. It does not work. Bermuda's in almost everyone's yard, and the seeds are always landing on nice open ground where they can sprout.

Our lawnless property is all cottage garden-type beds, and must be hand-weeded. I've had Bermuda seeds sprout underneath the heaviest, deepest shrub shade where no other weeds were able to survive - a good 20' away from the nearest lot!

The link below comes from Tree of Life Nursery. They offer classes on how to replace your lawn with native plants. There is a PDF document you can download and read. It may give you a few ideas. Bermuda grass is tough. I'm still pulling some out after 5 years.

Here is a link that might be useful: Kill Your Lawn

I'm still pulling bermuda after 12 years, though I have it close to irradicated--only one bit has come up so far came up this year. The roots can go 3 feet down, and if a root remains, it can come back from that root.

If you are extremely concientious about pulling it out as soon as you see it, for years, then you can get rid of it. You must be obsessive and dedicated.

You could try repeated applications of industrial-strength vinegar instead of round-up. Do not get the vinegar on your skin, because it can burn.

Western Redbud is one seriously over rated native tree. I'm getting rid of all mine. It reseeds everywhere and the seedlings are very hard to pull out. A stem borer is killing them.

I second Calistoga's suggestion on clear plastic. You also need to make sure the edges are sealed well. Water prior to putting down the plastic so that the sun will solarize the soil. You want the temperature to rise and kill seeds, bacteria and bugs in the soil. Then I would uncover and water to let any seeds that lived to be sprouted and killed with roundup. I removed my lawn, followed these suggestions and never have had a weed problem.

I also layed all the pieces of grass upside down on the area and made raised free form beds.
Penny

I'm with bahia and hoovb on this. I prefer to stay away from using black or clear plastic because not only will it kill plants and weeds (and barely touch the Bermuda), but it will annihilate all your soil microorganisms, earthworms and other beneficials, leaving you with with dead soil. Not something you really want. I rarely resort to Roundup, but this is truly the "least of all evils" with Bermuda. Then use a per-emergent to prevent the seeds from sprouting. Hoovb suggested using industrial-strength vinegar (which is pickling vinegar or 10% acetic acid), but it does burn (ask me how I know this). It works, but not quite as well as Roundup. You'll need probably 3 times the number of applications, and it's nasty stuff to use in a large application. Better for using as a weed killer in your concrete driveways or pavers. Roundup is the way to go, protecting nearby plants from overspray. Just as bahia has recommended. I have to do this with a pretty large area of Korea grass, which is equally nasty stuff, and is overgrowing everything on this part of my side yard. I'm going to replace it with dwarf variegated Mondo grass in little bunches. Much more manageable and will look so much neater.

Patty S.

thank you everyone for your advice and suggestions.

one of the issues that has me most concerned is the killing of the micro-organisms and bugs in the soil-- you're right, I don't want dead soil!

my husband is out of town this weekend, then I'm out of town the next two.... perhaps we'll pull up the black sheeting the second weekend in Sept and see what we've got, pull up any new weeds and begin a new pulling/spraying w vinegar regiment.

i'll keep you posted!

Black plastic doesn't work well for solarizing soil because it absorbs and transmits heat, instead of allowing it to pass through and trapping it. If you are determined to do this without pesticides (which, ironically, are usually far less damaging to soil microorganisms than solarization) I have used one more method (I got the idea from an everglades reclamation project) with good results:

1.) Trench the soil along all of the hardscape surfaces adjacent to your planting area. 2.) Call local Arborists and ask them do dump mulch either on the planting area itself or some place nearby and 3.) Spread the mulch to a minimum depth of 6" over the entire area (9-12" is better) 4.) Water the entire area and do nothing for about a month 5.) Plant through the mulch, being careful not to get soil on top of the mulch (dispose of any extra soil from your planting holes elsewhere on your property). 6.) Be vigilant for Kikuyu Grass (probably what you are calling "crab grass" and a weed 1000x worse than Bermudagrass ever thought of being) popping up around your new plants.

I only recommend the above described method for minimally irrigated areas (I give the area a deep soaking once in the fall to jump start the growing season, occasionally irrigate during dry spells over the winter and then another deep soaking after the last of the rains in the spring - generally by the first of May). I usually mulch the area once a year, after I've done my summer pruning (which largely consists of weed-whacking the dead stalks of some of the tougher leaved South African bulbs (Watsonia and Chasmanthe are particularly annoying in that regard).

Ryan

I've killed off most of my lawn using thick layers of newspaper or cardboard and heavy mulch. I've not had any trouble with crabgrass or bermuda coming back, but I left the mulch on from one summer to the next. That's a long time if you're itchin' to get your landscaping in, but I avoided using chemicals and the grass has never grown back.

So, we've decided to move forward on using mulch to kill what is left of our lawn, and it seems we might even be able to get free mulch delivered from the Los Angeles Department of Sanitation.

However, part of our landscaping plan for the front yard involves putting in a wooden beam wall in one corner, and therefore shifting some of the soil from throughout the yard to fill in that particular corner (and level out the rest of the yard on that side), and we are also considering creating one or two other small hills/slopes that would involve either adding soil or shifting soil already in our yard.

Since we actually would like to lower the level of the soil in some places to be able to add a few inches of decomposed granite and match the level of the sidewalk, it seems to make sense to use the existing soil.

So, finally getting to the question: are we better off building our "retaining" wall and hills first, and then mulching over it, or does it matter? It seems like disturbing the soil after using the mulch method would be counterproductive.

You want to do any grading first for two reasons: First, one of the main reasons for using mulch is to inhibit weed growth, which means the mulch needs to cover the soil, not be mixed into it; the second reason has to do with the nitrogen cycle. In short, the wood chips in mulch are made up of cellulose, which is essentially a sugar polymer: H, C, O. Its breakdown is facilitated by microorganisms which need a lot of Nitrogen. Since they won't be able to get it from cellulose (which doesn't have any) they will take it from the soil. If the mulch is on the surface, there will be a nominal amount of nitrogen sequestered by bacteria and actinomycetes only at the interface of the soil and mulch. If the mulch is mixed in, this sequestering will occur throughout the soil, leaving very little for the plants. This is only temporary of course, but will persist until all of the cellulose is consumed which will take a while.

Think for a minute about free mulch. Is it thoroughly composted, or fresh chopped plant material?

How do you know it's not full of weed seeds and/or diseases?

I think you are correct, SoCal, but only for mulch that is composed of bark, wood chunks, twigs and other large diameter wood products. If Lynne is getting a more finished compost with a reasonably high % of humates already released by microbial & fungal action, which is what my experience is with LA Co compost from their San Pedro yard, it's a 60-80% finished hot composting material, with a significant amount of partially digested large diameter wood still in the mix. I find that mix is a little prone to clumpiness and reduced O zones unless mixed with some native dirt and washed sand (5-10%, each) for better mulch soil structure, but has lots of available N, especially when soaked with a fish or seaweed meal solution.

If she's just getting green/brown tree limb pieces from a chipper delivered off a county crew's worksite, you are, of course, absolutely right.

You're right dicot, I misread (I've never used composted material for mulch), that does still leave the (to me) more serious issue of the lack of a weed barrier though.