I was thinking the same thing. You can't get rid of bermudagrass without killing the St. Augustine. The good news is the St. Augustine stolons grow a half inch a day in the summer. So killing the yard and starting over wouldn't take long. You say the front yard is nearly perfect so in the perfect areas use some of your yard as a nursery and plug the back. The front will recover quickly and the back will soon be looking as good as the front. The key is using the top labeled amount which could range from 3 to 5 ounces per gallon. Then to use it as soon as you can then in about 2 weeks. You should have pretty much wiped out the back lawn. I would then cut the grass as low as possible then plug all you can. Keep it well moist and then wait. I would think by the end of next year you should have a solid back yard. Good luck.

This is an excellent question with few good answers. The time to deal with the compaction issue is before you plant. Once the plants, especially trees, are in the ground, your options are limited. That is one of the biggest reasons why I am no fan of lasagna gardening. Once everything is in the ground, it is a little late to be going back to what should have been done in the first place. However, not all is lost. A reasonably easy solution to compaction problems is raised beds. Although not very common in Iowa, in places where bedrock is near the surface, you have little other choice if you want to garden. Of course, where bedrock is deep but compaction is a problem, the old solution favored by the British was to double dig their garden beds. In other words, they would remove the soil a full spade depth, set it aside and dig yet another full spade depth. Amendments were added as the bed was refilled. This is a tried and true method that works extremely well. Unfortunately, it is also backbreaking work. Most people are unwilling to expend this much energy and are looking for easier methods. Hence, the popularity of lasagna gardening; which is actually only a slight modification of Ruth Stouts method written about decades before a slick marketing name was given to it. Hey, if you are currently using the lasagna method and are pleased with the results, have at it. It is certainly much better than not gardening at all. However, be honest with yourself and realize that it does have limitations. It is not a cure-all. Quite frankly, one should have enough common sense to realize that if it sounds too good to be true  it probably is. Soil compaction is not eliminated; it is only masked to the uninformed. The way that I addressed the issue of soil compaction was to deal with it when my house was being built  a narrow window of opportunity not afforded to most of us very often. I subsoiled my entire yard to a depth of about 16 inches. (Make sure you call for the utilities to be located, first.) I then incorporated truckloads of compost into the soil as deeply as possible with a tractor-mounted rototiller. And then, most importantly, I kept all heavy vehicle traffic OFF. As I built my garden beds, I incorporated even more compost into those areas and now walk only on the paths. As to the original question of this thread: At my older homes, I eliminated grass by cutting it off with a sharp spade (a sod cutter would work well) and then threw the sod into the bottom of the beds that I was double digging. I further amended nasty, yellow clay by using an old Karen Strohbeen garden soil formula: 30% soil, 30% coarse sand & 30% compost. The soil was tilled and the results were wonderful. I gained supplementary benefits of modified raised beds due to the additional materials and air space. On existing beds, whenever I lifted plants for dividing and/or replacement, I took the opportunity to dig down and create "Karen Strohbeen soil". Of course, at times I hit big tree roots so you just do the best you can. I realize that there are many more ways to do things than the ones I have chosen. Also there are many, many other extenuating factors to consider. For one, I am a big strong guy. If I asked my wife to double dig a new garden bed, she would probably use the spade to double whack me! My preference now is to use my 40 hp tractor to pull a subsoiler. Not all people have a tractor. Some have health issues that demand they use less strenuous methods. For many of these people, lasagna gardening can provide an attractive option. However, sometimes the claims I have heard people making, approach that of a snake oil salesman. Life is full of compromises and tradeoffs  and this is just another example. Every coin has two sides. IronBelly

the stuff in my beds I've been pulling or chopping with the pointy thing this year which works better than my hoe sometimes. But I can only do that because it isn't mulched, didn't get around to getting bags and bags of that and out of leaves. Stuff comes through mulch, too, but not as bad, used newspaper for the border last year but didn't get it down this year. I can't use too much spray because it's expensive and adds up. I've also laid cardboard where I can. I put black plastic behind the garage but didn't cover it all, and it's a mess again with weeds, not much grass there. They say black plastic isn't good for the soil. Yes, I know weed 'n feed and 24D are for broad leaf. I'm stuck with nasty large patches in the lawn that spill over into the garden areas so I want it gone and simply cannot pull it all and get the roots in the lawn, have tried. It's just too hard on my back and so much else to do. Plus it is smothering out all the good grass. This is what you get when you let it go too long.

crabgrass starts out as small clumps - just like shown on last photo. It quickly gets larger and eventually puts out many many seeds. this would be my guess in this case. It is easily pulled (when young) with very thin roots (another good indicator). Recommend pulling before it puts down more seed. Otherwise a weed killer with Quinclorac will hurt/kill it (not sure about Bermuda safe... or not?) Quackgrass on the otherhand spreads by underground roots/rhizomes... can form some dense areas with thick bright green blades (reminds me of st aug. grass)