The lasagna method was not really intended for use with existing permanent plantings.......you really should not significantly alter the soil level around these plants, even on a relatively temporary basis.

I think you are making an big assumption that the soil is nutrient-free - certainly just using a wood mulch, weed cloth and having a high clay content is no guarantee. In fact, it could be quite the opposite. How well are the existing plants growing? If they look good, I doubt your soil needs that much "improving".

FWIW, just a light cultivation of the existing wood mulch (you do not need to remove) into the soil, followed by a decent layer of any sort of nutrient rich mulch - like compost - is likely all you need. The old wood mulch will breakdown over winter (if you keep the area moist), the new mulch will provide nutrients and both will help to aerate and lighten the soil.

Well the soil quality is definitely horrible, perhaps using the words "nutrient-free" was not accurate. I guess its the clay content that bothers me really, as it's a nightmare to dig into and stunts the growth of any plants I try to place in it. Basically DH tried to dig several 12" deep holes to put in some plants and it was nearly impossible, the soil was so hard. And no earthworms in sight...definitely not the kind of soil conducive to gardening. I'm really looking for some way to get at least 6-8" of more usable soil by spring, and maybe get on some regimen for further improving the soil over time.

How would I cultivate the existing mulch into the soil without removing it so I can remove the cloth underneath? Should I add more organic material besides the wood mulch to break down over winter? Also, how high should I pile on the compost over it all?

With a great deal of care you can build Lasagna Beds where existing plantings are, just be sure you do not cover those existing plantings when you are building them.

One thing to watch out for is drainage around the house. Typically builders like clay arounnd the foundation to help move water away from the foundation and landscapers like soil with good drainage so what is best for the plants is not best for the foundation

One of the most persistant of gardening myths is that clay soils are somehow uniformly "bad" - that is not really true. Yes, they may be somewhat difficult to work with (until you know the tricks!) but they tend to be nutrient-rich, retain moisture in dry times and limit the amount of leaching of soluble plant nutrients like nitrogen and potassium due to rain or irrigation.

The primary trick with clay soils is to never attempt to dig deep planting holes -- all you will create is a great deal of work for yourself and a bathtub or bucket for your plants with the next heavy rain. Dig wide but very shallow planting holes and plant high. Use whatever amendments you like to mix with the dug soil to mound up to the top of the rootball. Easy peasy!

Just scrape/rake the wood mulch away enough to remove the weed cloth underneath, then work it back into the areas you wish to improve. And it never hurts to add whatever other organic matter you have at hand. Using compost as a mulch less than 3 inches thick is pretty much a waste of time and money as the material breaks down and disappears pretty rapidly. 3-4" of compost applied this fall or winter should result in some pretty decent soil come spring. FWIW, any organic material is going to break down and shrink over time so any lasagna method intended to "create" 6-8 inches of soil is going to require at least 12-18" of ingredient material to begin with. And that is simply too much stuff to pile around existing plants, careful or not.

Improving soil conditions is not an overnight situation and even less so if working around existing plantings. This is not what the lasagna method was intended for. But by applying organic matter in the form of mulch over a period of growing seasons you will develop a loose, fluffy, well-draining and very fertile soil condition over time.

Always keep any mulch well away from trunks of trees or the woody stems of any shrubs to prevent rot and to discourage hiding places for winter feeding critters like rabbits or voles.

Thank you all for your responses, I have a better idea of how to tackle the situation now :)

"Dig wide but very shallow planting holes and plant high."

GardenGal48, can you specify what you mean by this? How shallow is shallow? and how can I possibly put in any large plants/bushes or even bulbs etc if I plant them in shallow soil? Or should I just avoid doing those things until the soil becomes more usable over time? Will the soil get looser if I keep the area well mulched with some kind of compost?

Also, can anyone tell me where I can get large amounts of compost? I don't make my own yet, and I really need to get a lot for different planting beds, lawns, etc on my property, and I don't know where to find it in large amounts. Or do I just buy the bags from the big box stores like Lowe's etc...?

Instead of doing lasagna why don't you trench compost? Won't change the level but will improve the soil over time. If you have mulch in place just push it aside, bury the veggie scraps between the plants, and replace the mulch. See the current thread on the topic.

I wouldn't bother replacing the wood mulch, that's just a lot of work for no good reason. The only time I've done that is when one garden had the large bark chips which were full of ants. How deep is the wood mulch?

I would remove the landscape fabric tho. There are only a very few legitimate reasons IMO to use that stuff.

I'll definitely look into trench composting, and see which is more feasible.

But I can't leave the current wood mulch because it is 7 years old, has decomposed a great deal and is thus very sparse, and it's discolored. Plus I don't want to mulch with wood chips in the future anyway, as I would much prefer to use compost. Which is why I was hoping someone might suggest a way to get compost in bulk.

There may be landscape supply sources that sell compost, we have them here. However, I would go and look at waht they offer before committing to purchasing any since like "topsoil" compost might be whatever the seller wants it to be. Some of Californias counties have been making compost, out of some of your trash, for years so that might be another source.

Shallow means only a couple of inches. You do not need to bury rootballs in the soil. You should never plant deeper than the soil level of the rootball to begin with and it is typically recommended that one place the top of the rootball slightly above grade under normal circumstances. When dealing with clay or heavy soil, you can (you should) place a lot of the rootball above grade (1/3-1/2 of it) and gently mound the soil up to it. Under some rather severe conditions I have planted the entire rootball above grade (essentially sitting on top of the soil) and mounded and firmed soil around it to anchor and protect. This is a pretty widely accepted horticultural practice.

You can do the same thing with bulbs, depending on variety. Hardly any bulbs will be happy in poorly draining or clay soils so these might be best accommodated by planting in containers until you have achieved the degree of soil condition you desire.

Another alternative is to simply remove the existing plants and mound or berm the soil in the desired area and then replant. You will probably need to import soil for this purpose but you will immediately improve your soil condition, vastly increase drainage and eliminate the issues of digging or working the clay soil. Both good soil and compost can be purchased in bulk from landscape supply yards anywhere. They are all over the place in CA.

This clears up a lot of my questions, Thank You so much!

Lastly, concerning mulching, if say, the top of the rootball is at the soil level, and I lay down an extra 4 inches of compost as mulch, how do I keep from smothering the lower stem? Do I keep the mulch a certain distance away from the stem?

If we are really talking about foundation beds, smothering the plants isn't the real issue. Smothering the house is.

*Whatever* you do, you have to make sure of two things. One is that the ground slopes properly away from the house. The other is that the ground level stays below the wooden parts of the house and doesn't touch. So adding a pile of stuff, which would work fine in an island bed away from structures, isn't the way to go here.

Using compost as mulch may seem like a good idea until you realize that compost is a wonderful growing medium which the weeds will love. One of the purposes of mulch is to reduce weed growth. See the problem?

Since 4" of compost is an awful lot and probably more than necessary, I recommend you use 2" of compost with 2" of mulch over that. You can use your old mulch on top of the compost then a thin layer of new mulch for color. The decomposing mulch will eventually become soil so it's better not to discard it.

I've gardened in clay soil which is like concrete in it's virgin state. Cannot even get a garden fork into it, never mind a shovel. It's more workable if it's slightly moist so if it's watered then allowed to sit a day or two it might be easier to dig. Adding organic material regularly is the answer. The compost and mulch layers will hold in moisture which will help as worms won't be there if it's too dry. They are the best cultivators of your soil and will move those compost layers down deeper.

Would it be possible to remove the perennials temporarily from that bed and till or spade in compost? We've done that to start new beds and it does speed up the soil-building. Still need to add mulch for it's benefits as well as compost regularly.

I have had very little problem with weeds growing in my compost mulch, but I use compost that has went though a hot compost & is still not in the powder state. Coffee grounds compost is in that state from the beginning, but grass clippings & leaves make a great unfinished compost mulch.
The mulch is much like a Lasagna bed topping, as in it lays on top & rots a little at a time, until I till it under in the fall.
I would rather use green grass clipping as a mulch if there are weeds in the path or bed. The grass clipping will kill all the annuals & stop seeds from spouting.