I hope you are having the soil professionally tested because you will want to know the calcium level, too. Well, here's the situation on Dandelions:

They can and DO thrive in almost any kind of soil, as long as there's enough sun. They seem to prefer more moist conditions, maybe clayey soil, and 'can' be a sign that the soil is acid (which is not a bad thing) OR that it lacks calcium. IF your pH is in a good range (5.5 - 7.5 ) but is low in calcium, you could use gypsum to add the calcium without changing the pH.

The deal with turfgrass is that you need to find out what your pH is and use the grass that is happiest in the soil you already have. There are, for example, different varieties of bluegrass that prefer different pH ranges. Changing the pH on your entire yard and keeping it changed year after year is a PAIN! I think, anyway.

A healthy stand of grass can win the fight over dandelions. Cut the grass as high as it will tolerate to shade out young weed seedlings, but cut regularly.

Are you going to try to renovate the grass that already exists on the property or is it time to have an entire 're-do'? (Sometimes, that's easier....spoken by someone who is also dealing with a long neglected yard.)

I'm not sure what the scope of redoing would be. Is that something that has to be professionally done? The grass that is already there is not dense enough to shade out anything in my opinion. I was planning to reseed once I find out what kind it is and figure out what time of year I can do it in. I've been trying to figure out in what order and on what timeline to aerate, reseed and fertilize (maybe buy worms) as I am sure none of these were done in the 22 years. (The guy who cut the grass for the previous owner told me that other than cutting nothing was done.) I know it is too late to do pre-immergent treatment but I will do that next year. Does corn glutten meal work as a pre-immergent for dandylions? I only keep hearing about it's efficacy for crab grass.

OTOH I am guessing starting from scratch would mean somehow tearing up the entire surface of the front and back yards (which would put a lot of tree roots in danger) and adding a lot of soil to the top. Wouldn't that take tens of thousand of dollars? (as opposed to the couple of thousands or so I'd be willing to invest?)

Thanks for the calcium tip. I am looking up my local extension to find out what tests I can get and how to do it. The soil is dense clay. I'm sure I could shape pottery out of it. Digging through it is like moving rock.

So in short there is not much hope for something to change the environment enough to cut down on the weeds? I can't see us winning the war against them as my grass troops are virtually outnumbered. Perhaps reseeding would turn the tide?

Starting from scratch isn't as expensive as you think. All you really need to do is kill off/remove any existing vegetation then seed or sod. You don't need to bring in topsoil unless you have depressions that need to be filled in. It certainly does not have to be done by a professional. (Although that is an option) But you might not really have to start over.

Altering the PH of your soil won't really help you get rid of the dandelions. It may make it easier for the grass to compete with them, but the dandies won't just die because you raised or lowered the PH. If the PH is really out of whack it can make it hard for the plants to get some nutrients.

Dandelions are perennial weeds, a pre-emergent wil only keep new dandlion seeds from germinating it won't do anything to existing established weeds. Also don't buy worms. If you are really desperate for some worms, topdress your yard with some good quality compost and/or used coffee grounds. If the worms have food, they will come. Also mulch your grass clippings when you mow, and try to mulch up any leaves you get on your lawn and leave them as well. organic matter is the key to attracting worms.

Personally I would spray the weeds with weed-b-gone or something similar(a selective broad-leaf weed killer, it will kill weeds without harming grass) In august, and then seed.(late summer or fall is the best time to seed cool-season grasses) Once you get a good stand of grass going, proper mowing and watering practises will go a long way toward keeping weeds at bay.