Another google map view. His house is to the right of the field.

Ground level view of his backyard facing that dandelion field to the west.

And the link to the other pictures again: http://imgur.com/a/znctg

It seems all you can do is wait for the dandelion field to someday be developed. Fantastic open space, though it's not being maintained adequately for the benefit of your gardens. Are there any suppressing ground covers that do well in your area that you can use. I use archangel lamium where I live but hear its invasive in wet climates. I do have dandelions that pop up here and there but not like your situation. Oxalis is the bane of our existence. I can manage my dandelions by popping the flowers before they go to seed. I'm in the woods on the edge of protected parklands so we have an issue with an invasive thistle. Having your garden mowed regularly is the only other thing I can think of. So sorry you are experiencing this and I wish I had a better fix for you.

Hi sandturtle
I just moved to a very similar layout/issue (green space behind us, Ontario anti-pesticide/dandelion army to fight...)
I’ve just begun growing Virginia creeper and English ivy up the chain link fence behind me.
I know they’re invasive, but in a couple of years they will provide privacy/wind/dandelion block, and English ivy will keep its leaves somewhat in the winter, and Virginia creeper goes bright beautiful red/orange in the fall.
I might add some annual flowering vines into the mix and just let them duke it out over the fence, and if any spill into groundcover, great.

Me neighbour isn’t a gardener and just has black privacy screen put up on their chain link fence to keep the weeds from blowing into their yard, which they say helps quite a bit as well.

And if you really want, if you look up the special ingredient in some of the weed killer from the US, there are plenty of sites that still ship to Canada :)

- Chemical approaches are off the table (no weed killers or anything like that. The safe alternatives such as boiling water etc, are basically a no-go as well due to the sheer amount of dandelions he's dealing with and the assumption that there are probably countless dormant seeds just waiting to sprout up at any time).

dandelions are easy to kill with a selective herbicide that won't also kill the lawn. but there are so many dandlions there that I would spray it all dead with roundup then reseed fescue if that'll grow good up there, and then keep the fescue mowed tall 4-4.5" will help shade out dandelions from sprouting. but I'm sure you'll still get more dandelion but those can be selectively sprayed and then reseed again and get a thick lawn. the dandelions are only like that for a couple weeks in Spring and Fall time though, no? and the rest of the year it's almost a groundcover I don't see a problem with if he doesn't.

I don't like using chemicals but they work. and can be minimal if done right. oh edit, I think canada banned chemicals, I approve... you can till it and reseed but till it finely because dandelions have a tap root like a carrot that will regrow even if cut in half, you gotta really grind them up small.

can also keep it all organic no chems etc and juice the dandelion leaves they are extremely healthy. they were brought over from europe I beleive as an accent to lawns on purpose now people think they are the devil.

yes putting a solid fence will help wind-blown seeds but not %100.

- so making the transition into a complete rock garden wouldn't be that big of a change on an aesthetic level).

rock gardens especially small rocks as someone mentioned, dirt will makes its way between the rocks and then weeds form in the rocks can become a nightmare. And fabric usually sucks and makes it worse the roots go right through and try and pull roots pulls the fabric too. plastic probably better but still can get weeds. unless you put weed preventer pre emergent (chemicals sitting there the whole year no thanks) then weeds will grow.

some places just seem to get lucky and rock beds don't get too weedy even after decades but some places get real bad real quick even with crabgrass.

2. Same complete removal of the grass/ weeds, but then buying massive quantities of hardy groundcover plants (he was thinking Irish moss or related) and hoping they are all able to catch/ spread really quickly and are able to outcompete the dandelions for occupancy of the yard space

I would suggest this also groundcover. find what works great for that zone. maybe also plant a shady tree(s) should help slow growth of dandelions and groundcover might prefer shade but I personally prefer a full sun yard.

maybe build a canopy for a grape vine over the whole yard.

maybe get a cheap tiller and till a garden each year plant veggies and stuff. mulch in between the plants with grass clippings. it's work I don't know if willing to do or if a garden 'fits' in that neighborhood but it's an option.

or plant more and more shrubs, hedges, large ornamental grasses make a sort of mystical maze of dense plants.

or concrete over it all if allowed. patio needs re-do polymeric sand I see bunch of weeds pavers need maintance vs concrete pad doesn't.