You are pretty much doomed at this point. The only thing to do is wait for the weeds to germinate and then remove them before they make seeds. Then repeat and repeat for a number of years. Most people don't bother to do it. Eventually, if the weeds never make seeds again, you will have a lot less weeds, but you still have to be on it constantly. There is no killer that will do it for you. The so called years one will only mess up the soil. You could use round up every two weeks for a few years, but again this is not very healthy for the garden.

Maintaining any garden means constant attention, there is simply no way to keep unwanted plants out without that. Plastic is probably the worst "weed" barrier there is and should be removed. Mulches, if deep enough can be effective plant growth barriers, for a while, but those unwanted plants will grow in that mulch if it too is not maintained.
There are some pre emergent controls that work for a while, but not forever and there are plant poisons that will kill off what is growing there but will not prevent seed germination. But both can be quite expensive to use as often as necessary.
When you leave someone will need to be out there doing what you have been doing.

one good trick is to get some newspaper, and put it down like the weed fabric, then put mulch on top. water well before you do this and when the weed seeds sprout, they will not be able to get any sunlight and die. The paper will decompose in a years time. You can get paper for free or go to a local print shop and ask for some old make ready sheets, just make sure to get UNCOATED paper. Inks these days are soy based and will not harm your plants/trees. It's fairly simple to do, and a heck of a lot easier than spending HOURS pulling weeds!

There is this thing called a lawnmower. Most people think its only purpose is to cut grass. They do not recognize it as a superhero in the fight against the temperate jungle.

You don't describe anything about this garden, but if it can be cleared out enough that a lawnmower can get in there, then the ongoing maintenance becomes less than five minutes more when mowing the lawn.

My next door neighbor hires illegals to clear out his yard every six months or so. But, if wanted something pretty that was be nice to spend time in, you have to do some work.
How to hire illegals, and I disapprove totally, but I want to draw attention to something that is wrong. Go to Mission district in SF, drive around Army Street, see them standing there, open car door, have them get in.

This post was edited by tropical_thought on Fri, Jul 11, 14 at 10:50

Mulch.

Thank you all for your advice. I do have before and after pictures of what I've done but they are too big for me to post on this site. I've even tried compressing it and it's still too big.
I don't think my parents want a garden there. They have one elsewhere in our yard. At this point they just don't want anything growing there.

Here is a picture of where I'm at now. It used to be so overgrown that I have friends who didn't know anything past the first wall existed.

Here is the before picture

Is that a wall? It really does not look so bad. If you don't want anything growing use round up every two weeks, but the weather should be at least 70 degrees without any rain.
I see like a nice lawn there, I don't know why you would want to use round up on that.

This is what it looks like from up there. I tore all that plastic stuff out (which was a major pain in the butt). There are some pretty major stumps up there. Like stuff that is at least 5" in diameter. I'm not really sure what to do with the bigger stuff

Ah yes, that does look much worse. I would suggest removing plastic then a heavy layer of mulch, like wood chips, followed by using round up on each weed, that makes it's way to the surface. Otherwise, the job of just of spraying round up would be huge in, itself. Since you don't care if the soil is robbed of nitrogen with the wood chips, you can try to call a tree company, often they will delivery to your house piles of ground up tree wood. You will want it to be really thick like hopefully six inches of wood on there. The less wood the more likely weeds are to sprout up, and of course, in time you have to replenish the wood. But, once I had some large bark pieces I bought it a bag and it lasted years. The larger the pieces the longer it will last. Don't use something small like microbark.

That stuff growing may need round up tree and brush killer. It's not just weedy grasses, but something like ivy? If it's wood like or thick vines, it takes a different kind of round up. Sometimes I get smart and mix the two together in deadly combo spray bottle. I buy the concentrated and mix it in a spray bottle, that saves money.

A lower effort way to deal with small stumps is to hack them as low to the ground as you can and then cover the residual stump with dirt for a few years, It should give you a small hump. The stump will definitely rot away under that condition and the rot might be hurried along with the addition of a hefty amount of nitrogen. I prune such stuff with a sawz-all type saw with an old 12 inch demolition blade mounted (because of the rocks). Better than an axe.

Do NOT use the "prevents weeds for a year" stuff because they often kill everything because it's a soil sterilizer. Read the label.

The black plastic was supposed to prevent weeds, but it never does ... horrible stuff.

What everyone is saying ... remove as much of the plastic as possible, lay down a biodegradeable blocking layer (cardboard, multiple layers of newspaper), topped with a thick layer of mulch. Arborists will perhaps be willing to drop off a load of wood chips for free.

But the area WILL need regular weeding, maybe every month or so, or it will regrow. You can try using a "pre-emergent" to prevent seed sprouting, but they don't always work.

========
To prevent brush regrowing .... take a small foam brush and a small container of concentrated Generic Glyphosate (Walmart sells it as "Eliminator" for really cheap). Cut the stumps as low as possible and dab on the herbicide.

Pre-emergent is called Preen, I tried it before, but it only last for less then a few months and they costs run up quickly and it does not prevent all weeds, many of them just laugh at that Preen stuff.

Also check Craig's list for free mulch, because I got a lot of wood pieces from a family that ordered too much from a tree service. Go to Craig's free stuff part and search for mulch. But, if you want to buy large western bark in a bag, which I also did once, it lasted for over 10 years, with no need to reapply. It depends on how thick the bark layer is and how much it rains. If it rains a lot the bark will decay faster.
The all kill stuff did not work either, as I can recall, I have tried it all, or maybe I stopped using it. It was called Troy or something like that and it was in a can and did not seem to work. It was something like remove all weeds first then use this stuff. It did not work at all. If you are going to remove all weeds, there is like no reason to use it as the weeds are very tough. It would kill off nice plants, but weeds are like super demon spawns. I read all the these tips like use boil water or vinegar and none of them affected the weeds.

it was said above... MULCH ..

i will repeat.. MULCH ...

and in case you didnt get it.. MULCH ...

your battle is two fold ... destroying what is there ...

but also.. preventing in the future ...

most seed is air borne... even if it comes out a birds butt .. and it requires that is actually touch the soil to germinate ...

one of the purposes of mulch.. is to cover the soil surface.. so weed seed doenst get to the soil ...

it will also soften the soil below.. so weed removal is easier .. in the future ...

the plastic is a nightmare... as you now can appreciate ... if you were going to be gardening there forever.. i would say.. take the time to remove it ... but i dont know if i would take the time.. in your circumstances ...

if you missed it.. MULCH ....

ken

The walls AND the roots of what you pulled up were holding up a lot of soil weight.

So depending on the original engineering and what time has done... Are all the water runoff from above exactly the same as when this was built ? Slopes of roadways , construction and neighbors land changes happen all the time.

Is that black plastic or porous weed barrier ? If black plastic it may have been installed in an effort to force more water to run over and down, rather than all go into the soil and increase the pressure behind the walls.How were the original, behind the wall drains included and are they still working well ?
Assuming the house is below, how is it set on the land if suddenly there's a wall of water. Will that water be directed away from the home ?

If the wall starts to shift, I can see the whole mess coming down, followed by the trees tipping and falling on top of the whole mess.
Worst case.. how would that affect the downhill neighbor ? And exactly what is covered by your homeowners insurance policy ? If these answers are not up to date, this is a good opportunity to review .

If it were me I would be more concerned about preventing a landslide when the weather is just right, rather than appearances. Really a specialist review at this point would be money well spent.

In the meantime how about identifying the bits and bobs that are left. Knowing the weeds vs. the plants could help you know which were planted to hold up the land, and possibly let those grow back as the original design. Then it's a matter of keeping on top of the unwanted species.

This post was edited by plaidbird on Sat, Jul 12, 14 at 17:48

I would suggest you google how to solarize the soil and skip the Roundup.

If your parents have neglected it for 15 years, maybe they aren't into gardening!(GASP)
Perhaps they should think of moving to a place that is low intensive maintenance , have it landscaped for the Low M, or move to an apartment, where there is NO work at all!
Though you have great intentions, will you be around to maintain their yard? Do THEY want to maintain it? Nancy

Not really, about the move out, my of neighbors have yards like horror shows. I don't like it one bit, but I would not say they have to move away because of it. In fact, I have a huge problem, all the yards are touch each other and weeds growing from their yards are more work for me, then my whole entire yard, because I have a system down.

There is a lot in this thread. I recommend the OP check out the link below before going crazy with sheet mulches like cardboard or newspaper. Arborist wood chips and a bunch of them are the best suggestion.

With regards to herbicide, a preemergent is a good way to reduce the weed seed load on disturbed soil. By pulling out the weed barrier (good move) you will bring up lots of weed seeds. A preemergent will cause many of them to rot away. Some will pop up still, but those can be controlled as they come up either mechanically (pulling, string trimmer) or chemically (glyphosate etc). On freshly disturbed grou d like this, I like to perform a few grow/kill cycles to really get rid of the weed seed load. The OP mentioned year long herbicide. I am wondering just what was actually laid down. Without knowing that we can't really say what the long term efect of that action will be.

One of the best ways to keep weeds out is to heavily shade the ground with large shrubs like the ones that were removed. An open empty patch of dirt is not going to stay open and empty for long without effort. If you want to keep this low maintenance you will probably want to replant with something.

Here is a link that might be useful: Horticultural Myths

cardboard, layers of newspaper mulch. wood chips
all excellent

personally,, i would add a couple of fruit trees.
maybe section off an area to add some herbs, or ground cover plants. even a shade tree

To me, all that extra yard is something to exploit, not a nuisance
what part of the country are you in ?
How many hours of sun does it get ?

See, the gardeners here can't grasp the concept of not wanting anything. Even if you have trees, etc, it still will get weeds, still will be work to do. My neighbors laid down concrete on one side, but they still have area of dirt, because you can't have all concrete, there is no drainage that way.

I just remembered Astroturf tuft is expensive, but it drains because they put gravel underneath, but it has to be replaced every 10 years. Overall it just costs too much unless you want to have kids out there playing on it.

This post was edited by tropical_thought on Tue, Jul 15, 14 at 10:53

Thanks for all the advice. To be quite honest, I'm a little overwhelmed by all the information provided. Maybe even more than the task of taking care of it all!

I will definitely have to look into some of the ideas and do my own research. I'll talk to my parents to see what they want to do with it. Thanks again for all the help

Second the mulch idea, but Nature will simply not leave ground bare. Things will try to grow.

Is it accessible to a lawn mower? Why not plant grass there and mow it? At least it will be under control. Or you could reduce mowing by putting in some kind of slow growing, low ground cover plant that would shade out weeds. The idea is to grow something there to prevent nature from filling it with weeds, shrubs and trees.

Any type of grass, even weed grass will allow other weeds to break into the area, and even things like blackberries and English Ivy. If you really wanted no work, your choices are heavy mulch with some spraying of round up from time to time, concrete, no work at all, or astrograss, no work, but must be replaced every 10 years and expensive. Hiring a clean up service to come every 6 months, you can find them on Craig's and they sometime put flyers in our mail boxes. Its called yard clean up, they don't garden, they just pull it out and haul it away.

Weeds and other stuff might sprout, but if it's mowed along with the lawn, they are not going to get far. I don't see a lot of weeds in their lawn in the pics, so if they make it part of the lawn, it will look the same.