We purchased our first home last summer, a 1900 farmhouse located in the north part of Portland, very urban. Apparently the homeowners from back in the day used to dump all their trash in the yard, as when it rains, pieces of broken glass, tin cans, plastic containers... all sorts of stuff starts poking out of the soil, all over the yard. On top of that, we are close to a high-traffic road, and our house definitely had lead paint on it at some point... but we are determined to garden! What are your tips on gardening in such a potentially toxic spot? I was thinking: mulch over all the current weeds and grass, and bring in new soil in raised beds? I don't know if I trust this old garbage-filled soil... and I'm afraid of heavy metals ending up in the veggies, especially because we've got a toddler who is going to end up sharing the harvest with us. Thoughts?
I'm not any kind of expert, but since no one has replied yet...
Obviously, physically remove as much trash as possible. Then, I would get a soil test. Deciding what to do after that would depend on what chemicals I'm actually dealing with.
Best case scenario (an sounds unlikely) there is nothing leaching from the buried trash.
Second best case, the things leaching are chemicals that will be broken down by soil life. Composts, mulches, fungal and bacterial inoculations, cover crops, basically all the things you would want to do for any garden will help support the soil organisms in this work. You might work on this for a season and then repeat the soil test to see if it's helping. I think many oils would fall under this category.
Worse scenario, you have accumulated poisons (like heavy metals) which soil life cannot nullify. Depending on the metal/chemical , you may be able to grow plants that will accumulate the soil contaminates into their tissues and then dispose of the contaminated plants. I know there's been research done on this technique.
Worst scenario, the soil has been contaminated with something that cannot be decontaminated. I would be wary of growing any food even in raised beds unless I was sure they had exceptionally small root systems. I think most plants would extend their roots well into the contaminated soil, even from the confines of a raised bed.
There are alternative short of scraping away and replacing all the soil. You would probably be amazed how much food you can grow in planters. Even fruittrees, if you choose the right variety. I know of one company that sells self watering planters the size of medium/large garden beds. If you look online for instructions, you can probably build your own using less plastic.
In Gaia's Garden he also mentions that there are some fungi that eat leachate in teh ground, and hten you can dispose of them in the way your city prescribes.
In our community garden that's on lightly polluted soil, everybody gardens in big containers and raised beds with lanscaping fabric on the base. I'm not too happy with the set up but am working towards extensive mulching and giant compost bins raised off the ground on top of a pallet. BEst best is just to build up the soil.
Check out garden pool. You can do so much with aquaponics for vegetables. http://gardenpool.org/ When it comes to fruits they don't have good or bad minerals in them just vitamins, just make sure you don't eat too many seeds. So plant all the fruit trees you want.
Nuts/Seeds are usually high in mineral aka both good and bad/heavy metals so, you would be pretty limited.
Fungi will breakdown any bio-available hydrocarbon. And they will also also make lead less bio-available by combining some other compounds with it. So start cultivating your fungi.
Just to add to what folk have said, lots of good advice here, soil test is important to get a general sense of what is going on but it will be best regarded as a benchmark. As an urban lanscaper of several years I can tell you that every cubic foot of soil you test is going to give wildly different results. It has been moved, removed, and dumped where it lies.
Fungi, particular ones that grow mushrooms are potential remediators for your soil. Dispose of the mushrooms away from a food area and save some for taking tissue samples of flushes so you could monitor the progress metal removal. Tests can sometimes be done cheaply through a local community college or university extension.
Organic matter in the form of compost will help to bind some metals in the soil. Some jobs I've laid down mats of mycelium with successional species and built raised beds on top. Others I've used the not-so-popular heavy gauge landscapers fabric and mulched chips and raised beds on top. I second the aquaponics consideration if you can invest in the temp control. You will get a lot of production from it and there is no need to mess with known hazards.
Greetings from a fellow Portlander with little kids, an old lot/home situated near a high traffic area, and a flourishing permie oasis!
I agree with prior posts about soil testing first, before assuming the worst. There's a definitely a possibility that most of it is unsightly but mostly harmless. We recently tested the soil in our back yard (where we mostly have fruiting trees and shrubs in the native soil, the front is raised beds with imported soil) with Lead Safe America. Their office is in inner SE; its a pretty good deal- I believe a local lab donates their services for a $5 donation per sample to Lead Safe America. So, its definitely a win-win, getting your soil tested for Mercury, Lead, Cadmium, and Arsenic while also making a donation to a great nonprofit run by a passionate, driven local mama. The drawback is that they don't test for petrochemicals.
Of course, all lots vary, but even our lead levels weren't terrible (well below EPA standards, just a touch above California standards); our mercury/cadmium/arsenic levels were nearly undetectable, despite being in the armpit of I-84 and I-205 and having 82nd ave 3 houses away . Also, we've been getting both of our kid's blood levels checked routinely since about 12 months old and they have always been under 5, so that's reassuring too.
Provided your tests don't reveal something awful lurking in your dirt, I'd get a load of woodchips (www.chipdrop.in All the chips you could want, free or nearly free!) and mulch over it all, then fashion some raised beds and get a load of good garden soil. I think its worth the investment to start with good, fertile soil anyway.