Is it safe to eat--next summer?

September 12, 2007 7:15 PM

Can we safely grow some vegetables or herbs in soil that that apparently has had copious amounts of pesticide, herbicide, and fungicide applied to it two years ago and probably also for several years prior?

We rented the place two years ago from the owner, who apparently believed the backyard "garden" should equal "mausoleum." He had several very nice bushes and shrubs going, but after talking to him we found out that he bought these full-grown from the nursery (and had done so every spring for several years) because "they don’t last long." He then showed off his extensive collection of chemical pesticides, herbicides, and fungicides, and said he would leave them for us, just in case of bugs or anything. If the rest of the housing deal weren't so good, we would have run away at that point.

After our two years of organic care, the yard seems to be coming back to life. I actually saw an earthworm! This season we grew a few heirloom vegetables and herbs just to renew the seed. They really didn't seem all that healthy compared to their parents, but I'm not sure if that was the age of the seed (about 4 yrs.) or the condition of the environment.

How can I determine if it's safe to plant edibles here?

posted by Anisoptera to home & garden (24 comments total)

Define safe. If it were me, I would do it. Most of those chemicals wash away pretty easily. That is one of their downfalls. Two years probably safely washes all of them away from the root zone. However, some of them are designed to be hydrophobic to prevent the rain from washing them off. Those won't wash away so easily. To be really safe, scrape and replace the soil to a depth of about two to three feet in the vegetable garden.
posted by caddis at 7:22 PM on September 12, 2007

Do you have a state ag extension? If so, most have a gardening program and they can help you, usually for free, to learn how to rebuild abused soil.
posted by melissam at 7:28 PM on September 12, 2007

I'd also recommend building your garden up, above the soil in the backyard, and using all new soil. There is a method for doing this that has some good ideas, some kind of wacky ones, called Square Foot Gardening. You can google it and see the guy's website. It's an organic form of gardening that works regardless of what kind of soil you have, because it doesn't use that soil. I personally don't like the look of the gardens that result, but I do like the rest of the plan. And it would definitely be safe, because your plants wouldn't be growing in soil that had been so abused.

Good luck, and thanks for caring about the soil in your yard. The world needs more people like you. (Or at least, it needs the people already here to feel and act like you do.)
posted by Capri at 7:32 PM on September 12, 2007 [1 favorite]

I wouldn't grow edibles without having your soil tested (possibly by that ag extension). This isn't exactly your situation, but You Grow Girl has 1"2 reasons why I don't Grow Edibles in My Street Garden."
posted by Airhen at 7:36 PM on September 12, 2007

I would have it tested before I ate anything. For organics and heavy metals (make sure you get copper).
posted by fshgrl at 8:42 PM on September 12, 2007

You can put your square foot garden in some fairly attractive boxes, rather than the prefab vinyl things that some people use. Also, less weeding.
posted by mecran01 at 9:10 PM on September 12, 2007

It's so easy to grow your veggies in either a raised garden (along the lines of previous comments) or just flat out in containers, I wouldn't even try using the soil with that kind of history. A previous landlord of ours would turn up randomly and spray the gardens with roundup and other stuff, so we went in totally for container veggies and it worked out great.

We've grown a lot of things in pots of various sizes. Shallow washing tubs from a plastic shop only cost a few dollars and are great for lettuces, cress, radishes, etc. Just need to stab a few holes in the bottom. Alternatively you can usually find wooden seedling trays at a plant shop if you want to avoid plastic. Courgettes, pumpkins, gerkins, etc can be planted straight into a hole cut into a 50L bag of potting mix (cut a cross rather than a round hole). Larger pots can be pretty cheap if you don't care how it looks (plastic or plain terracotta are generally cheapest) and are great for root vegetables (fine potting mix makes nice long roots) or more shrubby things like cabbages or capsicums. Big plastic or wooden tubs are fine for growing tomatoes as long as you stake them, keep them out of the wind and water them daily. We have a whole orchard of miniature citrus in pots we take with us when we move house (OK, five citrus plus a fejoia but it feels orchardish). Adequate watering and fertilising are the main issues with container gardening, but it sounds like your thumbs are green so this will be fine.

Definitely keep up the good work with your garden. I'd be planting non-edible things and planting things that maybe can help the soil (um, legumes maybe?). But you don't really know what has gone into that soil so why take the risk putting it into your diet?
posted by shelleycat at 10:19 PM on September 12, 2007 [1 favorite]

Take a look at the guidelines for organic certification, which requires that the land has not been treated with prohibited substances for at least three years.

I think it is possible to be overcautious about these things. Consider the benefits of having lots of fresh vegetables to eat, along with the exercise and satisfaction of growing them yourself against the small, ill-defined harm of eating vegetables that have been grown in soil that has 3 year old traces of pesticides, etc.

That said, raised beds are nice to have anyway.
posted by Good Brain at 11:37 PM on September 12, 2007

You may want to give special attention to beds near the foundation of a house, or near retaining walls or landscaping where treated timbers are used. Termite control compounds, and the chemicals used to pressure treat wood are quite long lived, and so resistant to water solubility that they will leach slowly into adjacent soils for many years.
posted by paulsc at 12:12 AM on September 13, 2007

Definitely get the soil tested. Many pesticides, etc., decompose promptly, but lead is inert and stays in the soil. Improving the soil with biologicals is excellent, so keep it up. You'll find the extension office in the phone book, probably under US Government. One of the best uses of our tax $; they have info on composting, too.

I had lead in my garden soil from leaching from lead-based paint on my old house, and from lead in gasoline hat got into the air, and settled in the ground. I removed the soil and replaced it in the area where I plant vegetables. Lead and most heavy metals are generally not taken up into the plants, but even a tiny amount of dirt on lettuce can introduce lead into your system, so you can grow things that are higher off the ground and easier to clean, like tomatoes, peppers and green beans. Not potatoes.

A friend is still being treated for lead poisoning from remodeling a house with lead paint. It's insidious.
posted by theora55 at 6:44 AM on September 13, 2007

You want to get pesticide residue and trace metals analyses done on your soil, to do it "right". That will be expensive however. Land farming, letting the soil microcosm break the materials down, is probably your best option for the pesticides but will not work well for metals (lead, cadmium, etc...).

For the lab analysis, if you want to go that way, look in your phonebook for environmental constultants and services. You want to make sure that the testing lab is accredited and working to some standard. In the US, the accrediting bodies are NELAC/EPA and A2LA. Make sure that the lab uses either of those two standards. This could be important if you want to sell you house some day.

For the pesticides biodegredation, the limiting factors typically are oxygen---keep the soil well-tilled and encourage earthworms---and moisture. Nutrients are usually less of a problem, but a mulch with clean mushroom compost wouldn't be a bad thing.

If you've got high metals levels, that's much more of a big deal. The only practical option is removal. It doesn't sound to me like that's at all likely in your case, given your description though. However, if you do have a metals problem, I'd want to get an environmental engineering firm involved at that point to get it done right. It's not something you can easily do yourself.
posted by bonehead at 8:25 AM on September 13, 2007

Just to be clear, I don't necessarily think that going for the full PRA is you most cost-effective choice here, but IANY environmental consultant, and I'm not familiar with Californian law. However, if you do decide to engage a consultant, my thoughts above may provide you with some context fro your decisions.
posted by bonehead at 8:28 AM on September 13, 2007

Depends on the chemicals that were used. Some persist for decades; others don't. Some have known collateral toxicities; others just do what they're supposed to. List 'em here and we could be more helpful.
posted by ikkyu2 at 9:05 AM on September 13, 2007

If you really want to know, have the soil tested as bonehead suggests. However it will be expensive, and since you don't know specifically what you are looking for you have to do a huge suite of analysis.

An interesting side note is that many pesticides that have been illegal for decades still show up in soil samples throughout agricultural areas even now. You'd be very surprised how much DDE/DDT is still around. Many communities require grid/statistical sampling of soil on agricultural properties that are being rezoned to residential, and I used to do the sampling. Shocked the crap out of me when I first saw the results. Generally speaking though the residual concentrations were usually determined to be deminimus.

Go with raised beds.
posted by Big_B at 9:19 AM on September 13, 2007

Grow your edible plants in raised beds with new soil. There are a number of plants that sequester toxins from the soil; you wouldn't want to eat them. The practice of using such plants to do this deliberatly is called phytoremediation.
posted by oneirodynia at 9:56 AM on September 13, 2007

Soil testing should cost about $40-50. The local extension service should be able to hook you up. In addition to testing for pesticides, they'll be able to tell you whether your soil is nutrient deficient. I wouldn't worry about the pesticides. After two years of not using them, you should be fine. Lead and heavy metals can concentrate in plants like tomatos and eggplants, so you'll want to know about something like that.
posted by electroboy at 10:10 AM on September 13, 2007

List 'em here and we could be more helpful.

Indeed. If you can tell us anything about the active ingredients and/or the brand names of the products he used, I may be able to be more specific.
posted by bonehead at 10:25 AM on September 13, 2007

You've been eating food grown in similar soils all your life. These soils you know have had at least a two-year break, so why now fear them?
posted by Pollomacho at 1:01 PM on September 13, 2007

Not to hijack the question, but to bonehead and ikkyu2 and fshgrl and others, could you also say more about what you'd test for if you didn't know exactly what was used and how you'd pick which soil to sample (depth, location)? I'm in a similar situation, and it obviously costs a lot more if you take a lot of samples and include a lot of chemicals in the analysis.

To the OP, I would definitely recommend testing for lead. I think you can buy super-cheapo lead test kits at places like Home Depot.
posted by salvia at 11:54 PM on September 13, 2007

salvia: How deep you need to go depends on the root depth of the species you want to plant. Deep roots may mean you need to go down a foot or so, for shallow plants, surface testing may be enough.
posted by bonehead at 7:52 AM on September 14, 2007

Pollomancho: in every case I've seen, the highest pesticide residue levels have always been in residential areas. The scenario described by Anisoptera is typical of high residues. For farmers, on the other hand, pesticide and herbicide application is one of their major business costs and try to spray as little as possible. Farmers are a problem for groundwater and in bioconcentrators (like plants and fish), but their spot levels usually aren't that high.
posted by bonehead at 7:57 AM on September 14, 2007

salvia: eight inches down is considered "tillage depth" for most food crops. Go down to a foot if you plant potatoes (though I don't recommend growing potatoes in home gardens due to their tendency to carry verticillium wilt and the difficulty in digging up all potatoes to control the disease). You don't want to take a surface soil sample unless you're planting a lawn or doing some other specialized test. It is expensive to do anything more than a basic soil test, and very expensive to treat the soil once you've found out what's in it. Unless you're dead set on planting in native* soil for some reason, it's much easier to just build raised beds- you can control soil composition, texture and Ph**, water drainage is much better, and raised beds are easier to work in.

*there aren't really native soils in housing developments.

** proper Ph is key to plants being able to take up nutrients. Very often, correcting Ph means fertilizers are no longer necessary. 6.5 is a good average Ph for gardens.
posted by oneirodynia at 10:38 AM on September 14, 2007

Thanks, bonehead, oneirodynia, and Anisoptera!
posted by salvia at 10:43 PM on September 15, 2007

Anisoptera, if you're still reading this thread, this article is worth checking out. It's pretty general, not specific to whatever are your particular products, but might be worth reading.
posted by salvia at 11:03 PM on September 15, 2007