Unless the herbicide was a soil sterilant, it should be gone by now.

Beyond that, if you know the name of the herbicide, we can be of more help.

If you build raised beds the herbicide that was applied to the soil you build the raised bed on is not going to migrate upward into the soil that raised bed will have.

The use of a soil sterilant in a home garden would be highly unusual! Anything else, you are not likely to encounter any issues and I wouldn't bother to make any kind of barrier or distinction between the two soils. The vast majority of herbicides used by and available to home gardeners break down and degrade rapidly after application and turn into what are essentially harmless elements. After a couple of weeks, the "bad" soil is just plain old ordinary soil. Herbicides (with only a couple of non-homeowner accessible exceptions) just do not persist or remain present in the soil for any length of time.

Although the history of alleged pesticide use would prevent you from having your home garden certified as organic, it will not impact the ability to grow organic produce or any other organic plantings. The plants will be free of any possible contamination.

Shouldn't be an issue. And if you build raised beds, you want to incorporate new soil into native for drainage, and of course things move upward as well so that advice is problematic at best if you believe the (likely incorrect) premise that the unknown herbicide is still in the soil.

Dan

thanks so much, everyone. the herbicide was the dreaded "roundup" (i will NEVER purchase that, or anything else from monsanto, again). so i can safely eat the food grown in new soil atop last year's? fantastic news! i appreciate everyone's help.

Some ways to mitigate potential problems with RoundUp include adding some organic source of Phosphorus (like bone meal), making sure the soil pH is in the acid range (to help with mineralization of the Glyphosate), and making sure there's lots of organic material in the oil to also help with mineralization of the Roundup.

Roundup is inactivated by contact with soil.

Flowerbed,
Roundup is one of the safest non-organic herbicides. I don't know why it's referred to as "dreaded". Perhaps because its relative inocuous nature has led to its overuse and the development of weed resistance?

Roundup (glyphosate) is easily broken down by soil bacteria.

It's my herbicide of choice because it really kills plants, but doesn't hang around afterwards like some others do.

I wouldn't worry about it at all.

"Roundup is inactivated by contact with soil."

If that were true, there would be no need for 'RoundUp Ready' seeds. Monsanto, the maker of RoundUp, has a huge business selling RoundUp Ready (TM) seed for use after treating cropland with RoundUp (Glyphosate). The truth is that RoundUp does persist in the soil, it does get absorbed by plants, and it does reduce plant vigor.

But we have all been through this subject before.

And here I thought RR seeds were for spraying RU after sprouting and growing as the plants were resistant to the spray...

Dan

The issue of residual Glyphosate in soil has been studied for quite some time. I don't have the link to the study, but a school in a midwestern state like Illinois or Indiana had studied the effects of residual Glyphosate in soil. Short answer was decreased plant growth and a lower yield.

That report also described the rate of breakdown (mineralization) and the conditions that were optimal for breakdown of glyphosate.

Yes, Glyphosate, like Phosphorus, binds to soil. But my understanding is that plants will take up Glyphosate just like they take up Phosphorus.

The USEPA Groundwater research people have found evidence of the glyphosate products far downstream for the point of application as well as in soils where this stuff has been applied. None of these are as innocuous as the manufacturer would have you believe. If the USEPA pesticide people actually did the job they are supposed to these products would not be sold.

IMO you are fretting needlessly about this. Even if there is some residual effect (and it would be minor), you're going to use a raised bed so it's really just not an issue.

Build your raised bed, plant your seedlings. You do not need any additional barrier. As a new gardener, I'm confident you will find more troublesome things to worry about soon.

mary's comments above are very much on point. This is NOT something you need to be concerned about. Because this is an organic gardening forum, you will get all sorts of heated replies about the "dangers" of RoundUp but the truth is this is one of the most innocuous of any herbicides, which accounts for its extremely wide use and popularity. Anything can be toxic if applied in sufficient dosage. A highly organic soil - that is, one that has adequate levels of organic matter in it and therefor healthy populations of soil organisms - is extremely effective in reducing the half life and residual effect of glyphosate in the soil. And it is important to understand how the stuff works in the first place - it must be applied to actively growing plant tissue. It does not translocate from the soil to plant roots but rather from the plant tissue through the roots. Planting anything where RU was once used will not affect new plantings, either by killing them off or contaminating the plant.

And yes, Dan is correct - the development of RoundUp Ready seeds was intended to build resistance to the herbicide in specific farm crops so that the herbicide could be used without concern for crop damage.......it has nothing to do with soil persistence.

I'd also not be overly concerned with RoundUp or any glyphosate product leaching significantly into groundwater - the fact that it does bind to soil particles reduces the risk of this significantly. Who knows what obscures studies kimmsr is alluding to but a three year study of agricultural fields demonstrates that less than 1% of applied glyphosate was leached into groundwater or lost as runoff. In one case, a loss of 1.85% (a BIG number....NOT!!) was indicated from a field in which the product was applied at twice the recommended application rate and 99% of that total runoff occurred during a severe rainstorm the day after application. (EPA, 2003)

Here is a link that might be useful: environmental fate of glyphosate