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Garden Soil #929525

Asked April 24, 2026, 4:47 PM EDT

I have a question on garden soil testing.  Last May we accidentally put weed and feed fertilizer on our vegetable garden.  We do not know the brand as we threw away the bag. We found out we made that mistake when all our tomato plants we planted died.  Anyway, we did not plant anything further last summer.  Do we need to do a soil test and would a soil test even show if the weed part of the weed and feed was still there?  Or would it be safe to plant because its been a year and it would have dissolved? You may call me or email.  

Anoka County Minnesota

Expert Response

Thank you for your question for Extension Master Gardeners. How long an herbicide lasts in soil is dependent on a number of factors. Since it was a weed and feed type, it's probably not as strong as more commercial-type herbicides. This article from Penn State Extension talks about the soil composition (clay or sandy) matters and can affect the pH of the soil. 

Persistence of Herbicides in Soil

A soil test from the U of MN will analyze pH and for a small fee can analyze soluble salts and other trace elements. I would suggest you do this soil test since herbicides can linger for months, depending on the herbicide used. Here is information on obtaining a soil test from the U of MN:

Soil testing for lawns and gardens | UMN Extension

An Ask Extension Expert Replied April 26, 2026, 10:53 AM EDT

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