Plant science for plant people.

The bacteria on a kale leaf can tell you where it grew. Near Washington, DC, a computer program guessed which of seven urban farms and gardens a sample came from just by reading its microbes.

Researchers sequenced the microbes on 92 leaf samples and in the soil hugging the roots at each site. Every farm carried its own mix. The strongest sorting forces were things growers choose: where the irrigation water came from, and how acidic and moist the beds were. Some leafy greens were also rich in Lactobacillaceae, a bacterial family linked to fending off plant diseases. A gardener's habits end up living on the salad.

If a plot's tiny soil organisms are that local, can you move them? A wheat study says yes, in small doses. Blending just 1% soil from an organic field into conventional soil protected wheat from three fungal pathogens, Rhizoctonia, Fusarium and Sclerotium. That 1% blend matched pure organic soil on most measures, including growth. Another review this week found a bacterium called Pantoea riding inside wheat seeds from one generation to the next, so plants pass their helpers along too.

The microbes on your kale record how you garden. A spoonful of healthy soil is enough to hand that record to someone else's beds.