How hemp stalks ret in the field

After mowing, hemp stalks lie in the field for a few weeks while fungi and then bacteria feed on the pectin that glues the bast fiber bundles to the woody core. Dew, rain and warmth speed them up, and turning the row lets both sides ret evenly. Stop too early and fiber stays stuck to the hurd; leave it too long and the microbes start weakening the fiber itself.

Controls

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Animation speed

Average air temperature

Wet days per week (rain or heavy dew)

Turn the windrow

Step through it

Stalks in the windrowFreshly mowed stalks lie on the stubble. The bast fiber sits in the outer skin, glued to the woody core by pectin.
Fungi arrive firstMolds settle on the stalks within days and push in through cracks and pores, releasing enzymes that break down pectin. Without moisture they barely work.
Warmth speeds it upMicrobes work faster when it is warm and damp. At 22 °C with frequent dew, the stalks gray out well before day 21.
Turning the rowThe underside touches damp soil and rets faster than the sun dried top. One or two passes with a rake flip the row so both sides finish together.
Knowing when to stopWarm, wet weeks can push the stalks past ready. Bacteria then start attacking the fiber walls, and strength drops.

What the microbes are doing

Microscopy studies of field retting found fungi colonizing hemp stems first, followed by bacteria that showed up after about a week and later took over. Both groups make enzymes, mainly pectinases, that dissolve the pectin between fiber bundles and between the bast and the woody core. Over retting damages the fiber cell walls themselves.

Extension guidance puts field retting at roughly 2 to 4 weeks, with the windrow turned once or twice. Researchers report a wider range, from about two weeks to ten, because weather controls the pace: a hot, dry spell can nearly stop retting by drying the stalks.

Try it: set wet days to 0 and watch the days to retted jump, even when it is warm. Then set temperature to 25 °C and wet days to 7: the row is past ready long before day 21 and the quality flag turns to over retted.

The model here (simplified)

This is a teaching model, not a forecast. Daily progress is degree days above 4 °C, multiplied by a moisture factor that rises from 0.15 with no wet days to 1.0 with four or more wet days per week, plus a 10 percent bonus for turning. The row is called retted at 200 moisture weighted degree days, a value chosen so typical conditions land in the 2 to 4 week range. Real growers judge readiness by color and by how easily the fiber peels from the core.

Sources

Elucidating field retting mechanisms of hemp fibres for biocompositesBioResources (peer reviewed, NC State University)
Harvesting Industrial Hemp: General Considerations (MX79)University of Missouri Extension
Hemp: From Field to Fiber, A ReviewTextiles (MDPI, open access)

How to cite this model

Avid Solutions International. (2026, November 11). How hemp stalks ret in the field [Interactive 3D model]. Avid Field Lab. https://avidsolutionsintl.com/explore/hemp-field-retting

Last updated November 11, 2026

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