In this episode of Vineyard Underground, Fritz welcomes soil scientist Dr. Jaclyn Fiola for an in-depth discussion on one of viticulture’s most misunderstood nutrients — potassium. Drawing from her recent research and extensive fieldwork across the Mid-Atlantic region, Jaclyn breaks down how potassium behaves differently from other macronutrients, where it originates in the soil, and what makes its availability so complex for grape growers.

Fritz and Jaclyn explore why vineyards in the Eastern U.S. often see discrepancies between soil and tissue potassium levels and how that can impact grape quality, vine health, and ultimately wine pH. They dive into the implications of both potassium deficiency and excess, emphasizing how water availability and soil mineralogy play pivotal roles in potassium uptake. Growers will also learn why standard soil tests may not give the full picture — and why plant tissue testing, particularly whole-leaf sampling at veraison, is often more reliable.

Jaclyn shares the results of her groundbreaking study, highlighting best practices for sampling, how to interpret potassium levels accurately, and actionable steps for managing young versus mature vines. Whether you're planting a new vineyard or managing high potassium levels in an existing one, this episode equips you with the tools to make more informed nutrient management decisions.

In this episode, you will hear:

• Potassium largely comes from soil parent material, not organic matter, making it harder to assess with traditional testing.

• Moisture-rich soils increase potassium availability, especially in non-irrigated Eastern vineyards.

• Whole-leaf tissue testing at veraison gives the most accurate indication of potassium status in grapevines.

• Too much potassium can raise wine pH, affecting mouthfeel, color, and shelf life.

• Before applying potassium fertilizers, understand your soil minerals and use targeted tissue testing to avoid overcorrection.

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Resources:

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If you are starting a vineyard or thinking about starting a vineyard, apply to be on the podcast for Fritz’s help planning your vineyard - https://www.vineyardundergroundpodcast.com/contact/

Today’s Guest:

Dr. Jaclyn Fiola is a soil scientist who specializes in vineyard soils and soil science pedagogy. She works as an Assistant Professor of Soil and Environmental Science at Delaware Valley University.

Connect with Jaclyn, follow her, and view her research.

Episode Sponsor:

Today’s episode was brought to you by Vigneron Toy Store and the Inside Winemaking podcast.

Thank you to Vigneron Toy Store for sponsoring today’s episode. Vigneron Toy Store specializes in Harvesters, Sprayers, Frost Mitigation Equipment, Canopy Management Trimmers, and more. As grape growers themselves, they can expertly help you determine the best equipment for your specific vineyard needs. And, as a special offer for our podcast listeners, you can save 5% off in-stock machines by entering the promo code Underground on the contact form at vignerontoystore.com.

Thank you to the Inside Winemaking podcast for sponsoring today’s episode. To learn more about the art & science of winemaking with Jim Duane, visit www.insidewinemaking.com/ and listen to the Inside Winemaking podcast on your favorite podcast app with new episodes releasing every other Tuesday.

Episode Credits

If you like this podcast and are thinking of creating your own, consider talking to my producer, Emerald City Productions. They helped me grow and produce the podcast you are listening to right now. Find out more at https://emeraldcitypro.com. Let them know we sent you.