Arboretum News

Growing with John Thull

Meet a research professional who works with the University of Minnesota's Grape Breeding and Enology Project at the Horticultural Research Center.

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Pruning the grape vines in winter. Photo courtesy of John Thull.

Editor’s note: We wanted to introduce you to the team who inspires our organization. Each month, we’ll  highlight a different member of our staff in our “Growing with” series.

By Liz Potasek

The seeds for John Thull’s career were planted when he was a kid growing up on a farm in central Minnesota. He remembers tasting wild grapes growing on pasture fences, trying to grow plants in his sandbox and being shocked to realize that pumpkins were a local crop. 

These days Thull works as a Research Professional at the Horticultural Research Center near the Arboretum’s AppleHouse, and his job involves taking care of the grape vines in the Grape Breeding and Enology Project, as well as growing the pumpkins, squash and gourd featured in the Arborteum’s annual World of Pumpkins display.

His work at the Horticultural Research Center for the past 15 years has provided him a unique opportunity to watch and taste as the University of Minnesota’s development of cold-hardy grapes has revolutionized the wine industry in Minnesota and other cold climates.

What do your job duties involve?

There are so many interesting aspects. Most of my work is dedicated toward managing the 12 acres of research vineyards and supporting the grape breeding efforts of this project, led by Dr. Matthew Clark. I also take part in the wine sensory panel in the early spring. I get to do everything from prepping the soil for planting new vines to tasting the finished wines and just about everything in between.

Pruning vines in the winter is one of my favorite parts of the job. It’s a job that takes time to learn and forces you to imagine which cuts will give the vines the best chance to produce nice fruit with open canopies and also give nice shoot architecture for the next season’s pruning.

We start thousands of new grape seeds in the greenhouse and propagate cuttings from high priority vines every spring. When the soil is ready, we plant out thousands of vines in our nursery and research vineyards. Training and de-suckering the vines keeps us busy throughout much of the summer. Managing weeds and pests throughout the season is a tricky, but necessary part of the job, as well. 

Evaluating flavors and harvesting grapes in the fall are definitely highlights for me. Trellis maintenance is a constant task that always deserves more attention.

I also get to grow the huge variety of pumpkins, squash, and gourds that get sold through the AppleHouse and go on display at the Arboretum every year.

From time to time, I get to help with other projects, like T-budding the apple seedlings onto rootstocks, covering outdoor container plants before freeze-up or assisting graduate students in their research.

Thull helping to assemble the Cucurbita tree, featuring pumpkins, gourds and squash, at the Arboretum in 2020. Photo courtesy of John Thull.

Why are you passionate about your work here at the Arboretum?

Since I was young, I have always loved noticing how plants grew, whether they were in a natural setting or in the garden. Plants like grapevines and pumpkins that have curling tendrils for climbing were especially interesting to me, and the way they produce fruit fascinated me even more. 

Working at the Horticultural Research Center has allowed me to really explore my interest in fruit production. I get to work with thousands and thousands of unique grapevines that all have their own unique fruit flavors and growth habits. Grape growing is a job that never gets boring. I continue to learn new things every season that help refine the timing and technique of my management practices. Being able to work outdoors is especially nice.

I love working on the Grape Breeding and Enology Project for many reasons, but the best part of the job is getting to work side-by-side in the vineyards with my wife, Jenny. She has an amazing ability to taste, describe, and catalog in her mind the flavors of the grapes that we encounter in the fields. You can always find her blasting good tunes and making funny conversation among the rows of vines, yet always keeping everything organized and focused. It’s so nice being with someone who shares my affinity for viticulture (and pumpkins)!

What is your earliest memory of gardening or nature?

Growing up on a dairy farm near Greenwald, Minnesota gave me lots of fond memories of exploring the surrounding nature and growing food in the garden. I remember my dad showing me how wild grape vines would grow on the pasture fence-lines and in the surrounding woods. The first time I tried them, I hoped they would taste like the grapes from the store. Nope! But at least those tendrils were still cool, and the vines were fun to swing on until they broke free from the tree branches above.

I used to try to get plants to grow in my sandbox. This would include field corn from seed and transplanted wild cucumbers and blue Asiatic day flowers. (Little did I know, the latter was invasive.)

My grandmother showed me how to plant strawberries in the garden at the age of five. When I was 7 or 8, I couldn’t believe that pumpkins could be grown in Minnesota as I watched my friend and his grandpa haul some big orange ones into the house before an impending frosty night! That was it for me. I’ve wanted to explore the world of plants ever since.

What inspired your career path?

We used to make wild grape wine on the farm before I went to college in Duluth. I chose a biology path with a focus on plant classes. It was somewhere near the end of my four years when I realized how much I missed making that not-so-refined country wine. 

After college, I thought about studying enology and viticulture at Davis, CA for about a second, but opted instead to do a year-long apprenticeship with a family-run vineyard and winery on the Mosel River in Germany. I loved the whole experience there and learned that growing the Riesling vines was maybe more fun than making the wine, but probably not as much fun as drinking that wine!

When I came back to Minnesota, I knew the University of Minnesota was up to something interesting that involved grape breeding at this quiet outpost of a research center. I thought how nice it would be if I could at least volunteer for a bit with someone who new something about grapes before I did my next stint in another notable wine region. 

I put in a cold-call, got an interview with Peter Hemstad and Sue Riesgraf, and they said we can possibly offer you a 67-day Temp/Casual position. I said, “Great! When can I start?” That was in 2005.

Do you have a home garden?

Jenny and I have a small lot in a woodsy neighborhood that doesn’t get great sun. Jenny’s really the mastermind behind what we have growing around the house, but together we’ve established some beautiful peonies, a couple of fruit trees, some hops and even a grapevine, among other things that are doing alright considering the limited sunlight. We had 4 peach blossoms on a tree last spring. That doesn’t happen all the time.

Photo courtesy of John Thull.

What are the most challenging and most rewarding parts of your work?

In our day-to-day work, the biggest challenge is keeping pace with the growth of the vines as the weather warms up. It quickly turns into a blur of activity in May with many jobs needing attention at once. The biggest reward is seeing all that hard work pay off with a great harvest at the end of the season.

In the long term, the biggest challenge is finding those ‘diamond-in-the-rough’ grapes. It’s a challenge of patience when breeding any kind of perennial plant and that certainly holds true for grapes. It can take several seasons of waiting before we can taste the first grape clusters after the crosses are made. Throughout the years, each vine needs customized care to get it established to this point of fruiting maturity. Broadly speaking, only about one or two vines in 10,000 that get planted in the vineyards have favorable enough traits to make them worthy of naming and releasing to the public. 

Vines typically have 15 years or more of work, research, and evaluation invested in them before they are considered name-worthy. It’s very fun to think about how the next great Minnesota grape variety may already exist in the research vineyards, and it’s just as fun to know that every new season gives another chance to ‘roll the breeding dice.’

As an expert in your field, do you have any tricks, tips or advice that would help our readers?

Growing grapes in the Midwest can be rewarding to backyard enthusiasts and commercial growers alike. It certainly helps to talk to many other experienced growers before you jump into it too deep. The site you choose for growing your vines will have a big impact on their performance. Vines do not like low lying, wet, or excessively fertile land. They tend to produce better fruit flavors on land that is sloped and well drained. When establishing a vineyard, you should expect that it will take about 3 years or more until the vines produce significant fruit. 

Vines are fairly flexible when it comes to pruning rules. If you make a mistake in the early years of training, you can usually fix the vine with pruning in the next season. As vines age in our tough Northern climate, the cordons and trunks tend to accumulate winter injury and fungal diseases that call for a little rejuvenation from time to time. To keep the vines healthy and productive, new canes can be trained in as replacements for these failing portions of the vine. Jenny’s favorite line is, “When in doubt, cut it out!” Fruit trees don’t seem to be quite as forgiving when using that motto.

How does your work impact Arboretum members and visitors in a meaningful way?

The work that we do at the HRC and Arboretum is a continuation of the work performed by previous breeders from Minnesota and all over the world. The climate here is what makes our situation unique. 

The varieties that come through our program can tolerate much colder temperatures then those developed by most other breeding programs. These modern, cold hardy varieties are opening up new wine regions that were previously considered marginal for traditional varieties. Our varieties often have disease-resistance traits that may make them attractive to grow in other existing grape growing regions as well. More disease resistance can mean fewer sprays, which should be healthier for us and the environment. The last 20 years have seen a major uptick in vineyard and winery establishment in Minnesota and other states with similar climatic conditions. It’s an exciting time to watch this budding industry gain prominence in the local food and wine scene as well as in national wine competitions. I can’t wait to see where it goes in the next 20 years. Cheers!

6 comments on “Growing with John Thull

  1. Excellent article about a very knowledgeable and nice man. Congratulations John on 15 years and much success.

  2. mariajette

    That wonderful photo perfectly illustrates the challenges to Minnesota wine grape research! Mr. Thull, if you happen to read these comments, I’d love to know if you’ve stayed in touch with your Riesling-growing mentors in the Mosel region. It seems the German wine business is having to deal with some titanic changes courtesy of climate change, and I worry about the future of Riesling there. As MN gets warmer, are Riesling elements being introduced into MN grape research?

    • John Thull

      Hi Maria,
      Yes, I still have a good connection with our friends in Zeltingen on the Mosel. There has been a growing trend to produce Sauvignon blanc in Germany, possibly due to concerns about the changing climate, but certainly the market there is calling for its production, because enough German consumers are now considering Sauv to be chic. For places like the Mosel, warmer growing seasons can be good for growing Sauvignon blanc, but also for producing dry-style Riesling wines. Typically in cool seasons, Riesling’s high acidity would be balanced with some level of sweetness. A warmer season can lead to lower acid levels in the grapes, which then do not need as much or any residual sweetness to make balanced wines. The final sweetness of the wine is still really up to the winemaker’s liking. I think Riesling will continue to maintain a strong footing in German viticulture, due to its wine-style flexibility.

      We have used Riesling here in Minnesota in our breeding work. Unfortunately, many of the offspring are not hardy enough to make the cut. Even if Minnesota seems to be getting warmer on average, the cold temperature lows are still too extreme for the European varieties. There are a handful of vinifera varieties that have proved to pair well with our cold hardy selections, but the offspring typically need another round of breeding to create something that is truly hardy. With each round of breeding, it’s hard to retain a combination of desirable traits from both parents that outweighs the negative traits. That’s why so few seedlings out of thousands ever get to move forward in the breeding program. It’s a certain amount of luck in the probabilities that we’re hoping for!

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  4. Jim Benkovich

    Hmm, John if you have only one grapevine at home, what variety is it?

  5. John Thull

    Hi Jim,
    It’s Itasca, the white wine variety released a few years ago by the U of M.

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