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Using Vegetable Variety Trials to Make Better Seed Decisions

Author: Cindy Tong. Have you ordered all the seed or cuttings for the upcoming season yet? Are you inundated with seed and plant catalogs, and can’t decide what you want to plant this year? How does one decide what to buy? You could talk to other growers, seed company representatives, or look for variety trial information.

Midwest Vegetable Variety Trial

Purdue University compiles vegetable variety trial information from many states, including Indiana, Maine, Michigan, Massachusetts, New Hampshire, Ontario (yep – the Canadian province), and Wisconsin. You can find the information online here.

These include trials for heritage beans, pickling cucumbers, eggplant grown in high tunnels, melons, bell and mole peppers, pumpkins, summer squash, sweet corn, tomatoes, watermelon, and more.

Sometimes a variety trial is interwoven into an experiment testing some other practice, like transplant date or spacing. 

For example, among the 2018 studies in the Purdue University compilation is a 2018 trial done by Marissa Shuh and Will Jaquinde of Michigan State University testing six different indeterminate tomato varieties started in pots or soil blocks, and then transplanted into a hoophouse or in the field.
The six varieties that were tested were Caimen, Damsel, Frederik, Green Zebra, Moskvich, and Valencia. The traits that were measured were fruit yield, amount of cracked fruit, and days to harvest.

The researchers found that yield was not affected by the way the transplants were grown (in pots or soil blocks), and that what mattered most was variety. Days to harvest in the hoophouse were about 112 days, and about 99 days in the field. Of the six varieties, the greatest marketable yields were measured for Caiman and Fredrik, both of which are hybrids.

This was a relatively small trial, with only 3 plants of each variety in a study block grown together in two beds in either the hoophouse or field plot, and may be considered a type of “screening trial”. Screening trials are good for comparing traits like color or germination rate on a particular area of a farm.

Screening Trials vs. Replicated Trials

Master Gardeners across Minnesota do similar screening trials, and you can find their results here. The problem in interpreting the Master Gardener results is that you don’t know the conditions under which the plants were grown, how many plants of each variety were trialed, whether a variety that had a high yield produced all of its fruit early and then died of disease or produced fruit slowly but steadily over the season.

Results of screening trials are a good place to start if you’re looking for varieties to try on your own farm. But for traits like yield and pest resistance, variety trials should ideally be set up to test differences among varieties, minimizing differences in environmental conditions, such as soil type, drainage, and exposure to nutrients, water, and sunlight.

To assess the consistency of test results, we University workers like to replicate trials in multiple plots at one site, and then further replicate the trial in multiple locations (like in Saint Paul AND Waseca AND Grand Rapids), exposing whatever we’re trialing to different environmental conditions. Just to be sure, we also like to further replicate the trials over multiple years because one year it might “snowmageddon” in April and have an average high of 75 °F in August, and in another year it might not snow at all in April, and be 95 °F for the whole of August.  Plus, prevailing winds might differ in the two years, bringing different insect and disease pests.

Case study: Cauliflower trial

For example, for our Variety x Transplant Date cauliflower experiments last year, we decided to test the varieties Snow Crown and Freedom. Snow Crown is listed in seed catalogs as maturing 50 days after transplanting. Freedom is supposed to mature 65-70 days from transplanting.

We chose Snow Crown as one of the varieties to test in 2018 because we grew it at the Southern Research and Outreach Center in Waseca and on the University of Minnesota Saint Paul campus in 2017, and gotten harvestable heads in Waseca by 63 days after transplanting, and in Saint Paul about a month later.

In 2018, we were able to harvest heads of Freedom cauliflower in early August from a farm in Long Prairie, and in late August in Waseca and Saint Paul. The transplants had been planted in late May to mid-June, so produced harvestable heads by 70-80 days after transplanting. A few Snow Crown plants started forming heads in September, about 100 days after transplanting, but most plants never formed heads.  We haven’t yet figured out why Snow Crown produced heads in 2017 but not in 2018. However, we did decide not to use Snow Crown in our 2019 experiment due to its unreliability in our field sites over the previous two years.

Doing replicated trials gives us some confidence that Variety A will most likely produce more than Variety B in most locations. We hedge our recommendations because something that can be true 95% of the time could still not apply 5% of the time, and not in all locations.

If you want to do variety trials on your own farm, the Organic Seed Alliance provides a publication on how to do this.

Author: Cindy Tong, Professor and Extension Postharvest Horticulturist

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