"Identifying Ideal Seed Size To Optimize Yield, Gross Return" in green serif font
"Ideal sizes vary by variety" in green serif font
Pile of $100 bills
There has been a fair amount of discussion and research over the years about the ideal seed size for seed potatoes. The discussion has also included whole vs. cut seed and the advantages/disadvantages of each.

As research methods improve and become even more precise, the opportunities to find answers to what the ideal seed size is for planting and whether you should use cut or whole seed are becoming even more clear.

Well, for the most part. In a presentation at last summer’s Potato Association of America annual meeting in Missoula, MT, Hailey Hampton, a master’s research student at the University of Idaho offered some of the latest research on ideal seed size and type, with her research focused on specific potato varieties. Hampton also tied into her research the costs associated with using different seed sizes and whole vs. cut seed. That’s what we mean when we say research is getting more precise.

Hampton, who is conducting her research with University of Idaho potato researcher Rhett Spear, focused her studies on the Clearwater Russet. But the research also includes studies comparing Clearwater Russet with two additional varieties: Russet Burbank and Ranger Russet.

From Hampton’s abstract: “Clearwater Russet, a variety released from the Pacific Northwest Variety Development Program in 2008 and accepted by McDonald’s in 2016, has substantially increased in acreage in the Pacific Northwest due to desireable processing characteristics. Potato seed size plays an important role in emergence and plant establishment. Moreover, seed size may affect economic returns by altering seed costs.

Aberdeen, Idaho Site Of The Study
“Research was initiated in 2021 in Aberdeen, ID, to identify ideal seed sizes and to investigate differences resulting from planting cut versus whole seed tubers for Clearwater Russet that maximize financial returns through improved yields and cost reduction.”

Research from that first year did yield some specific results—which Hampton presented at the PAA meeting—and another year (2022) of research, which concluded before we went to press with this issue, offered even more insight, at least preliminarily.

First, we’ll present research findings from 2021 and then update those results with 2022 data later in this article.

Again, from the abstract, “Initial data indicate trends toward varieties reacting differently when seed sizes of 1 to 3.5 ounces are planted. Data for Clearwater Russet tends to indicate a seed size of 2.5 ounces produces better yields and cost-adjusted gross returns compared to larger and smaller seed sizes. Data also indicates a trend toward increased yields and cost-adjust gross returns for cut seed pieces versus whole seed pieces.”

It was pointed out, though, “This data is derived from a single year and therefore cannot be completely conclusive, although some patterns appear to be emerging.”

Flatbed pickup carrying sacks of potatoes
Part of the 2021 potato crop headed to the lab to be studied for yield, tuber size and other study parameters.
University of Idaho Master’s Research student Hailey Hampton
University of Idaho Master’s Research student Hailey Hampton.
Two Trials
Hampton pointed out that the 2021 research trials actually included two trials. She said, “The first one involved Clearwater Russet and it was a cut vs. whole seed and varying seed sizes-trial. And in the second one we took three different varieties and did strictly a cut seed with varying seed sizes trial.”

She explained why Clearwater Russet is so appealing to processors. “Some of the prominent Clearwater Russet characteristics are that it’s resistant to sugar ends, growth cracks, black spot bruise, tuber late blight and PVX as well as also being moderately resistant to verticillium wilt, common scab, PVY and hollow heart and it also has a cold sweetening resistance,” she said.

Focusing on seed potato size, Hampton explained, “Seed size can affect the average number of eyes per seed piece which can have an impact on your stand density as you get more eyes you tend to have more dense stand, more stems per piece and that, in turn, can impact your yield. There is also the economic impact to consider as whole seed is more expensive than cut seed.”

Hampton said that after her presentation in Missoula she got a comment that she said probably needs to be figured into her research. She said, “During my presentation, I actually received a very interesting point from a grower who asked a question. That being that the cost of farmers cutting their own seed could be factored into the cost of purchase, which I hadn’t considered. This additional cost could bring the initial financial advantage to buying seed for cutting to about the same as purchasing whole seed tubers.”

She added that she was in the process of reaching out to local growers in an effort to find a cost estimate which she will factor into a financial analysis.

Student next to big bin of potatoes
Harvesting the 2021 research potato crop
Whole vs. Cut Seed
She continued, “There are some differences between planting whole versus cut seed as well. When planting whole seed you may expect more tubers per plant but it will probably produce some smaller tubers. The seed itself is more expensive and you may need to have a planter that is capable of effectively planting whole seed tuber. You may see slower emergence but there may be less seed disease potential, whereas for cut seed it may produce more large tubers but you will see fewer tubers per plant and the seed itself is cheaper. You might see faster emergence but it may have a higher seed disease potential.”

With each variety five seed sizes were studied: 1, 1.5, 2, 2.5 and 3 oz. As you can see, the sizes were divided into half-ounce increments.

Seed size conclusions from the 2021 trials showed:

  • Total Yield: 2.0-2.5 oz. for all varieties
  • Gross Return: 2.0-2.5 oz. for all varieties
  • Tubers Per Plant: 3.0 oz. for Clearwater Russet
  • Tubers Per Plant: 2.0-2.5 oz. for Ranger Russet
  • Tubers Greater Than 10 oz.: 2.0 oz. for Russet Burbank
When it comes to total yield, the 2021 results showed for Clearwater.

Russet, a seed size of 2.5 ounces produced the highest yield with 3 oz. seed coming in a close second. With the Ranger Russet, 2.5 oz. seed also produced the highest yield with 2 oz. seed a close second. As for the Russet Burbank, 2.0 oz. seed produced the highest yield, followed closely by 1.5 and 2.5 oz. seed.

As for the percentage of tubers greater than 10 oz., research indicated that for Clearwater Russet that seed weighing 1, 2.5 and 3 oz. produced about the same percentage. With Ranger Russet, 2 oz. seed produced the highest yield of 10 oz. plus tubers as it did with Russet Burbank. The 2.5 oz. seed potatoes came in a close second in Russet Burbank while 3.5 oz. seed was second in Ranger Russet.

Rows of growing potato crop
The potato crop during the 2021 growing season.
Updated Results – 2022
Again, it was stressed that the 2022 study results were not quite complete by the time we went to press so any findings were preliminary. The results were fairly different from 2021 compared to 2022, possibly due to the cool spring temperatures. For example, larger seed potatoes showed the highest yields in 2022 whereas in 2021 in was the 2.0-2.5 oz. That was true almost across the board for all varieties. More specifically, researchers found in 2022 that the highest yielding seed sizes were 2.5 oz for Clearwater Russet, 2.5 oz. for Ranger Russet and 3.5 oz. for Russet Burbank. Hampton said they were still analyzing the data.
Dirt rows after crop harvesting
University of Idaho researchers are studying the ideal potato seed size on three different varieties and which size might give the best return in yield.