Potato Growing Claims

[Meadowlark]

@gary350 has mentioned a couple of claims on growing potatoes that he has seen on videos. To wit:

There are 100s of YouTube videos. Commercial growers are the only 1s I trust. I found 2 commercial growers that claim nitrogen at 60 days produces larger crop of new potatoes.

Another grower showed video of them cutting potato plants off at 60 days. They claim if the plants have no tops new potatoes grow larger the last month.

I do not believe either of these claims personally...however I'm running an experiment for fun this year to find out.

In the meantime, I asked one of the largest, longest existing commercial potato growers (also the most I trust) in the USA the two questions and offer their response:

Question 1: Does removing the tops at 60 days increase production?

Response (the short answer):

Cutting the potato tops off at 60 days generally does not increase total production. In most cases it reduces yield, because the plant is still actively photosynthesizing and bulking tubers (sizing them up). If you remove the tops too early, you shorten that bulking period.

What top-killing (cutting vines) is good for:

- Setting the skins for better harvest/handling and storage (you typically then wait about 10–14 days before digging so skins can toughen).
- Stopping growth so tuber size doesn’t get too large (useful for “new potato” size targets).
- Disease management (e.g., if late blight shows up—killing vines can help protect the tubers).

Question 2: Does adding nitrogen at 60 days increase production?

Response (again short answer):

At 60 days after planting, adding nitrogen usually does not increase total potato production unless your plants are truly running short of N. More often, extra N at that point can push vine growth and delay tuber bulking/maturity—especially in your early/determinate varieties.


I propose using this thread for posting results on experiments on answering these questions as well as posting growers experiences. TIA.

 

[oneeye]

@gary350 has mentioned a couple of claims on growing potatoes that he has seen on videos. To wit:



I do not believe either of these claims personally...however I'm running an experiment for fun this year to find out.

In the meantime, I asked one of the largest, longest existing commercial potato growers (also the most I trust) in the USA the two questions and offer their response:

Question 1: Does removing the tops at 60 days increase production?

Response (the short answer):

Cutting the potato tops off at 60 days generally does not increase total production. In most cases it reduces yield, because the plant is still actively photosynthesizing and bulking tubers (sizing them up). If you remove the tops too early, you shorten that bulking period.

What top-killing (cutting vines) is good for:

- Setting the skins for better harvest/handling and storage (you typically then wait about 10–14 days before digging so skins can toughen).
- Stopping growth so tuber size doesn’t get too large (useful for “new potato” size targets).
- Disease management (e.g., if late blight shows up—killing vines can help protect the tubers).

Question 2: Does adding nitrogen at 60 days increase production?

Response (again short answer):

At 60 days after planting, adding nitrogen usually does not increase total potato production unless your plants are truly running short of N. More often, extra N at that point can push vine growth and delay tuber bulking/maturity—especially in your early/determinate varieties.


I propose using this thread for posting results on experiments on answering these questions as well as posting growers experiences. TIA.

Thats good to know.

 

[Meadowlark]

60 days...or 59 days...but who is counting has arrived.

It pained me greatly to cut tops and especially apply synthetic Nitro, but anything for the sake of discovery...

Two potato plants with tops removed at 60 days...

Two potato plants with synthetic Nitrogen applied at 60 days...

Two normal control potato plants...

And here we go...

 

[Meadowlark]

The 90 day point of this experiment has arrived give or take a day or two.

The potatoes are continuing to grow and weather permitting they will remain in the ground another two week...except for the specific three sections of this experiment (2 feet each):

1) potatoes with tops removed at 60 days
2) potatoes with synthetic nitrogen added at 60 days and
3) potatoes grown normally here with zero synthetics added

There are numerous pictures to document the results for each two-foot section and those posts follow.

The summary of results is as shown below:

Item	Tot Number of NP	Weight of NP	Number of Bakers
Tops cut at 60 days	15	11 ounces	0
N added at 60 days	15	34 ounces	0
Normal	30	103 ounces	6

The columns are total number of new potatoes found in each section, the total weight in ounces of those found in each section, and the number of what I call baking potatoes in each section.

The results speak for themselves.

Anyone else have any results to post?

 

[Meadowlark]

The photos for the "tops cut at 60 days section"

 

[Meadowlark]

The photos for the "Synthetic nitrogen added at 60 days"...

 

[Meadowlark]

The photos for the "normal production" section...

 

[Meadowlark]

A third item, potato spacing, also receives a lot of discussion mainly in 6-inch vs 12-inch spacing. I compared four groups of Yukon Gold potatoes with Group 1 and Group 4 at 12-inch spacing and Group 2 and Group 3 at 6-inch spacing.

The results are summarized below:

Item	Tot Number of NP	Weight of NP	Number of Bakers
Group 1 12 inch	10	44 ounces	4
Group 2 6 inch	10	28 ounces	2
Group 3 6 inch	10	32 ounces	3
Group 4 12 inch	11	45 ounces	4

Group 1

Group 2

Group 3

Group 4

 

[Martin Mikulcik]

For the spacing experiment, was it a total of 4 plants? I guess what I'm asking is was the total sq ft per group exactly the same? Because 2 potatoes planted closer would do worse than 2 spaced further, and the plant at the end of the row will do better than one in the middle. A lot of variables to account for

Why do you think nitrogen hurt your yields, because the hypothesis was

At 60 days after planting, adding nitrogen usually does not increase total potato production unless your plants are truly running short of N. More often, extra N at that point can push vine growth and delay tuber bulking/maturity—especially in your early/determinate varieties.

That did not happen. In the photo you provided the one with nitrogen applied had less green vines which indicates they either reached maturity faster or more likely were damaged by the nitrogen.

Maybe the fertilizer exacerbated drought stress?

I'm assuming you tried to normalize seed size but that could have a big effect too

 

[Meadowlark]

Hey thanks for reading and commenting @Martin Mikulcik... Appreciate that.

For the spacing experiment, was it a total of 4 plants?

Yes, and the spacing went like this:

1) plant 1: 12 inches spacing on both sides left and right
2) plant 2: 12 inches spacing on left and 6- inch spacing on right
3) plant 3: 6-inch spacing on left and 12-inch spacing on right
4) plant 4: 12-inch spacing on left and 12-inch spacing on right.

I took a photo with a yardstick in it, but the sun washed it out and by the time I realized it, I had already dug them each up.

Ideally plants 2 and 3 should have had 6-inch spacing on both sides but this is what I had. With 6-inch spacing on both sides I would expect to see more pronounced production degradation vs 12-inch spacing production.

Right or wrong. I felt keeping all four plants together would give the most realistic results.

Why do you think nitrogen hurt your yields, because the hypothesis was

My theory...all my nitrogen is sourced organically (100%) ...which, as you know, breaks down gradually throughout the growing season. This soil tested out in the upper high range of Total Nitrogen ppm as a starting point. Hence, I believe the soil with those plants that synthetic nitrogen was applied to just simply had too much salt from synthetic nitrogen and burned them mostly down as a result.

As an aside, I never side dress or add anything to my plants for the entire growing season. Never.

Many people say nitrogen is nitrogen no matter where it is sourced. I have never ever believed that and in fact completely reject it. Nitrogen sourced organically from composted cow, and Sun Hemp and other covers lasts significantly longer in the soil than any synthetic fertilizer. This result was not surprising at all to me, in fact, I kind of expected it.

...I'm assuming you tried to normalize seed size but that could have a big effect too

Yes, absolutely. My seed size was as close to 2.5 ounces as I can make it...and each of these seeds were very close to that.

 

[Martin Mikulcik]

I'm gonna make an attempt at math.

Your 12in plants had one ft on either side, we'll call that 2ft yielding 44.5 avg

The 6in plant had 6in and 12in so we'll call that 1.5ft yielding 30 avg

1.5 is to 30 as 2 is to 40
Or
2 is to 44.5 as 1.5 is to 33.4

So the difference here is not great on a per acre basis, roughly 10 percent but the sample size is small to say that definitively. And this is somewhat Texas specific

The difference on a potato size difference is very great. You get 50 percent more bakers and if the spacing was reduced further to a real 6in you won't get any large potatoes (at least that was my experience)

I have never burned potatoes from nitrogen, you must do an exceptionally good job with legumes and manure because to me it didn't look in the picture like you gave them all that much. Maybe 15lbs per acre. Maybe you put more than it looked

My argument for nitrogen isn't so much that it's the same or better. It's that it's effective and easy and cheap and renewable and considering just urea and ammonia, safe (well anhydrous can kill you but once it's down). I don't personally apply a whole lot of fertilizer, it wasn't how i was raised. And i like to think my plants are somehow better adapted to poorer soils but that might be coping.

But when i grow field corn in my garden, I'm not getting 200-300 bushel corn. The farmers are. I'm sure you could with the effort you put in. But you gotta admit it's more effort.

You're right about synthetics reacting fast. That's why people like David Hula fertigate so often. And organic matter itself can do wonders to the nutrient and water holding capacity of the soil which would have more effect than some npk would. And when hula was setting records he had nigh 2000$ per acre in inputs.

The record potato yield is over 100000lbs per acre. I can't fathom that. If your rows are spaced 3ft and every ft is a potato, there are 14.5k ft of row per acre, 110oz per plant. But they were probably flavorless.

I appreciate the trial

 

[Meadowlark]

...I have never burned potatoes from nitrogen, you must do an exceptionally good job with legumes and manure because to me it didn't look in the picture like you gave them all that much. Maybe 15lbs per acre. Maybe you put more than it looked

I guess I should of measured but it was less than a handful...not much. I just don't like synthetics in my soil.

This might help with a little more info. Here is the soil test that was taken on that row just prior to potato planting ppm (2026). Yes, I have been getting more efficient at my nitrogen sourcing.

Nutrient	optimal	2020​	2021​	2022​	2023​	2024​	2025​	2026​
pH	5.8-7	6.49​	6.65​	6.51​	6.37​	6.11​	6​	5.8​
Total Nitrogen (N)	32-60	30.2​	34.23​	34.28​	38.9​	32.41​	37.73​	112.54​
Nitrate (NO3-N)		8.1​	9.72​	9.83​	30.1​	10.19​	16.16​	76.04​
Ammonium		5.9​	17.51​	24.45​	8.77​	22.22​	21.57​	36.49​
Phosphorus (P)	8.0-20.	48.2​	75.7​	63.39​	31.6​	68.16​	18.83​	67.27​
Potassium (K)	38-80	116.2​	62.53​	111.27​	115​	50.23​	121.56​	133.37​
Sulfur (S)	7.-22	4.1​	3.47​	7.38​	9.92​	8.22​	6.46​	14.32​
Calcium (Ca)	80-320	300​	499.7​	464.64​	83​	488.3​	253.48​	559.66​
Magnesium (Mg)	27-70	25.4​	24.86​	43.46​	33.7​	57.09​	32.28​	45.79​
Sodium (Na)	.5-30.	6.6​	5.38​	23.17​	13.8​	8.74​	9.91​	27.54​
Iron (Fe)	3.-10.	11.4​	2.7​	14.45​	1.27​	46.84​	1.6​	3.92​
Manganese (Mn)	4.-10.	11​	10.94​	12.56​	4.7​	30.11​	13.98​	23.87​
Zinc (Zn)	.1-.25	0.4​	0.49​	0.52​	0.17​	0.74​	0.43​	0.76​
Copper (Cu)	.06-.3	0.1​	0.15​	0.08​	0.03​	0.1​	0.06​	0.11​
Boron (B)	.2-.6	0.1​	0.11​	0.14​	0.01​	0.06​	0.04​	0.03​

 

[Martin Mikulcik]

Numbers to be proud of.

Do you think boron amendment would do anything?

 

[Meadowlark]

@Martin Mikulcik

A bit off topic...but I'm wondering about your corn comments:

...But when i grow field corn in my garden, I'm not getting 200-300 bushel corn. The farmers are. I'm sure you could with the effort you put in. But you gotta admit it's more effort.

Question: How many ears of corn typically make a bushel?

I would like to convert my yield in ears of corn per five 10 ft rows to bushels per acre. That would be fun.

As far as potatoes goes, my yield on one 80-foot row typically comes in at 250 pounds...on great years 300 pounds and bad years maybe 200 pounds. I usually weigh the buckets loaded with new potatoes to get the estimates... but 250 pounds is pretty much the number. That is with a mix of Red LaSoda (high producers) and others such as Yukon Gold (relatively low producers).

How would that yield compare to your record potato yields?

By the way, I do two potato crops each year...spring and fall...both about the same yields. We love garden potatoes and so do others around here.

 

[Meadowlark]

Numbers to be proud of.

Yes. I usually post my soil test results here under a "number of consecutive years of No N, P, or K' Required" banner that my soil test lab sends me. 7 consecutive years of No N, P, K required. I think possibly members here get tired of seeing it posted annually.

Do you think boron amendment would do anything?

Not on potatoes...but I do amend the soil that I grow brassicas in with Boron. Makes a huge difference.