farmblog towards actually sustainable farming in Ahualoa

I did the harvest today, and here are the results, in terms of grams of potato per plant:

Yukon Gold	144
Dark Red Norland	113
Kennebec	283
Red Gold	244
Kattahdin	75
La Ratte	13
Papa Cacho	27

This is pretty awful.  For comparison, just planting random store-bought yellow potatoes gives around 250 g/plant, while better-performing varieties (Island Sunshine and Yukon Gem) on my farm have produced 400-800 g on average or even well over 1 kg in lucky cases.

The one promising bit here is the Kennebec:

Kennebec did the best in this trial, basically due to surviving a few days longer before dying back.  I might try this variety again, starting from fresh imported seed potato, on newer garden beds.

All the other varieties died back before producing any substantial potatoes.  As I’m not a botanist with a laboratory, I have no way to determine what causes the die-back – presumably some fungal blight, but which one? From looking at online images, I would say that the die-back looks somewhat like late blight, but not really at all like early blight.  There are also dozens of other potential fungal and viral potato issues, and no way to know which I’m encountering, which is frustrating.

Here’s the chronology on the potato trial:

2020.07.20: planting day

2020.08.16 (day 16): all the potatoes have emerged and are growing nicely, except for the smallest varieties (Laratte and Papa Cacho), which are barely emerged and tiny plants.

2020.09.03 (day 38): The plants have been mounded (hilled) with regular garden soil.  Nearly all plants are showing early signs of some kind of blight, starting with brown spots on the leaves: 

One of the yukon golds is already completely blighted, down to bare stems:

2020.09.12 (day 47): Almost all the plants are completely blighted to the point of losing almost all their leaves:

The only exception is three plants in the middle of the bed, I believe they are the Kennebec, which appears almost unaffected by any blight:

This is a good result.  It is difficult to find details on Kennebec, but one reference did suggest it has “good field resistance to late blight”.  The little “Papa Cacho” variety at the end of the bed also appears to be relatively unblighted, but since the plants are so small, it’s not as promising for yield.

Today I examined the seed potato that we got for the trial. 7 varieties. Many were starting to decay.  No doubt proper potato storage would involve a temperature or humidity controlled environment, but we don’t have such a thing, so a few were lost.  Nearly all were at an advanced staged of growing eyes, many also had roots.

I planted them in one of our typical well-drained raised garden beds, 3 x 21 feet, with enough room for 38 plants.  All our beds are similar in regards to soil makeup: the base is Hamakua clay soil, highly improved with organic matter over the years (mostly compost), and a few percent biochar.  These beds have grown a long series of crop rotations, including brassicas and alliums and legumes, but almost never other solanaceous crops.  The ground was damp due to the recent hurricane dropping around 4 inches of rain yesterday.  I made little holes and set in the potatoes, then covered.

Total planting was 14 yukon gold, 3 dark red norland, 3 kennebec, 12 red gold, 1 kattahdin, 2 laratte, 3 papa cacho.  We’ll see how they do!

Besides variety, one variable I added to this test is that of the 14 Yukon Gold, 8 of them got fertilizer (organic biocrumbles 6-6-5) in their planting holes.  I have never used fertilizer with potatoes before, but perhaps we’ll see a difference in these 8 vs. the other 6.  Then again, if my theory is correct regarding dieback as the single largest factor in yield, perhaps it won’t make much difference.  As noted in the last post, from what info I could find, none of these varieties are strongly resistant to the soil fungal issues which appear to be the limit here.  For example, this trial has Yukon Gold, instead of the Yukon Gem which has much better blight resistance.

We’ve always grown potatoes occasionally, since I was growing up here, but recently I became more interested in really knowing potatoes and hopefully increasing production.  To this end, I started a spreadsheet to track planting and harvests, and ordered some seed potatoes for variety trials.

Background: We used to just use organic potatoes from the health food store. Some would start to sprout before we got around to eating them, and they got planted in the garden. The yield was never very good, but at least it made a few small potatoes per plant, so it was worthwhile.  We had no idea what we were doing, but it was OK.

In 2019, I ordered sample packs from Wood Prarie Family Farm (“Certified Organic Maine Certified Seed Potatoes”).  It included four varieties – Fingerling, All blue, Caribe, Yukon.  The yield was (what I now know is) dismal: under 300 g/plant, except for one set of All Blue which almost managed 600 g/plant.

I continued to plant our rotating set of unknown varieties as well (saved over the years from those store potatoes).  These “misc yellow” and “misc red” varieties also produced poorly, the yellows never exceeded 300 g/plant and the reds were lucky to reach 300-600 g/plant.

I eventually did a lot of reading on potatoes online, and a textbook on potatoes from the library.  I learned a lot about potato history, genetics, and diseases.  I learned that by re-planting our own potatoes year after year, we were probably accumulating an increasing number of potato diseases.  The only way around that is to order seed potatoes from a very cold place (like Maine) where the winter kills most pathogens.

From observation, the overwhelming factor that determines yield, in our gardens, is how long the plants live before dying back (from unknown blights or diseases).  Nearly everything we plant dies back prematurely, when the potatoes are still small, and that completely explains the low yields.  It doesn’t appear to be insects, or rot, or anything visible.  Just plants dying back too soon.

So, in 2020 we ordered a more serious amount of Maine potatoes.  We are at 2500′ in Ahualoa, 80-200 inches of rain/year, so we knew we need something that tolerated wet conditions. We chose these cultivars, which Wood Prarie described like this:

• Red Norland. Yield medium-heavy, Late Blight Tolerance Medium.
• Yukon Gem. Yield medium-heavy, Late Blight Tolerance Medium-high.
• Island Sunshine. Yield medium, Late Blight Tolerance Very High.

As the spreadsheet shows, the yield has corresponded loosely with the “blight tolerance”.  Red Norlands did the worst (264 g/plant), Yukon Gem significantly better (692 g/plant).  The Island Sunshine did something fascinating!  I planted a long 21-foot bed of 30 plants.  Most of the bed died back early, and averaged a poor 350 g/plant.  But 4 plants – all next to each other, in the middle of the bed – somehow escaped the dieback.  They continued to grow huge, and produced an astonishing 1294 g/plant.

My theory, at this point, is that our garden soils, from years of growing a large variety of random vegetables including potatoes, have accumulated a load of potato pathogens, and that somehow those four plants (in a relatively newly expanded area of the garden) got lucky and grew in a patch of soil that had none of the (fungal? blight?) pathogen.

I’d love to believe that it might be genetic, that those 4 Island Sunshine plants might have some genetic variation that caused them to overcome whatever issue our soil has.  But, what I’ve read about potato genetics says that’s highly unlikely.  Of course, I’ll be re-planting just the potatoes from those four plants, but chances are, they will be limited by the soil I plant them in, not their genes.

Today, UH-CTAHR did a small distribution of seed potatoes for citizen science experimentation.  I am delighted they are doing this.  I picked up my seed potatoes today.  These are the varieties I got, along with what I could find on their supposed disease resistance:

• Yukon Gold – “medium tolerance of late blight”
• Papa Cacho -“robust plants with obvious resistance to late blight”
• Red Gold – “resistant to potato leafroll virus and potato virus Y and moderately resistant to common scab, but is susceptible to potato virus a and potato virus s.”
• La Ratte – “resistant to scab and viruses”, “low yield”
• Dark Red Norland – “resistant to scab, growth cracks, hollow heart, early blight, and rhizoctonia (black scurf)”, “medium tolerance of late blight”
• Katahdin – “consistent performance”, “moderate resistance to scab”
• Kennebec – “good field resistance to late blight”

Of these, I’ve already grown the Yukon Gold and Red Norland, and seen very low yields.  The Kennebec and Red Gold might do OK? It’s hard to guess; we’ll find out.  The problem with doing a trial like this, though, is that there are only 3 spuds in my Kennebec bag, with cutting, enough for probably 5-6 plants.  What if those few plants get lucky or unlucky with a particular part of a garden bed, like the Island Sunshines seemed to?  In that case, any variety-specific traits are overwhelmed by the variation in the soil issues, and we won’t know if the variety is good or not.