Does Cutting Seed Potatoes Increase Yield? What Is The Effect Of Cutting Potato Tubers On Yield? That’s What This Post Is About. The Answer Surprises Many Gardeners.
Potatoes (Solanum tuberosum) are one of the most discussed garden and allotment veg crops grown in the UK. From how to grow them and what sort to grow and about potato blight to how to chit potatoes and whether to cut seed potatoes into smaller pieces. Cutting seed tubers is what this post is about but there are links to other potato growing questions dotted throughout the article.
One of the most common question I get asked about this topic is “can you cut seed potatoes in half“. It’s simple question and deserves a simple answer. The problem being it isn’t quite that simple to answer!
Potatoes are from the same family as tomatoes and deadly nightshade. Which always makes me wonder why some species in this family are deadly to eat and others have become staple food crops. Even more surprising in a sense is that the fruit of the tomato is excellent to eat but the fruit of the potato is toxic. Because of course the seed of the potato, which is on those toxic fruit, isn’t what we plant as “seed” potatoes. They are actually tubers.
And fresh seed potatoes, the virus free ones grown in areas where there are few virus spreading aphid, are quite pricey. Places like the highlands of Scotland, which is why a lot of seed potatoes are Scottish seed. Some even come from windswept Scottish islands. And there are of course Scottish varieties such as Arran Pilot and the various Pentland varieties.
I digress. Back to the main question?
Does it makes sense to cut them into pieces before planting them?
First lets look at the purpose of the tuber.
Why Do Potatoes Produce Tubers?
Tubers are the plants food store to allow it to survive from season to season. During there greeting season the plant grows stems and leaves to begin with and then puts all its energy into producing tubers. The reason for this is that the plant is not frost hardy and wil die during winter. The tuber then produces a clone of the original plant as soon as conditions permit, usually in the spring of the following year.
Being clones each of the following plants has the same genetic material as the parent plant (except for possible “mistakes” that occur during the process). The plant often produces a few seeds on the “potato apples” it produces. These are genetically variable as they have been pollinated by pollen from another potato plant. That gives the plant a second way in which it can survive.
But here’s the important thing about tubers. They are the new plants food source until it is big enough to “fend for itself”. And the more food the better chance it has and they quicker it can get to the size where it can grow new tubers.
So the bigger the tuber the better the next crop is likely to be. If we cut the tuber into small pieces the food store is diminished and it reaches optimum size later. That means less time to grow more tubers.
Can Seed Potatoes Be Cut & Still Produce A Viable Crop?
Potatoes tend to have several eyes in each tuber, that will produce the stems and roots of the subsequent crop. Usually there are only a handful of them, but every one of them can produce a viable plant that can crop. Some, like the progenitor of the Jersey Royal, had 15 eyes and produced 15 plants when carefully sliced and grown.
The problem with cutting the tuber is that it exposes a raw face which can pick up soil borne diseases. And if that happens the tuber can quickly rot. So the advice is often given to “heal” the wound by applying wood ash to dry the cut surface, or allowing it to air dry. Both seem to work, though I’ve never conducted trials to see how effective this is or if one is better than the other.
The reason that gardeners tend to cut tubers is to reduce cost. A bag of seed potato tubers can go 2-4 times further if cut into halves or quarters. This financial pressure means some societies and cultures tend to cut tubers more than others. More on that in a while.
The question is, does it make sense to go for saving a bit on seed costs make this an economic proposition? Or will the yield be reduced to such as extent that the overall yield drops. And its overall yield that matters in my view because it is far easier to feed, water and weed a small potato patch than spread them out over 2-4 times the space and have a lot of extra work.
I’m always very keen to grow as much as is practicable on a plot of land and not have ea lot of extra work unless it is necessary. It’s not me being lazy. It’s me being efficient and cost conscious.
What Does Research Say About
This is where the problems start. Often when I check the research databases I find either a lot of research on a topic or none at all.
In this case there is research, but I’m not sure it is worth the effort of reading it. It’s not that it is poor research. Its very well conducted research and is fill of useful information .. sort of.
The problem is due to those cultural issues I mentioned earlier.
In poorer countries there is strong financial pressures to reduce seed potato cost so a great tendency to cut tubers into as many pieces as they can. In Western Europe, with many large affluent potato growers, seed potatoes are rarely cut into smaller pieces. The costs of doing it are just too high even if they yield well.
Of course that wasn’t always the case. Historically, and on smaller farms, there was a tendency to cut the tubers. Indeed, in some societies they planted potato peel and ate most of the potato. Tomes were often that hard.
Much of the current research on cutting tubers in to smaller pieces is from Africa where financial pressures make it the norm.
In Senegal the potato is an important vegetable crop. Seed tubers are cut and research by Pape Diop, Elhadji Serigne Sylla, Mamadou Diatte and Babacar Labou indicate that …
“Our results indicated a clear advantage to plant whole and pre-germinated (chitted) seed potatoes with the aim of producing healthier daughter tubers and increasing yields.”
In Uganda Kunihira Patrick and Bruce Robin Nyamweha conducted research into the same topic and reported as follows.
“Slicing of tubers contributes to a big decline in the potato yield as evidenced by poor harvest of plants planted by sliced tubers. The growth of Irish potato too is affected by tuber slicing indicated by low germination and short heights of plants. This poor crop performance of plants from sliced tubers, could mistaken for poor variety performance. The study was conducted on Victoria variety potato so there is need to confirm the results with other potato varieties.”
We should be careful in interpreting these results. They are valid for where the research was carried out. But the same research carried out in the UK might yield different results. Though I personally doubt they would be that dissimilar!
There is however some information about UK trials that is worth considering.
In Effects of cutting seed tubers on number of stems and tubers and tuber yields of several potato varieties, E J Allen writes as follows.
Six experiments are reported which examined the effects of various seed cutting treatments on numbers of tubers and tuber yields of several maincrop potato varieties. Using conventional potato ridges, the cutting of seed tubers into 12 mm cubes or the use of potato peel reduced early growth and yields compared with whole tubers in some experiments but in two others had little effect on tuber yields. In Majestic, seed cutting produced large increases in number of stems and tubers and increases in yields of small sized tubers. In Pentland Crown and King Edward, the effects of seed cutting were small. In King Edward no differences in growth and yield were found between individual eyes and in this variety and Pentland Crown, 56g whole tubers produced similar yields to halves of 112 g seed tubers planted at the same seed rate.
The implications of cutting for use in commercial production are discussed in the publication so if you are interested it is worth reading more of it.
More Thoughts on Cutting Tubers
As explained earlier the bigger the tuber the better. And the African studies seem to back this up. However, in Africa growing conditions can often be sub-optimal. If we can provide excellent conditions we might overcome that to a greater or lesser extent.
Conclusions: Does Cutting Seed Potatoes Increase Yield?
In Africa the answer is clearly NO. It actually reduces yield.
In the UK, peelings and small tuber sections decreased yield in some cases but in others had little effect on tuber yields. So it perhaps depends on the variety being grown.
Based on this it might be OK to cut tubers in some cases in garden or allotment situations. But I wouldn’t advise it on commercial crops due to the high cost of labour to cut them.
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