Does Cutting Up Seed Potatoes Improve Yields?

No respectable vegetable garden is complete without a crop of potatoes. With so many delicious varieties available, and almost as many delicious ways to cook them (Danish caramelised potatoes anyone?), you'll want to maximise your spud yield as much as possible.

If you have limited growing space, it's important to make the most out of every square inch of soil. So if you can increase the number and weight of potatoes harvested from each plant, you'll get even more tubers to last you well into the winter and through to the hungry gap. 

One method of increasing yield I've been looking into is cutting up seed potatoes before planting, and there is a lot of discussion out there on the pros and cons. 

Paul from the Plan Your Patch blog carried out his own experiment by planting whole, halved and quartered seed potatoes and then weighing the harvests. He found that halving potaoes generally produced a larger yield than leaving them whole, but quartering them resulted in a lower yield. However, Paul also found that the cut potatoes were more likely to rot in the ground if planted too soon, but the increased total yield from the larger number of plants produced through cutting the seeds, outweighed the losses. 

(Image: Paul Smart, Plan Your Patch https://planyourpatch.com/can-you-cut-seed-potatoes-in-half/)

The Norfolk-based organic gardener Bob Flowerdew agrees that dividing up a seed tuber could potetially result in rotting, but you can overcome this by cutting well beforehand and letting the surface heal first.

Andrew Davidson and Niall Mc Allister's blog, Quickcrop, suggests dipping cut potato seeds in wood ash to provide a protective barrier, reducing the chances of rot when they are planted out two weeks later. They also suggest cutting the potatoes length ways instead of across, which will give a better yield as there are more sprouts on one end than the other. 

The College of Agriculture and Natural Resources at the University of Maryland recommends cutting a 6oz (170g) potato into four seed pieces, each with at least one good bud or eye. Then let the cut pieces dry for a few days before planting out to help avoid rot. 

A study by Michigan State University found that cutting the Shepody and Yukon Gold varieties of potato and allowing them to heal, increased yields. Compared to freshly cut seed pieces, the pre-cut potatoes also emerged earlier and grew more vigorously. However, Mountains of the Moon University in Uganda found the opposite. They found that whole tubers yielded a higher harvest 1470g per square metre while plants obtained from sliced tubers yielded a lower 590g per square metre. This experiment used just one variety of potato though (Victoria) and other varieties may give different results. 

Pam Dawling is a British gardener now based in Virginia, and author of 'Sustainable Market Farming: Intensive Vegetable Production on a Few Acres'. She found that cutting large potatoes is more economical than planting them whole. Pam recommends cutting seed potatoes into chunks about the size of a ping-pong ball. She finds that the size of the seed piece has little effect on the final yield. She cuts the seed with a sharp knife once sprouted, ensuring the pieces are chunky rather than thin slithers that would dry out too quickly. She leaves around two sprouts per piece, as more would force the resulting plants to compete. The cut seeds are then planted 1-3 days later in soil that is neither too wet nor too dry, and is at the right temperature for the variety you are growing.

On the whole, it seems to me that it's well worth giving seed cutting a go, so long as the pieces are given sufficient time to heal, and maybe helped along with some wood ash. I'll be experimenting with this myself this upcoming season, and I'll be sure to share the results with you here. Please let me know in the comments how you have got on with cutting your seed potatoes.