Our very own horticultural expert, Sue Sanderson, recently set up a series of informal potato trials to see which growing method produced the best yield. Using seed potatoes, Sue experimented with different sized tubers, found out what happened when she cut some in half, and compared the modern ‘lasagne method’ with traditional ‘earthing up’. While not conducted under strict scientific conditions, Sue’s trials produced some clear winners. Here’s how our resident expert recommends growing potatoes…
Frequently asked questions about growing potatoes
Harvesting potatoes is my second favourite garden task, beaten only by lifting parsnips! You can feel your excitement building as you lift each tuber from the ground, gently rub it clean of soil, and watch your hoard of spuds grow by the minute.
In my small town garden I tend to opt for potato growing bags that can be easily moved around. The other advantage is that I can just turn the bags out and harvest the crop without the need for any digging! Over the years I’ve been asked for lots of advice about growing potatoes this way. Here are the most frequently asked questions that I set out to test:
- Do larger tubers produce more potatoes than smaller tubers?
- Will I get more spuds if I plant more or less tubers in a potato bag?
- Does the old wartime method of cutting tubers in half really work? (The theory is that so long as both halves have decent chits (sprouts) then they should grow as two separate plants, thereby making your seed potatoes go a bit further. Once cut, they need to be left so that the cut surfaces can dry out before planting.)
- How does the ‘lasagne’ method compare to the traditional ‘earthing up’ technique?
The potato trial variables
By mid April, the trial seed potatoes were chitted and ready to plant. I chose a second early variety, ‘Charlotte’ and on a damp, grey spring morning I planted up the following seven bags:
- Control/ Earthed up: 3 medium sized seed potatoes, earthing up method (no experiment is complete without a ‘control’ test to compare the others tests to)
- Lasagne Method: 3 medium sized seed potatoes, ‘lasagne’ method
- Large tubers: 3 large seed potatoes, earthing up method
- Small tubers: 3 small seed potatoes, earthing up method
- Less tubers: 2 seed potatoes, earthing up method
- More tubers: 4 seed potatoes, earthing up method
- Halved tubers: 1 seed potato cut into 2 halves, earthing up method
The potato trial results
It’s important to note that this trial happened during a very wet summer, and so isn’t applicable to everyone’s growing conditions. Here are the surprising results:
Large tubers vs. small tubers
The size of the initial seed potato doesn’t seem to make any difference at all to the yield. In fact, the smaller seed potatoes produced one or two more tubers than the larger ones.
Conclusion: Who said ‘size matters’? The results show that the size of the seed potato doesn’t influence yield.
More tubers vs. less tubers
One bag was planted up with two seed potatoes while another was planted up with four. There was very little difference in overall yield, however the potatoes from the ‘Less’ bag seemed slightly larger, so maybe it’s better to use fewer seed potatoes and spread them across more bags if you prefer larger potatoes.
Conclusion: Give your seed potatoes more space to get larger potatoes from your bag.
Now this bag was a surprise. Call me a sceptic but I really didn’t hold out great hopes as it only contained one seed potato (2 halves) in total. Whilst the potatoes harvested were not the biggest, the yield was still comparable to that harvested from the other bags.
Conclusion: Larger seed potatoes can be cut in half to maximise yields, so long as both halves have eyes.
‘Earthed up’ planting vs.‘lasagne’ method
I wasn’t expecting this, but the lasagne method was the only bag that outperformed the earthed up control bag quite significantly!
The lasagne method describes planting the seed potatoes in layers in your bag, like a lasagne, with all the compost added in one go. Up until recently, we always recommended that potato bags should be ‘earthed up’. This means filling the bag by a third, placing the seed potatoes on top, and then adding more compost until the bag is two thirds full. Some weeks later, when the foliage appears above the soil, the bags would be topped up with compost to cover the stems and mimic the normal earthing up process used by gardeners outdoors.
Conclusion: In future I will be using the lasagna method. It’s much quicker and easier to plant the bags up, and the yields speak for themselves.
We’d love to know if your trials match Sue’s results. Please share your potato growing stories over on our social channels. For more information and advice about growing your own spuds, visit our potato hub page.
Plants and gardens have always been a big part of my life. I can remember helping my Dad to prick out seedlings, even before I could see over the top of the potting bench. As an adult, I trained at Writtle College where I received my degree, BSc. (Hons) Horticulture. After working in a specialist plantsman’s nursery, and later, as a consulting arboriculturalist, I joined Thompson & Morgan in 2008. Initially looking after the grounds and coordinating the plant trials, I now support the web team offering horticultural advice online. I have a keen interest in drought resistant plants and a passion for perennials, particularly hardy Geraniums. I previously stood as regional secretary for the International Plant Propagation Society which gave me lots of opportunities to see what other horticulturalists were up to in their nurseries and gardens.