Sue’s (Very Unscientific) Potato Trials

Sue’s (Very Unscientific) Potato Trials

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 minute by minute.  In my small town garden I tend to opt for potato bags that can be easily moved to give them sufficient space – particularly as the top growth starts to get a bit wild.  The other advantage is that you can just turn the bags out and harvest your crop without the need for all that digging!

Annie, potato trial supervisor extraordinaire

Annie, potato trial supervisor extraordinaire

Once a fortnight I run a horticultural Q&A session on Thompson & Morgan’s Facebook page and every spring I receive a heap of questions about growing potatoes.  So this spring I decided to conduct a few experiments – just for my own curiosity really, but I think the results are worth sharing.

Potato trials - the traditional method

Growing potatoes in bags – the traditional method

The trials were pretty simple really; a comparison of yields to answer the following burning questions:

  1. Do larger tubers produce more potatoes than smaller tubers?
  2. Will I get more spuds if I plant more/ less tubers in a potato bag?
  3. Does the old wartime method of cutting tubers in half really work? (The theory is that so long as both halves have decent chits 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 a bit before planting.)
  4. How does the ‘Lasagne’ method compare to the traditional ‘earthing up’ technique?
Potato trials - the lasagne method

Growing potatoes in bags – the lasagne method

Now, I realise that this requires some explaining. Up until last year we always recommended that potato bags should be filled by one third, a layer of potatoes placed on top, and then more compost added so that the bag is two thirds full. Some weeks later, when the foliage has appeared above the soil, the bags would be topped up to cover the stems and mimic the normal earthing up process used by gardeners for many years. However one of our directors had tried a different technique; the ‘lasagne’ method!  Basically the tubers are planted in layers and the bags filled up all in one go, with no earthing up to be done later.

Potato trials - More vs less tubers

More vs less tubers

By mid April the seed potatoes were chitted and ready to plant. I chose a second early variety, ‘Charlotte’, just because they were on a special offer – I love a bargain! On a damp, grey spring morning I planted up the following 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

Potato trials - Large vs small tubers

Large vs small tubers

The results are in!!

Now I must admit that this year I didn’t have the time or energy to give my garden the attention it deserves, so the trials received a splash of water now and again when I remembered.  Not that they went short of water – this summer was one of the wettest I can remember.  In fact, I was fully expecting blight to ruin the crop, but by some miracle they were spared. Nonetheless, from chatting with other gardeners it seems that this year was not the year of the spud! In fact, this year yields were shockingly poor, although what I harvest have was of very good quality.

So… excuses made, here are the results:

Potato trials - large tuber results

Large tuber results

Potato trials - small tuber results

Small tuber results

Large tubers vs. Small tubers: It didn’t seem to make any difference at all. 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 it doesn’t

Potato trials - more tubers results

More tubers results

Potato trials - less tubers results

Less tubers results

 More tubers vs. Less tubers: Once again, there was very little difference. Actually, the potatoes from the ‘Less’ bag seemed slightly larger so maybe it’s better to use fewer seed potatoes per bag and spread them across more bags for maximum yields.
Conclusion: Give your seed potatoes some space. Sometimes less is more!

Potato trials - halved tuber results

Halved tuber results

Halved tubers: 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.

Control/Earthed up results

Control/Earthed up results

Potato trials - lasagne method results

Lasagne method results

Control/Earthed up vs. ‘Lasagne’ method: The big success story of my trials. I wasn’t expecting this, but the lasagne method was the only bag that outperformed the control bag quite significantly!
Conclusion: In future I will be using this method. It’s much quicker and easier to plant the bags up, and the yields speak for themselves.

Sue Sanderson
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’m a regional secretary for the International Plant Propagation Society which gives me lots of opportunities to see what other horticulturalists are up to in their nurseries and gardens.


  1. Henry the Poacher, 28th March 2016
    When I was at school during the 1950s my Dad always cut the larger tubers in half with chits on both ends. This was to make them go further (we were a low income family). Instead of drying the cut surfaces, as you have suggested, he just used to dip the cut face in soot or wood ash “to keep the slugs away”. I don’t think it often failed. I’ve been growing my own veg for most of the past 40 years, and have used this method where required. I simply keep the largest tubers with lots of chits to the end of the last row, in case I’ve miscalculated and don’t have enough, then cut the final two or three to make up enough to complete the row if required. I’ve found it usually works OK, and there is no difference in the yield, each half producing the same number of spuds as if it were a whole tuber.
    I haven’t tried the lasagne method in a bag or tub, but I would definitely say that you will NOT get a higher yield per tuber by packing more into a given space, as each tuber needs a specific volume of soil to produce its best. If they have to fight for space, the overall production will suffer. I have found this to be the case when I have grown early earlies in plastic tubs to avoid frosts.
    I hope this may help.

  2. Thank you for all these interesting facts about potatoe growing. I would like to try the lasagne method in open ground, and wonder if this could be successful ? I welcome your thoughts !

    With best wishes,


    • That’s an interesting idea for a small vegetable plot. I’ve never even thought about growing them in this way in open ground. It would certainly be interesting to try.Perhaps you could do your own potato trial with one row of lasagne method and one row of single tubers. I’d be fascinated to hear how you get on.

  3. Thanks for a really informative blog. I am going to have a go this year with the lasagne method, but I’m going to use all 5 tubers. I will let you all know the result
    Give my love to Annie!

    • Rebecca Tute

      Good luck Yvonne, let us know how you get on!

  4. Interesting thank you Sue. I have used the lasagne method for several years and always been pleased with the results.

    • Yes Steve, it certainly seems to be more successful than the traditional method… and a lot simpler too!

  5. Thanks for all this very straightforward advice, I think I am going to try growing some this year, and have ordered Charlotte potatoes, one of my favourite varieties from the greengrocer: I hope the homegrown version will be even better!

    A friend has bought himself some seed potatoes too, so I am sending him a copy of your instructions plus a few grow bags. We will have a contest to see whose crops produce the most!

    Thanks for a very practical, easy to follow guide.

    Sincerely yours, Eunice.

    • It’s great to hear that you are going to give it a try. Best of luck. Let me know how you get on and which of you wins the potato growing contest!

  6. Thanks to all who have tested and tried different potato growing methods. This 2013 year has been my first to have a go at spuds in a bag. The earth up method was used and won a few lovely tasting potatoes. Next year will be the lasagne method. The reason for this post is to encourage others to have a go. The taste of newly lifted spuds is unbelievable.

  7. Great blog! I see that the advice that T&M are giving is for 5 tubers in a bag, lasagne style (love that term!), so i’d be interested to try that along with your 3 tuber per bag to see if the yield differs. I’d also be interested in how different types of growing matter affect things. I can’t re-use my tomato growing bags, obviously, and it’s not very cost effective to buy in bags of compost each year for the potato planters. I’m also left with an excess of blight-infected Solanum family compost that is more than I need to grow anything else. Finally got hold of an allotment this year so i’ll have more space to grow things and can therefore rotate properly. I’m also hoping to grow the Sarpo collection, if it comes back into stock, and hopefully avoid blight altogether.

    • Sue Sanderson

      Hi Nyck, thanks for your comment. Do let me know how your 5 vs 3 tuber test goes – I’d be very interested to hear how you get on.

  8. Hi Julie. I used two tubers at the bottom and one further up for the lasagne method. I think that giving them a bit more space certainly does seem to help and this seemed to be backed up by the results of the ‘more vs. less’ experiment.

  9. In the Lasagne method, I see that you used three tubers. How did you layer them? Two at the bottom and one further up, or each one on a separate level? Do you think that giving each tuber a bit of extra ‘elbow room” using this method was what increased the yield?


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