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.

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