Mulching Potatoes With Straw

Rémy Bacher
Tuesday, 8th May 2012

A French-wide investigation comparing potatoes grown under straw mulch against a control test of conventional earthed up potatoes.

Mulching potato plants with straw is a method well known to us, in the world of permaculture. But the question of whether "to dig or not to dig" is not black and white. Certainly, conventional cultivation of potatoes requires a great deal of work (preparing the soil and visiting the potato patch to earth up the growing plants) but it also has its benefits: a beautiful earthed-up ridge promotes the proliferation of underground stems on which new tubers can grow and the risk of the tubers going green is reduced by protecting them from light. 

In the autumn of 2008, staff at the French gardening magazine, Les 4 Seasons du Jardin Bio (The 4 Seasons of the Organic Garden) were captivated by the enthusiasm of Bernard Patry (photo above) a gardener in the Charente-Maritime region, who had experimented successfully with mulching his potato plants. Intrigued by this approach, they asked their readers to participate in a France-and-a-bit-of-Belgium-wide comparison of growing potatoes under straw mulch against a control test of conventional earthing up. 

The garden fork isn’t needed at harvest time with the mulching method and so Rodolph Grosléziat’s potatoes are undamaged. (R.Grosléziat)Mixed results
In general, their readers noted that potatoes under mulch were a bit slower (up to two weeks) to get going which, suggests Daniel Reichenbach, is probably because the covered ground warms up more slowly in the spring.  Slightly decreased plant growth was observed in most cases.

Weeds were less of a problem generally, although Yves Durand and Christine Leveroni—who both have heavy clay soil—found that bindweed proliferated under the mulch.  Some readers encountered a problem of increased slugs and even voles.

In terms of crop yield, a reduction, sometimes significant, was observed in over half the cases, both in the number of tubers and in the total weight per plant. But there were also many success stories. Pascal Chaplault reported: “I used a 20cm (8ins) mulch of straw immediately from planting; the plants took a bit longer to show but it saved me having to add mulch during the growing period. Production was excellent; I got a kilo of potatoes per plant ('Rosabella' variety), which were a nice size and a regular, rounded shape.  The conventionally grown potatoes gave a similar harvest but weren’t so pretty.”  “I picked potatoes ten days before their official maturity: it was a nice moment. I have never had such beautiful potatoes,” wrote Rodolph Grosléziat, “and none of them were damaged by the garden fork, which is not the case when I have to dig them out!”

For readers who enjoyed an equivalent yield between the two methods, the practice of mulching was strongly supported. The ease of harvest was also appreciated: Isabelle Laulon recounts: “In our sandy soil of the Landes, the potatoes were very clean, very pleasant to harvest and was a lovely surprise when we removed the straw.” Damien Meyrand adds: “With mulching, the potatoes sit on the surface of the earth and once the straw is removed, one only has to pull the plants by hand, a child could do it.”

The number of potatoes that turned green through being exposed to light, was more or less the same but, in a fifth of cases, was worse with straw.  However, as Damien Meyrand points out, “As with earthing up potatoes, the care taken in applying the mulch reduces the occurrence of greening.”

The ease of this method won it the support of the large majority of participants. The reduced need to water was another winner. Some suggested that mulching improved their soil, although drawing such a conclusion would probably need more than just one year of observation. 

Two-thirds of the gardeners who took part were motivated to continue with the mulching, feeling that the benefits outweighed the disadvantages.

Row 1 : the control plot with classic method of earthing up. Row 2 : with straw mulch. Row 3 : with a mulch of 5cm (2ins) of compost. (R.Grosléziat)

What now?

A few suggestions to improve the method:

  • Start with a well-loosened soil (particularly important with heavier soils).
  • Plant potatoes 7-8cm (3ins) deep in the ground, i.e., don’t just lay them on the surface. With a better implantation, improved plant development can be expected.
  • Mulch at planting, but not too much (as excessive thickness of mulch at this time was thought to be detrimental) then add more mulch during the growing season.  Bernard Patry, who inspired this survey, explains: “After the euphoria of my first experiment in 2008, the following year's results were less interesting.  My problem came from mulching too thickly at planting, using straw, leaves and grass cuttings. Some plants failed completely, others had trouble getting going and this handicap continued throughout the season in a lower growth. Next year I will just use straw for planting and then add leaves and grass cuttings while the potato is growing.”
  • Yves Durand suggests working in squares (eg 2m x 5m) rather than rows: easier to mulch, less waste.
  • The resource issue of straw was thought to be problematic (following a very dry summer in many regions of France this year, straw production has been greatly reduced).

More generally, consider the choice of mulch, and preferably use the gardens natural resources  (such as leaves, grass clippings, and the output from your garden shredder).  Perhaps even better suited to the purpose, these materials offer a more complete covering than straw, and as they decompose over the season they nourish the soil.  Francois Bonnin underlined the benefits of adding comfrey leaves, which are rich in potassium.

Rodolph Grosléziat compared the use of a mulch of grass (30cm/12ins) and a thick mulch of compost (20cm/8ins) (see photos 4/5 below). The potatoes mulched with compost started faster, with vigorous plants producing a significant crop, and the compost also benefits any succeeding crops which follow over the next four or five years - without the need for further fertilisation. A great way to think of your garden rotations.

Remy Bacher
 

Originally published in the French organic gardening magazine, Les 4 Saisons du Jardin Bio, adapted and translated by Stuart Anderson. 

Les 4 Saisons du Jardin Bio (The 4 Seasons of the Organic Garden) is published by Terre Vivante, pioneers in organic gardening and practical ecology. The magazine, founded in 1980, now has 30,000 subscribers.
http://boutique.terrevivante.org/kiosque-presse/459-magazine-les-quatre-saisons.htm 

Further resources

Experimenting with potatoes

To dig or not to dig. How my allotment made the decision for me

Organic Gardening: The Natural No-dig Way

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Jim Thomas |
Fri, 11/05/2012 - 15:09
My previous attempts at growing potatos using the conventional earthing up method had been nothing but hopelessly demoralising. We have learned that in our near desert conditions in the agean the frost free winters and our dryland techniques work increasingly well in our favour to produce a good rich crop of winter vegetables that in Inglan you could only dream of, and that, by utilising only the sparse rains. But the potatos needed far too much water. They hardly made it above ground before wilting away to an early death, demoralising to say the least. So this year we planted according to a video i was sent by my aussie friends which was a very confident approach to the straw method. We mixed up our own hay, a hybrid meadow of barley, alfalfa and wild flowers with large amounts of compost made from the same source in layers over the seed potatos. One set of rows we buried in a shallow trench of loose earth and the other rows we laid directly on the ground. The straw was piled up to fifty centimeters high and also layered with sawdust to cut the light. As we built it up we sprayed with copious amounts of water and then sat back to watch , no weeding no watering. It took a while for them to break the surface but now they have great canopies of leaves and although it remains to be seen how the harvest will go the fact of having managed it at all is a great success as we have added no extra water and if i plunge my arm in there it is still moist and composty and promises us a healthy addition to our mulching needs for the coming heat. We have yet to harvest but i am already very happy, and am confident that with some reading of the results and tweaking of the system we will be assured of a potato crop throughout the next years. I had no idea i was participating in a franco-belgian experiment but that is the nature of holistic living. The connections never cease to please. Thanks for the opportunity to compare results. This is the video that inspired our experiment...... http://www.youtube.com/watch?v=q1OShZZUt0k
Maddy Harland |
Mon, 14/05/2012 - 14:27
When we started our raised beds at home Tim calculated that we needed to import tonnes of organic matter to fill them. That wasn't our plan so we turned the raised beds into huge composting systems and added whatever we could find - straw, cardboard, composting veg, local horse manure when we had the time and energy to go get a wheelbarrow full, weeds that hadn't gone to seed, shredded paper, clippings, prunings, the dog... well no not the dog but you get the idea - whatever we could find. As a consequence we didn't have much soil to plant into so we planted chitted potatoes in to the mix and simply added mulch and liberal amounts of diluted urine to add nutrients. It worked well and we gained both potatoes to eat and the beds turned into slowly soil. In other beds we filled them with straw etc and then created small pits from compost into which we planted courgettes, squashes and pumpkins. This was less successful as they were hungry plants but we still had a yield whilst building soil.
Bob Segraves-Collis |
Tue, 15/05/2012 - 17:32
For years I have been growing potatoes without mounding up soil. I plant the starts in very loose soil with only sufficient soil to cover them adequately (approx. 2"). As the shoots grow a couple of inches I add a covering of mixed mulch that includes straw, dry grass clippings, dry leaves, chopped green material from the garden, and some moderate amount of compost. The key is to not have material that packs down like soil does over time. Keep adding your mixture as the plants grow. Once the plants are at 6 to 8" tall I start adding a wall along the row made of scrap lumber in the fashion of a raised bed. keep adding the mixed mulching material and building the wall (I try to use the slats from repurposed pallets). Once the plants are on the order of a foot or so high you will find when you reach down into the bed that there are nice little new potatoes growing on the base of the plants. These will appear up the stems until the plants die back in the fall. I find that the potatoes grown this way are nearly blemish free and have an absolutely grand, earthy taste. Enjoy!
Jim Thomas |
Tue, 15/05/2012 - 21:13
Thanks Bob Yesterday i dug up the end plant in a row in a fit of curiosity and was alarmed to find only the small ones at the base as you describe. So now i can expect some action further up the stem......I hope. I fear it is getting hot here for potatos so maybe next year i should start earlier. Hi Maddy Do you know this? Manure free composting method from ww2. http://journeytoforever.org/farm_library/QR/QRToC.html Best wishes for spring time
Caroline Teunissen |
Thu, 31/05/2012 - 15:21
http://www.youtube.com/watch?v=q1OShZZUt0k Because my vegetable plot is very overgrown with weeds (mostly couch grass!) I have planted my potatoes following the method shown in this youtube film. The potatoes have been very slow to sprout, but they were all covered in thick packs of straw. With the benefit of hind sight I should have fluffed up the straw more I think. Anyhow if it keeps the couch grass at bay (for the moment) and I get a crop of potatoes I'll be thrilled.

The

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rtj1211 |
Tue, 30/01/2018 - 12:27
I planted maincrop Sarpo Mira and Desiree potatoes, wrapped in a comfrey leaf, in 2017 in individual holes dug with a copper trowel, about 4-6 inches deep. I earthed up each emerging plant initially using surrounding soil, then mulched with a combination of grass cuttings and comfrey from end June to harvest in early(Desiree)/late (Sarpo Mira) September. After cutting haulms 10 days prior to harvest, I was able to harvest the crop simply by pulling remainder of haulms from the surface and scrabbling with my hands. The beds have been no dig for three years, are a clay soil mulched and composted annually, and show good quantities of earthworms. The tubers were planted in a 40cm grid and yields were c. 20lb per square metre of planted ground. There was no scab and less than 1% of harvested tubers showed damage. For those without access to large amounts of hay/straw, this seems an OK compromise.