Sheet mulching with cardboard and potatoes

This is a technique that revolutionizes the way we typically think of starting a new garden, and the way we typically think of growing potatoes. After learning this technique, it’s hard to go back to the old time-consuming and higher-maintenance methods!

This technique only involves 4 ingredients: cardboard, a knife, potatoes that are starting to sprout, and organic matter like hay, straw and leaves. Inspired by permaculture principles, with this technique you can convert an existing lawn into a new garden patch, and have a harvest of potatoes with almost no maintenance.

How-To

Starting the potato patch garden:

  • Ideally, start in the springtime within a month after the snow has melted and the ground has defrosted.
  • Pick up a lot of cardboard that was destined for the wastestream. The bigger the better. Ideally, visit bike shops or furniture stores to get large pieces of cardboard. If you have smaller pieces, you’ll need a larger quantity to do the technique successfully. Remove anything from the cardboard that shouldn’t be in your garden (tape, staples, etc.).
  • Pick a spot to start your potato patch. You can start the potato patch on a lawn, in a prairie, or in an existing garden. If there is vegetation present (grass, dandelions, etc.) there is no need to remove it. Though, you should flatten any existing vegetation---for example, by placing a piece of cardboard on the vegetation and dancing on it for a few seconds.
  • Cover the parcel with big pieces of cardboard. The underlying plants will be blocked from the sunlight and will eventually die off. You need to make sure that your pieces of cardboard overlap each other significantly (by 30cm or 1 foot). This ensures grass and dandelions underneath can’t manipulate their way past the cardboard toward the sunlight.


Overlapping the cardboard

  • Grab your exacto knife or a kitchen knife. Make an X in the cardboard to create an opening. Add another X about every 25-30cm (10-12 inches).
  • Place a potato in each of these openings. The potato should be sitting directly on the ground (on top of a lawn, for example). Ensure that one of the potato’s eyes is coming out of the opening. Slightly close the opening---ideally the potato should be hidden under the cardboard, with the eye of the potato exposed to the sunlight. The eye of the potato will become a stem and will produce leaves. There shouldn’t be any grass or other vegetation coming out of the opening.


Cutting X’s in the cardboard and adding potatoes

  • Cover all the cardboard with a thick layer of airy organic matter. Hay and straw are perfect, added in a layer about 15-20cm (6-8 inches) thick. The potato eye will eventually make its way through the straw or hay to the sunlight. At the Veganic Agriculture Network, we have never tried this method with leaves... if you try it, let us know if it works for you or not!

Note: if the soil is dry and if rain is not in the forecast over the next few days, it’s recommended to water a little at each step while constructing the new potato patch.

Hay vs. straw: Hay is high in nutrients and will act as a fertilizer when it decomposes, though it may also harbour perenniel weed seeds. Straw should be free from any weed seeds, though it is poor in nutrients. Straw will add organic matter to your soil, but will not act as a meaningful fertilizer. Hay also blocks the light more efficiently than straw, so straw may need to be added in a thicker layer. Use what you have available!

Maintaining the potato patch garden:

The potato patch requires essentially no maintenance. If your layer of straw or hay mulch is thick enough, theoretically you can go on vacation for the next three or four months, and return for the harvest.

Why the straw or hay mulch has to be thick:

  • no weeding: the mulch helps block the sunlight from any underlying weeds
  • no watering: the mulch retains moisture and limits evaporation, so regular watering shouldn’t be necessary except in very dry climates or very dry seasons.
  • no toxic potatoes: if potatoes are exposed to sunlight, they turn green and are toxic to eat. Having a thick mulch ensures that the potatoes are always covered, even if the cardboard begins to biodegrade.

*You may need to add more mulch mid-season to ensure that the potatoes are not exposed to sunlight.

Harvesting the potato patch garden:


Pushing back the mulch and leftover cardboard to harvest the potatoes

This is the best part. As the days get cooler and the potato plants start to look dry and somewhat brown, it’s harvest time. Push back your mulch, lift up the cardboard... and voila! Potatoes! No need to dig---the potatoes are just sitting there, on the surface of the soil, waiting to be harvested.

How is this possible? Because potatoes don’t actually need to grow in the soil. They just need contact with the soil so their root system has access to water and nutrients. Potatoes are typically buried in the soil because they sprout and turn green if they have contact with light. But in this technique, we achieve the same goal of preserving the quality of our potatoes by covering them in cardboard and mulch rather than with soil.

Why to consider this method for starting a new garden

Often when people start a new garden, they remove the top layer (the lawn). The consequences: loss of organic matter, loss of topsoil, loss of microbial life. Gardeners often then dig or till the underlying soil, and then leave the soil exposed for the season. The consequences: an inhospitable environment for soil fauna, increased erosion, and dry or caked soil on the surface.

In ecological gardening, we need to think outside the box. Or, more fittingly, we need to think about the box. Covering the existing vegetation (lawn) with cardboard boxes brings the advantages we seek, without any of the problems.

  • Building our soil: Rather than removing the grass and weeds, we leave them in place. They become our first layer of compost. The cardboard will eventually biodegrade, and the straw and hay mulch will biodegrade in a season or two. These also provide organic matter for the soil. Instead of tossing out our soil, we’re building it up.
  • Supporting soil life: Instead of removing or disturbing the valuable microbial life in our soil, we’re providing them with a suitable habitat and sources of nourishment. In turn, they’ll make the soil more fertile and improve its structure.
  • Protecting the soil: With a thick mulch in place, there is little chance of erosion. The soil will remain humid and have a more steady temperature.

So, what’s the catch? Can this potato patch method fail? That depends on your goals. If you have poor soil quality, compacted soil or a heavy clay soil, you can’t necessarily expect a great potato harvest, and you may be disappointed by the results if your main objective is eating potatoes. However, over the coarse of the season you will have improved the quality of your soil both in terms of organic matter content and soil structure, so the land will be easier to work with and more fertile when you begin a more diversified garden the second year.

If you envision having a large garden, you can start a portion each year using the potato patch method. This method is also appropriate for preparing the land for trees, shrubs and forest gardens.

Why to consider this method for growing potatoes in an existing garden

The traditional way of growing potatoes involves digging the soil to loosen it, creating a trench, and burying the potatoes in the trench under the soil. During the summer, to ensure that the potatoes aren’t exposed to light (since they would become green and toxic), more soil is hilled up around the potato plants on a regular basis. At the end of the season, the soil mounds are disrupted to dig up the potatoes. Overall, this technique involves more presence and energy from the gardener over the coarse of the season. And working the soil will deplete the soil of nutrients and microbial life, while leading to increased erosion.

The cardboard method may require more involvement during the initial planting (finding cardboard and hay or straw), though afterwards the technique is incredibly low-maintenance, with essentially no weeding or watering. For gardeners who enjoy the ease of a low-maintenance garden, this is a much easier way to grow potatoes. And, most importantly, the soil is protected from erosion, the soil structure is improved, and the microbial life is supported.

This is also a great technique for dealing with weedy patches in an existing garden: instead of removing the unwanted plants by hand, you can simply stifle them by covering them with cardboard and organic mulch, while reaping a harvest of potatoes at the end of the season.


11 May 2013
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