Hilling Potatoes in Raised Beds

While gardening in raised beds has many many advantages over the traditional wide open row garden, there are a few crops that pose logistic challenges.  One of these is potatoes.

Potatoes are traditionally planted in rows in a field and the soil between the wide rows is raked up towards the plants as they grow to form hills.  People say if you continue to hill, you will get more potatoes per plant because the plants will continue to put out higher layers of tubers as the soil deepens.  This is the theory behind most container style methods of growing potatoes

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The most fantastical method of container growing potatoes in layers is the spud box.  The theory behind this is that you plant the seed potatoes in the bottom, and as the plants grow, you add layers to the box and soil to cover the potatoes.  When you are ready to harvest you open up the side and the bounty of spuds just spills out.  And because you have been able to cover your plants so much deeper than a traditional "hill" you will have exponentially more potatoes to harvest.  Well... yes and no. 

A vintage Henry Maule seed catalog gives a cutaway view of a hill of potatoes.

While I do like growing potatoes in containers, I've never found that I can get more yield by burying them deeper.  In my experience, most seed potatoes will produce six to eight new tubers and the growing conditions will determine how large these grow. It is just easier to harvest them from a container without digging with a fork risking damage to the potatoes and inevitably leaving some behind.  Maybe I'm just not doing it right?  Maybe you have to believe and I just don't have faith in the "more potatoes" concept.

There are two good reasons to hill your potatoes.  First is to support the tall plants and prevent them from laying flat on the ground contracting diseases.  The second reason is to ensure the tubers are thickly covered with soil preventing them from turning green in the sunlight.  Green potatoes have a high concentration of the gkycoalkaloid called Solanine.  This is a toxin produced by the nightshade family and it will give you a very upset tummy.  Even if you cannot see the green color on the skin, there will be a green layer just under the skin and the potatoes will taste like soap.

In a farm setting, you would need implements to hill acres and acres of potatoes

When I first started growing potatoes I had sort of a "mini field" set up.  Yes, there were space constraints but I didn't really have a depth limit so I could still add or remove material as necessary.  This isn't true in a raise bed.  Once its full its full.  You can mound it up in the center but that will just cause unwanted water run off.

The two necessary components to hilling potatoes is room between the rows (not only to supply the material needed, but to allow the inevitable widening of the row) and deeply tilled, loose soil that can be easily moved.  When you get down to hardpan you are out of material

Hilled rows of potatoes can pose a problem when watering.  The water will initially run off of the hill.  You need those wide rows and loose soil to hold the moisture long enough for it to sink in before running away.

Valleys for planting built with hilling material collected between the rows

When you plant potatoes in a raised bed you have to plan your hilling material ahead of time because you can't necessarily just add more material when you need it.  Which means you have to start with valleys and end with hills.  You are going to plant your seed potatoes as much lower than your finished bed level as you can manage, and you can store your hilling material between the rows of potatoes because with a raised bed you are not going to be walking on it and compacting it again.

With a rake I've created these valleys.  

And now I am going to dig my seed potatoes about six inches into the bottom of the valley.  I stopped there because after that point my soil is a higher concentration of clay and even if you dug the seeds down into this harder material the plant would have trouble putting roots out through it anyway.

As you dig the individual holes, you can add the additional material to your hills.  You won't need all of it because I just sort of brush the loose soil from around each side of the hole onto the seed potato just enough to block the light and let the plant know it's time to grow..

As the sprouts form, you can begin to first level your bed and then eventually form the hills.

You should let the plant keep at least three inches of growth above your soil level

These plants are ready to hill again.

I now use a rake to take about half of the ridge of soil 

in each direction towards the rows on each side.

You keep working over the same area until the plants are supported with hills, and you are now left with the valleys between your rows.

In the spring it only takes a day or two to get enough growth to hill again.

Sooner or later you will run out of material.  The wider you spaced your rows, the wider your hills can be.  At this point you need to be watchful that you are not hitting roots with your rake.

As your plants continue to grow, keep an eye on things to make sure your potatoes aren't growing too close to the surface.  Rain erosion can wash some of your hilling away exposing the potatoes.  If the potato patch is too dense to use a rake to re-cover your spuds, an good emergency fix would be to add a layer of straw. The straw can either be removed at the end of the season or tilled into your soil.

And that's how I deal with hilling potatoes.  I've grown them in a variety of locations and containers and this method in this bed gives me the best results every time.  

Within a week my plants should be blooming and I will be able to take some new potatoes away from the edges without disturbing the plants