Ok, full disclosure, before reading Pam Dawling’s book, Sustainable Market Farming, I had no idea what a potato onion was. In fact, I didn’t even know that such a crop existed.

This is yet another reason why continually educating yourself is so important. Without reading all of the amazing and helpful books I have read in order to help prepare myself for the upcoming market garden season, I would be in deep doo-doo, if you catch my drift.

The more I read about potato onions, the more I thought, “Hey, we should be growing these.” I will tell you why I felt that way in just a couple of minutes down the page.

What Are Potato Onions?

Potato onions are a type of multiplier onion, a traditional heirloom crop that also has curiosity value for market booths, CSA’s, and growers themselves. 

Gourmet chefs can also provide a local demand. 

Potato onions are also known as hill onions, mother onions, and pregnant onions. 

Planting a mix of sizes of potato onions ensures that the grower gets both an edible crop and seed bulbs for the next year. 

Barring disaster, you never need to buy new seed stock.

Potato onions do not start from seeds, so the whole job of starting seeds and transplanting is avoided. 

This crop has a big appeal to those interested in local food, sustainability, permaculture, and perennial crops.

It means independence from Monsanto and other large seed conglomerates. 

These are the reasons why I am excited to grow potato onions this year!

The larger seed onions are planted in the fall. They grow and divide to produce a cluster of small bulbs, which can be replanted the next fall or winter. 

Small onion bulbs are planted in late fall or winter and most simply grow larger and produce a single bulb. 

Some small bulbs may grow and divide into a cluster of medium-sized bulbs. 

The largest bulbs are the food crop and the smaller ones are mainly a seed crop. 

Advantages of Growing Potato Onions

Another advantage of including potato onions in your crop portfolio is a spreading out of the workload. 

Planting happens in fall, winter, or early spring, and given good mulch, little work is needed until harvest. 

Potato onions provide some early onions for sale. It’s good to get the largest of your potato onions eaten right away, as they don’t store well. 

The rest of the crop is spread out on racks to slowly mature and can be picked through for more eaters/sellers once a month or more. 

The curing and storing stage is a low-stress job, and the work can be done on rainy days, or during the heat of the day to help you stay out of the sun. 

Yields can be three to eight times the weight of the seed stock, depending on growing conditions. 

Individual bulbs can be grown indoors in a pot to produce a steady supply of green onions during the winter. 

Varieties

There are various regional varieties that you may try that are suitable for your growing area.

Pam grows the most common one, the Yellow Potato Onion from Southern Exposure Seed Exchange. 

Their Multiplier Onions Starter Package includes a four-page “Garlic and Perennial Onion Growing Guide.” This guide is also available on their website. 

Crop Requirements

Required soil conditions for this crop are the same as for other onions.

The main distinguishing factor is that the ground needs to be available in fall, so avoid sowing winter cover crops where you intend to plant. 

In Pam’s area, they grow one or more food crops that mature by the frost in mid-October, then prepare the soil and roll out hay mulch to prevent weed growth. 

At planting time they roll back the mulch, plant the onions, put the mulch back on top, and let them do their thing all winter long.

After the potato onions are harvested in early June, and as long as the soil fertility is kept up by spreading compost,  they plant more food crops such as lettuce, fall greens, late carrots, beans, squash, or cucumbers. 

Planting Potato Onions

The smallest potato – below 1.5” diameter –  store longest, and are best planted after the winter solstice and the hardest weather, as the small plants are more prone to winter killing if planted too early. 

Pam plants in a mild spell in late January or early February, four to five inches apart. This way not everything is lost if they have an unusually cold winter. 

However, larger onions are best planted earlier, or they will sprout and rot before you get them in the ground.

Pam plants her largest ones (over 2”) in September, 8 inches apart.

Their medium-sized ones (1 1/2 to 2” in diameter) get planted in mid-November at 6 inches apart.

As a general rule, you plant in October in northern areas; December in southern areas, and Florida and Southern Texas are too hot to plant at all.

If you are the Pioneer for this crop in your area, and you have no Old-Timers to consult, you’ll probably have to experiment a bit at first.

Always save some for spring planting, even though yields from fall plantings are significantly higher.

Don’t risk having all your onions killed by unusually cold weather.

Initially, you might want to maximize the yield per onion from your brought-in starter pack by using wider spacings and getting larger onions.

The following year you can plant these larger ones and get lots of smaller ones. 

When planting, Pam draws furrows deep enough to cover the onions with 1 inch of soil, sets them by hand, then hoes to cover and roll out hay mulch. 

The onion shoots will make their way up through the mulch, and she finds it worthwhile to ‘rescue’ any shoots that are trapped under thick clumps of hay, once it looks like most of them should be emerging. 

Potato onions can withstand sub-freezing temperatures in every area of the continental US when suitably planted and mulched. 

For spring planting, leave the top third of the bulb exposed, to reduce the chance of rot. 

Pests and Diseases

There are not a whole lot of pests or diseases that affect potato onions, fortunately. 

Harvest

When the top starts to die, lift the onions gently and take them to cure.

If planted at the correct depth, the bulb cluster will be at the soil surface, and you won’t need a fork to dig them.

They will not all be ready at once. Harvest the mature clusters once every few days.

Leaving mature bulbs exposed to hot sunshine will lead to rot. 

The fall planted ones will tend to be ready a week or two before those planted in late winter. 

Do not break up the clusters at this stage, as it encourages sprouting. 

Pam does not cure her onions outdoors as they can get sunscald.

They cure on slotted racks that stack on each other leaving space for air in a barn with fans, for at least a couple of months. 

Onions bigger than 2.5” diameter are best moved along to dinner plates within a couple of weeks of harvest.

If you want to plant these largest ones, refrigerate them immediately and plant them in September. 

Curing and Storage

Curing for a couple of months is important to develop flavour and hardiness. The weight after curing for one week is about twice the final dry weight after trimming. 

Aim to sort through your potato onions once a month, starting a few weeks after harvest. Remove any rotting or sprouting onions each time you sort. 

At the late June sorting, take out any onions larger than 2” diameter for eating. 

If you are on a fast-track to increase your crop, you can refrigerate these along with any you stored immediately after harvest, for September planting. 

Eat them or plant them, the large ones won’t keep long. 

At the late July sorting, remove any rotting onions, either individual onions from a cluster or whole clusters. 

In late August, separate the clusters, trim the tops to 1”, and sort the bulbs by size. This will help you figure out what to save for planting and what to eat or sell as seed. 

Pam sorts smalls (less than 1 ½”), mediums (1 1/2 to 2”), and compost material. 

The rack space required after this stage is only a third of what it was before. 

In mid-September, Pam decides how much to keep for planting.

She leaves the onions in a single layer on the racks. The small ones stay there till late January, through freezing conditions.

Ideal storage conditions are 32 to 40°F (-1 to 4.5°C), 60 to 70% humidity, with good ventilation. Layers should not be more than 4” deep. 

Seed Saving

This is a natural part of growing potato onions.

This is how Pam saves her seeds:

She started with half a pound of seed stock, planted one spring.

They only harvested a pound and a half that first-year, partly because of the late start.

They kept it all for seed stock and planted more each year in a 1:2 or 1:3 larger: smaller ratio by row length.

This was done to get enough small and medium onions to plant the same area the next year and to get lots to eat as well. 

When their focus changed to growing for seed stock they started to sell all the small ones and plant a bed each of large and medium ones, in order to get the most seed stock.

If you don’t end up growing for seed stock, and focus mainly on eating and planting potato onions, you can continue to plant the smaller ones after the winter freeze.

Bottom Line

I think potato onions are a great low-maintenance crop to grow, eat, sell, and grow again!

Their sustainability is what really drew me to them, and the fact that you can even sell the small bulbs as seeds is another interesting revenue source for growers.

I honestly have no idea if these are big money makers for growers, I am assuming they are not since they are not widely grown, at least in our area. 

However, if local, sustainable, low-maintenance plants are on your checklist for crops to grow, I would give these a shot.

I had not intended to grow potato onions this year, as I am just finding out about them now, but after doing this research, I do plan on buying some to plant this fall to see what happens.

Do you think potato onions are worth growing? Let us know in the comments below.

Stay Local,

Kathy & Jon

your friendly neighbourhood growers