What are potato onions?
They are perennial multiplier onions in the same family as shallots (Allium Cepa var. Aggregatum), but are larger, rounder, have a more intense flavor and store better than shallots.
The potato onion reproduces by division of bulbs rather than by seed - although they do produce seed some years. One bulb planted will produce 3-8+ onions of varying sizes during a season. Bulbs typically range in size from one to three inches (2.5-7.6 cm).
Simple Answer: If you plant one potato onion bulb (mother) it produces an average of five identical clones (daughters) of itself in a cluster (nest) that sits on top of the ground. From those five daughter bulbs, you replant one and eat the other four, repeating every year. Easy and sustainable!
Common Names: Potato onions are also commonly known as nesting onions and multiplier onions, and less frequently as hill onions, ground onions, underground onions, tater onions and mother onions.
Note: since potato onions and shallots are virtually indistinguishable, from a genetic standpoint, all of the information I provide about potato onions - from planting to harvesting and curing - also applies to shallots.
Why are they called potato onions?
No one knows for sure. The most likely answer is because they reproduce similar to potatoes, where you plant one potato and get many. The difference is that potatoes grow down in the soil, whereas the potato onion clones nest on top of the ground.
Do they taste like potatoes?
No, not at all. They taste like onions. Yellow potato onions are pungent when raw, making my eyes water while cutting them, but cook/caramelize fairly sweet.
Onion Sets, Walking Onions and Pregnant Onions are Not Multiplier Onions
Onion Sets: Multiplier onions and onion sets are not the same thing. Onion sets are biennial onions that are always started from seed. Multiplier onions are commonly started by planting bulbs rather than seed. Potato onion bulbs can be replanted indefinitely and harvested annually, whereas biennial onions must be grown each year from seed.
Walking Onions: Likewise, walking onions are not multiplier onions. They are classified as Allium Cepa var. Proliferum and also known as Tree Onions, Top Setting Onions, Winter Onions and Egyptian Onions. They produce bulbils on top of a stalk (photo right), and when a bulbil is planted, it will produce a single onion.
Pregnant Onions: I've seen some occasions where potato onions are call "pregnant onions". Pregnant onions are actually succulents (ornithogalum caudatum), not a multiplier onion.
What's the difference between the various colors of potato onions?
There are five colors: yellow, brown, white, red and Green Mountain. Brown is considered a sub-class of yellow.
Yellow/brown are the most strong/pungent when raw, but tend to cook the sweetest (that being the case with my long-day yellows). It is my understanding that long-day onions contain more sugar than short-day. I, personally, will never know because I will always grow at this latitude. Generally, bulbs are 1-4 inches (2.5-10 cm) in diameter. Yellows/browns store the best, with browns keeping the longest. Yellows are the most common potato onion; most vendors sell yellows.
Differences in sight, aroma and taste between the five varieties of potato onions and shallots that I grow.
White are less strong than yellows but more pungent than reds. They are the most difficult to grow, being susceptible to numerous diseases. Also, they do not store well long-term.
Red are more mild than yellow and white, but still pungent, and is probably best to eat raw. They store poorly. Red potato onions from the 1800s were red skinned with purple and white ringed flesh. I'm hoping a red potato onion will grow from the Green Mountain potato onion seed I purchased so I can compare it with the Dutch Red Shallots.
Green Mountain is a highly sought after variety that grows larger than other colors of potato onions, more akin to commercial size onions. I purchased both Green Mountain true seed and bulbs and will plant them for the 2024 season. I'll update this when I have more experience with them.
Climate
Onions are hardy plants that originated in cold climates. They grow well in temperatures as cold as USDA Hardiness Zone 4 and perhaps colder with a thick top mulch and/or snow cover. Multiplying onions and other perennial strains are typically hardy to -26F (-15C) when given a protective winter mulch. If you're unsure, check the 2023 USDA Plant Hardiness Zone Map. It changed during 2023; they readjusted my location from 5A to 5B.
Light Sensitivity
Most potato onions are long-day plants, and only produce sizeable bulbs north of the 37th parallel. It is my understanding that there are some short-day varieties of potato onions, but I am not familiar with them.
Long-day varieties will begin bulbing when day length reaches 14-16 hours.
Intermediate-day will bulb when days are 12-14 hours.
Short-day bulb when days are 10-12 hours.
Planting short-day in northern states will cause early bulbing without much vegetative top growth. Bulbs will be small because there isn't enough foliage to produce the bulbs.
Planting long-day in the south, they will likely never bulb because days are too short.
You should be able to plant either long- or short-day bulbs in the intermediate zone.
From what I've read, there are varieties of potato onions that will grow in every state except Florida and southern Texas.
My advice is to purchase from a seller within the same day-length zone as you. If you're above the 37th parallel, purchase from vendors who are north of it. If you're below, then sellers who are south of it.
Easy and Sustainable!
Growing potato onions is extremely easy! In its simplest form:
Keep the best to re-plant the following season
Eat the remaining bulbs and enjoy!
Repeat!
Interested In Trading Potato Onions?
I know zero about genetics, so it is mere speculation when I say that I suspect the majority of potato onions in the USA are most likely genetically related. I know there are genetic accessions out there in the world that do not exist here in North America. I'm interested in expanding the diversity of my potato onion gene pool and I would be open to trading potato onions bulbs and/or seeds, if you are on a continent other than North America. If you have no interest in trading, but would like to contribute a few bulbs/seeds, I would gladly cover shipping costs.
Thank you!
I hope this information has been helpful. I will update it as I make new discoveries on my potato onion journey.
