Fertilizing
Fertilizing the Soil
Potato onions are heavy feeders and will benefit from some kind of fertilizer. I am 100% organic and I use compost tea, therefore, I have no knowledge of commercial chemical fertilizers.
I have not experimented with fertilizers (other than what I do to all my gardens). Supposedly, potato onions need a lot of phosphorus during the bulbing phase. I've read that you should not feed them nitrogen. Considering that the first half of a potato onion's cycle is vegetative (growing the top greens), I would think that nitrogen would be good during that portion of growth. It's just a guess. Since I get good results, I'll continue doing what I'm doing with the compost tea.
What is compost tea? A blend of organic matter that is brewed into a liquid to boost your soil to optimum health. It is also known as "liquid extract". After the "tea" has steeped for a minimum of 36 hours, the extract is brimming with beneficial microbes/microorganisms (bacteria, protozoa, fungi, micro-arthropods, and nematodes). After seeing that list, hopefully it goes without saying, "Do not drink the tea," because everything in that pail is rotting. And yes, it smells bad, but plants love it!!! I use it in all my gardens and raised beds.
The microorganisms in the tea are alive and need water, air, shelter, and food. The five-gallon pail and compost tea provides all.
Making Compost Tea
The tea can be made with any combination of organic material, e.g., leaves (dead/decaying and live), twigs, compost from your compost bin, straw, grass, flowers, plant-based food scraps (not meat). Fill a five-gallon pail 2/3 full with a variety of organic material, and then fill the remaining space with water to an inch below the brim. The organic material will float and that's fine. Cover the bucket loosely so it can breathe. I keep my buckets in the garden all summer, refilling with a garden hose after I use some.
Using Compost Tea
When I need to fertilize the garden, I pour the liquid portion of the tea directly into a sprinkling can and dilute it - 1/2 compost tea, 1/2 fresh water - do not use undiluted tea directly.
How Often?
I fertilize with compost tea every other week.
At the end of the season, when prepping my gardens for winter, I dump the buckets in various areas of the garden to prep them for spring. I start fresh every season with new compost tea.
Mycorrhizae Fungi: I have read that it's a great idea to inoculate the soil with mycorrhizae fungi, either by applying some spores to the soil or watering with a mycorrhizae solution after transplanting. Mycorrhizae are beneficial fungi that promote healthy root development and nutrient uptake for all plants. However, onions are especially reliant on root-mycorrhizal partnerships to take up phosphorus that is essential for their growth!
As you can see in the video, I did not get larger bulbs from the three different tests I performed: applying it directly to the roots, mixing it in water, and a topical application.
Who knows, maybe I already have a healthy amount of mycorrhizae naturally occurring in my soil and I do not need to supplement.
In the future, I will not be doing any other these three applications to my potato onions.
Urine: Yes, you read that correctly. Admittedly, my first thought was "Eew!" but people use cow and chicken manure, so why not their own urine? Thinking rationally, you know exactly what is in your urine because you know what you've ingested earlier that day.
I only drink well water and home-brewed tea, take no medications, and eat what I grow, therefore, I know exactly what is in my urine.
I have yet to try urine, but some swear by diluting it one part urine to three parts water mixture for fertilizing near their onions, not directly on them.