Your article says to plant onion seed indoors in the fall. Can I start seeds indoors now for spring planting this year, or is it better to just plant them outdoors in March/April? I live near Detroit.
If you start them right now, you should still be ok as the weather stays a bit colder longer in northern areas and that will allow them to get large enough for transplanting in time.
When is a good time to plant onion transplants in Dallas?
Around the beginning of April, or whenever the temperatures in your area stay a consistent 50 degrees F. or higher during the day.
What should I use to fertilize onions?
Onions require a high source of nitrogen. Therefore, a nitrogen-based fertilizer (ammonium sulfate or ammonium nitrate) should be applied. For organic gardeners, a rich compost high in nitrogen should be incorporated into the soil.
I've grown onions for 50 years now, and every year try to get them as big as I can, even putting them in early to try and get as much growing time as I can. Still I can never get them as big as some I saw many years ago on a allotment. This bloke had rows upon rows of at least 6-pound onions. I never saw him to ask, but I'm curious as to what he fed them, or if they were a special onion. I try ash and all sorts of feed to get 3-pound onions but never 6 pounds. Do you have any info that could help me?
This article will help you:
https://www.gardeningknowhow.com/edible/vegetables/onion/onion-info-tips-for-growing-big-onions.htm
I would also recommend working in phosphorous into the soil as well. That helps with root growth.
I have had an onion growing in my house for about 3 weeks now, and it has just gotten bigger and bigger. It has sprouts coming from the top of it. I put it in a pot with good soil. Now what do I do to take care of it? Should I put it outside? I think it will turn into a flower.
If the temps are consistently above 50F, you can put it outside. Yes, it will eventually flower. There are some kinds of onions that are actually grown for their flowers.
I'm planting onions inside the house. . . . . how often do they need to be watered?
They will need to be watered when the very top of the soil is dry to the touch. It is going to vary depending on their conditions, but check them daily. Do not let them dry out completely.
So, we have a regular purple onion with a 3-inch green stalk shooting out of the end. We dug a hole and put the onion in the hole. This won't work right? I guess it's already grown. Will this provide a seed for future growth? Was this all just a silly exercise in hole building?
You won't end up with new onions, but, yes, you may end up with seeds or bulblets (seed bulbs attached to the mother plant you can plant next year).
Also, many alliums (onions and relatives) have a lovely flower. You may find it very decorative.