Thank you for your questions. I get excited this time of year as vegetable gardening has been in my bones since I was ten years old.

Onions (including shallots) in general are great to grow in our gardens. Since you are starting from seed, you might consider starting the seed now in late January. Onions are a cool weather crop and can be transplanted to the garden as soon as the ground is workable. For much of the Ohio region, this would be around mid March rather than May. You are free to wait until May but I wanted you to know that you can do so much earlier.

Although much of the guidance states that it takes 90-100 days from seed to harvest, it truly is weather dependent. Although I transplant in mid-to-late March, I harvest between early July and early September. If I see the onions start to bolt, I’ll harvest sooner. Bolting is indicated when you observe a seed stalk forming and producing a flower (which then produces seed for next season). 

As for saving seedlings to plant next year, in theory it should work. However, maintaining proper hydration (not too dry, not too wet) is critical. It’s worth a try. 

The best results I have had with onions is when I buy seedlings from my local garden center. You won’t find onion seedlings in any of the big box stores. The local garden center that I purchase onion seedlings from is locally owned and stores 4-6 cases in a refrigerated cooler. Their source is Dixondale Farms in South Texas. When I grew vegetables for the purpose of selling at Farmers Markets, I bought directly from Dixondale. Although it’s pricey, the results are praise worthy.

Here is a link to a site with very good advice on growing onions and is backed by university research and experience: https://extension.usu.edu/yardandgarden/research/shallots-in-the-garden

I hope this answers your questions but if not, please do not hesitate to reply to this email and ask. I am always happy to help any home gardener.