The few times I grew BSs they were planted in the Spring and produced well by late summer. It may be that they produce better with a longer growing window than autumn permits as daylight hours get progressively shorter? I've never grown them in the autumn so this is just a guess.

Yes, that’s what I was thinking. By August sprouts should be good sturdy plants, not just being started. They need a long growing season. In my climate they're a late Autumn, winter and early spring vegetable. They're sown in spring and planted out in May and June. I don’t know how they’d fare in a Chicago winter but since yours look healthy I’d just leave them and see if they survive to produce sprouts in spring. btw they grow very large and need several feet of space around each plant. Yours look rather crowded. Also why have you cut so many leaves off? If they do not produce any sprouts the tops make great greens which, personally, I prefer to the sprouts themselves.

Planting brassicas for Autumn is a race against Winter, and yours didn't finish before the cold, dark days. They may survive the cold and grow again in the Spring, but they might flower next year instead of making edible sprouts. You could always try and see what happens, it's not like you are going to plant something else there in December.

As for what went wrong? I would agree that they are pretty crowded. Better to get a few big plants than many smaller plants. Are they in full sun? They need full sun, especially since the days are short in Autumn. Otherwise, they look healthy but should be bigger plants by November.

I planted eight seeds in early August and they all grew nicely. When I planted the small plants in the box I had tomatoes in there already so I had to put them in the front and in between the plants. I pulled my marigolds to put the brussels spouts in the box. The plants are in full sun all day, that is when the sun shines. I was thinking the daylight must be the reason they won't grow anymore. The plants all grew after I put them in the box but then they just stalled. I cut the bottom leaves off because I saw a lady saying it would help the production of the sprouts. I guess that was wrong!! The type I planted are catskill and the day I transplanted them was 9/16 so I am gathering that was not an early enough date to put them in the box. I will try them again in Spring but I will start them indoors or I will wintersow them. I assumed that our crazy weather that was warm for all of October would have helped them grow. At this point I will not touch them until I can't stand looking at my failure! I hope they don't freeze solid before then. Next week we have preditions for 60 degrees. haha!! Maybe they will have a growth spurt.

Here in the KC area I start my fall Brussel Sprouts from seed in late June and plant them out by Aug 1 and they usually have nice sprouts to harvest by Thanksgiving. Up in Chicago I think you would need to move up that date by a few weeks or so or even plant them out as a late spring crop in May to give them even more time.

I also didn't have luck getting good sized sprouts from heirloom varieties like Catskill and a couple others so I switched over to a early hybrid variety called Jade Cross and it has done well for me each year I've grown it.

Don't want to beat a dead horse, but as others have already stated, they were started too late. Brussels sprouts should be Spring planted in our climate. The plants need wide spacing; I wouldn't use less than 18". They will grow tall all summer, and begin producing sprouts late in the season. Snapping or cutting off the lower leaves may be helpful. The sprouts are best harvested after a frost, when they will sweeten & become less bitter.

All is not lost this year though. You can still eat the nutritious greens, recipe suggestions are available online.

I am new to brussels sprouts and I will say I lived and learned this time around. I will try again but understand now that the ones I will plant at the end of Spring will not be mature until Fall of the same year. WOW!!! That is a long grow time.

@LoneJack Zn 6a, KC - I will certainly find a shorter season variety to try in Spring.

I want to thank everyone for the comments and help. I will always be a gardening "work in progress". :-)