Brussel Sprouts can be a challenge. For you area your timing seems to be about right. Catskill has never done well for me and I have not grown Falstaff. They slow down with waning daylight so expect a much longer season than 90 days. They will stand a light freeze. In fact they are good until the ground freezes. In zone 6 (southwest Virginia) I pinched the terminal bud at Thanksgiving for Christmas harvest (Prince Marvel). They usually transplant well if the plants are vigorous and hardened at time of transplant. They are heavy feeders and like a good amount of N.

Hi Kim! I have grown Brussels the last 3 years. 2 good and 1 failure. I am not a master by any means but I will give you my opinion. They are very heavy feeders, this year I put a good amount of manure in the garden (actually last fall) and got great results compared to last years failure. I don't see when you started your seedlings but mine were in the ground the end of may. The sprouts take a while to form and are best after a freeze or 2 sweetens them up. The transplant problem may well be a hardening issue more than a variety one. I would not expect much more growth this fall, but you never know.
For what its worth,
Bill

Thank you both! I have probably haven't been feeding them enough.

Also, I think I will try a different variety of Green seeds next year. I believe I read the Bubbles and Jade Cross were two varieties that people had the most success with.

I highly suggest a hybrid when it comes to sprouts...it's one area where hybridization has excelled over open pollinated choices.

Some may disagree, but they probably have growing sprouts down to a science or they're blessed with ideal conditions.

Have you been taking off the bottom leaves, maybe 3-4 a week? That triggers the formation of the bottom sprouts. Last week I pinched out the tops to further speed things along. You may make it yet.

This is my second year trying sprouts, but last year we were drowned out, so I suppose it didn't count.

I started Jade Cross from seed and had them hardened off and in the ground by late May here in zone 2. That's five or six(ish) weeks ahead of when you got yours in in zone 5. Our soil isn't the greatest and they had no fertilizer beyond what we applied to the entire garden in the spring and a targeted dose of soluable synthetic a couple of weeks after transplanting. I topped the plants in mid-September. The sprouts are nice, but not huge. If I can get them in even earlier and keep them better weeded, I think they'll get nice and big, closer to typical size.

Planatus, no. Not a single site I visited on "how to grow sprouts" told me to do that. I suppose it makes sense, because every picture I've seen of a mature plant only has leaves on the top; yet I never put two and two together.

Thank you!!

I put mine under plastic today. With the cold wx tonite (upper 20Fs) and just small sprouts forming, I decided I better protect in hopes of pulling out a crop yet.