One other thing no one mentioned is that many brussel sprout varieties mature differently. There are early, mid and late season ones. "Long Island" seems to be listed as a mid. Last year I grew "Cumulus" which is listed at 170-180 days (mid-late). I seeded the first week of May (in flats) and had sprouts for sale a few weeks before Thanksgiving. The sprouts held great over the winter and I only just finished harvesting off these plants last week. Another variety like "Gustus" could be seeded the same time and be ready as early as september. I've never tried any early sprouts as they don't hold well and are prone to serious aphid damage where I live. That plus i'm still eating corn and tomatoes in Sept. and definitely not craving brussel sprouts! -Mark This post was edited by madroneb on Thu, Feb 28, 13 at 1:12

Have you ruled out the 'damping off' that seems to be a major seedling killer? (I've not had it myself, but description on the forum sound similar, and by moving them outside your starts might be more exposed to spores and such.)

They are pretty easy to grow, other than the typical cabbage family problems, animals and insects. Be sure to treat regularly for cabbage worms, and watch out for aphids as the sprouts are forming in the fall, as they can get into the developing sprout and make a mess. In PA, I'd say you can put out transplants any time between early April and about the first of July and still have success. Yes, there are different varieties, including purple ones, but you probably are only going to encounter a few very basic types at your local garden center, such as 'Long Island', 'Jade Cross' and possibly 'Bubbles' (I saw those this year). If you happen to have a more enlightened garden center, you might find something else. Folks in the West Coast might find different, overwintering strains from Europe.

I love Brussels Sprouts. My way of cooking: Prepare the B Sprouts. Peel them back a couple leaves, chop the bottoms off and chop them in half. Chop up some Onions, amount is per your taste. Cut Bacon into medium size squares. Steam the Sprouts for about 7-9 minutes. While they're steaming, start frying some Bacon that you cut into pieces. Take the Bacon out before fully done, but not raw. Fry Onions in the Bacon fat. Remove the Onions and throw the B Sprouts in a frying pan with a bit extra added oil if you used up all the Bacon fat already on the Onion. Salt and Pepper to taste the B Sprouts. Fry the sprouts until golden brown. Mix everything together and serve!