Can flower seeds be started directly in window boxes ?

Next Spring (zone 5a) I'd like to start seeds directly in window boxes but am unsure of the result. Since space is limited, starting seeds in flats won't work for me. I have 5 window boxes, 4 on my southeast facing deck and one under a west-facing window. When the one on the west side starts to look stressed from the sun, I replace it with one from the deck. French Marigolds that I started from seeds are in one with some purchased white Verbena plants. And combinations of purchased white and pink Alyssums with red, white and purple Verbenas in 3 others. The last one has Victoria Salvia (blue and white) and Gazanias, all started from seed, only about 6" tall now but they seem healthy. In February I started several flats of Coreopsis, Gaillardia, Gazanias, Salvia and Marigolds (among others that did not make it) and what a fiasco !!! It became so overwhelming that in April I began to plant them anywhere outside and in some of my pots and window boxes. So to avoid that situation again, if I direct sow Alyssum/Marigold/Gazania seeds in large containers, what will result? Also, my outdoor planting area is limited - heavy clay soil and a lot of rock and shale. I've dug through it in several areas and amended it but don't plan to dig anymore.

Yes you can plant your seeds in window boxes. Just be sure to plant for your zone.

The disadvantage of starting them directly in the windowbox is that you can't start them early as you could if you did them indoors in flats, you'll have to wait until the right time relative to your last frost date, and that means you won't have flowers as soon as you could if you started them indoors.

Yes you difinitely can, the advantage however, is that you don't have to harden them off..

"eyes"

I don't think I was very clear on my intent. I want to start the seeds directly in the window boxes INDOORS, the same way one would start flats, 6 weeks before last frost date or whatever the specific plant required. I wasn't sure if the root system would be too bound up to produce flowers all summer. There would be 2 or 3 different types of seeds started per windowbox, for example white Sweet Allysum and Celosia which both seem to like the same soil/sun conditions, plus a trailing plant which I have yet to discover. I bought Verbena plants this year and, with all the rain we've had in New York, it developed awful powdery mildew so I would not use that again. I guess my question is about the root system and length of time the plants will be growing in a container. Anyway, it's probably a silly question. I'll just have to try it and see. I'll also try the "winter gardening" technique - just discovered that and it seems an interestng challenge. Thanks for your responses to my post!