That sounds like it's pretty narrow for too many plants. What have you been planting in it? Does it stay fairly moist? Maybe with too many plants, they would battle for water. This coming from someone who has little luck with container gardening.

If it ends up working, I'll post pics after some growth. It could end up being a mess or really cool.

Oops, sorry Schoolhouse, I didn't see your post. I'm really just sticking leftovers in there. Mostly geraniums. I stuck the box on the porch railing under an ivy geranium. All the deck plants get watered each morning in the summer, so water shouldn't be a problem. But I do wonder about space. I suppose I could pull some out if they get too big. I want to shove one more in there. lol

I used to do window boxes, treating them like annual hanging baskets I'd really stuff them, keep them well watered and fertilized regularly.
My window boxes were in morning sun afternoon shade. I had purple wave petunias or other single flowering(nip back when they get scraggly), impatiens, pale blue and white lobelias (not the trailing type, these draped nicely over the edges, the trailing type got to be a bit much), lemon colored (Tagetes) marigolds, maybe some dwarf snaps, a couple of pieces of trailing nepta maybe an ivy geranium or whatever else struck my fancy at the time. The thing is to stuff them for visual impact :).

We once did 2 big moss hanging baskets with about 150 plants in each one. It took two of us to lift them into position as they weighed over 60 pounds. I wish I had taken pictures, to expensive to make now, it was back when you could buy flats of plants quite reasonably. Other nice plants for window boxes are Schizanthus and Salpaglosis.

Annette

Oh wow, Annette, everything sounds amazing!! I love the sounds of the moss garden. We're growing some moss on the north side of the house (didn't plant it), and I just love it.

The first one you mentioned sounds like what I've just stuffed together. Plus it's got 2 clems below it that have just reached the bottom of the box. It could work, or it could look ridonk. Sometimes the leftovers planters end up the prettiest.

Well if it works for you guys, I should give it a try, using smaller transplants crowded together. I might make a trip to the greenhouse tomorrow.

I have two window boxes. Each about 24" x 6". In each I have two geraniums, three baltic ivy, two vinca vines, two bacopa, and one verbena.