Rudbeckia can tolerate some shade and still bloom. Penstemon so bloom earlier and add great color. Some foliage plants like heucheras or coleus can also deal well with shade and add color all season.

Day lilies would do well there. They tolerate most light conditions and come in many colors. I have them in mostly shade to full sun. I like the reblooming ones.

Luxuriant Bleeding Heart does well in part shade to sun. It has fern like foliage and blooms with small pink flowers from first thing in the spring until fall. It does need to be watered though or it will stop blooming and fall apart

I would probably start by widening the bed by something like a foot so you have room for two rows of plants (plus maybe some edging plants) so you can fit in enough to get more flowers and more foliage interest.

Some other plants that work in part shade:

Pulmonaria - spring flowers and ornamental leaves with varying amounts of silver, depending on the type

Hosta - some are more sun tolerant than others

Hakone grass in the shadier parts

Jacob's Ladder

Heuchera (coral bells)

wild ginger

Astilbe if the area is moist enough

In the space between the hanging basket and the evergreen(?) shrub you may have space for one of the part shade clematis. They could grow up cords fastened to the deck rail.

I have to echo babs - my first thought was to widen the bed a little bit if possible.

Also, since it is near an entrance, I think I would add one more evergreen. It looks like you have something there by the corner of the deck, a chamaecyparis or juniper perhaps, but I think I would add something evergreen near the stair-rail, either in that corner or about where the monarda(?) is. Maybe a boxwood or small holly (ilex glabra compacta, Shamrock, etc.).

Any of the plants suggested above sound good, and of course I have to put in my plug for a nice variegated hosta! A hydrangea may do well there if there is room (I'm having a bit of trouble trying to gauge just how big this bed is) and if you don't mind the bare sticks in winter. And I love babs' idea of the clematis up the deck railing - that would be beautiful!

I too was going to suggest hostas and grasses. Here is a pic of my unknown hosta with hakonechloa aureola grass to give you an idea. These do get part sun....

Thanks again NHBabs for the ideas & tips. Sorry to say that I don't quite know what you mean with the V edge, etc. I'm clueless when it comes to landscaping, but I am learning a lot from this forum! I will also check my profile & add the zone. I should be able to figure that out without a problem! :-)

V edge is when you make two cuts that meet at the bottom so that in cross section they look like a V shaped space where you took out dirt and grass, perhaps 4" deep. Grass roots can't grow across air, so it stays on the lawn side instead of growing into the garden. It would need to be renewed every year, but probably not more frequently in zone 4's short growing season. Early spring would be good as soon as the soil thaws since you can't do much else until the soil dries out more.

There's a drawing in this Fine Gardening article, though the author's V actually has one vertical side. I am not fussy enough to ever 'hone the edge' in my big rural garden.

@NHBabs, wondering how I should go about the cords/trellis for clematis & when is best time to plant one of those?

My pleasure, Jaime. Just passing along the help others have given me.

Clematis climbs by wrapping leaf stems, so it needs something narrow to wrap around, such as a metal trellis with bars pencil thickness or less, or coated wire with 2" x 4" openings, or cotton string so you can compost it in the fall with the dead vines. With the string tie it to your railing, and anchor it to the ground near the base of the plant with stakes into the ground, or tie it around a brick at the base. You can fan them out toward the railing in future years as it gets larger, but that won't be needed the first year since they do more of their growing underground initially. I'd advise that you look for a type 3 prune clematis because they tend to be unfussy. At the end of the season after hard freeze, cut off the dead vines leaving a couple of buds per stem, and they will regrow in the spring. If you use string rather than a metal support, compost the string with the old vines and put out new string in the spring when the buds start swelling. All clematis take a bit of patience to get to full blooming size, usually 3 years to be good-sized, and after that they get better each year. I plant clematis either spring or early fall.