You would have to pay attention to the light requirements but I would put something taller back towards the corner, either branching or evergreen, something that will give you form throughout the seasons. There are a lot of perennials that work well draping or hanging over the edges of stones. You are going to have to pay attention to scale of plants and their form/shapes because of the small space but it could be a jewel of a garden space. I would look for small space garden books/articles (online or at public library) for ideas. If you are not familiar with plants in your climate I would contact your local University Extension Service. They usually have a wealth of information on tried and true advice for a given region.

Are you considering enlarging the bed or keeping it the same?

Just based on the pic and going by my idea of cottage garden .. Since you mentioned hostas I'm guessing it's fairly shaded mostly. I would stagger the hostas , mix in some beautiful fluffy astilbe for color.i had Lamium mixed into my shade garden and it was nicely spreading. Also a clematis would prob do well on the porch column , something bright like ville de Lyon or comptess de Bouchard. Those did well for me in a shaded area. Then I'd add a window box with impatiens and maybe a trailing vine or two . Also something in the empty corner , not sure what tho. Maybe a hydrangea ? I'm sure you'll get lots of great suggestions here ! Please update us in the spring :)

Thank you both so much, freezen and lily! It's not just the stone retaining wall that's the garden space. It's also the space in front of it that just looks like grass, if you hadn't already guessed. I'm definitely doing window boxes, hydrangea and maybe tall things in the back.

Hostas grow in the front part that just looks like my yard. If you already knew that was part of the garden space, apologies!

What a nice space for a garden. I like the rock wall. What kind of light does this area get? Dappled sun and shade all year like in the photo, or either more sun or more shade during the growing season? What is your soil like? I find it difficult to tell how large the area is, so a ballpark estimate would help to tell what there is space for.

I'd start with removing any non-garden plants growing here and then mulch (cardboard with cut-outs for the hosta with an organic mulch like chopped leaves or wood chips on top) and weed a lot the first year so that when you add plants your weeding and maintenance will be minimal.

Since this area will be visible as folks go in and out of the door, having plants with year-round interest and/or some ornament such as sculpture or a birdbath will be important in making this area appealing. I think I would try to plant mostly lower growing items in the front part of the garden, or at least airy plants so that the stone wall is a visible feature. If some of these are evergreen/gold/red, they will provide interest in the winter.

In the upper part behind the stone wall, if there is room I'd add background plants with year round interest such as a colored foliage evergreen, and /or variegated red-twigged dogwood, ones that would stand out well against the light walls. With any woody plants, check the ultimate size and be sure you have room to paint or do maintenance behind it if it isn't a plant like the dogwoods which don't mind being cut to the ground. If there is enough light, a pretty trellis with a clematis that gets cut back in the winter (type 3 pruning) would feature the clematis in the growing season and the trellis in the winter. I would probably put a row of low-growing or easily pruned evergreens such as one of the smaller boxwood varieties under the window to provide winter interest and then plant the rest of the area with perennials to give you more interest in the growing season. Particularly in a smaller garden such as this that is in such a prominent place, thinking about varying the foliage color and texture (as you are doing in thinking about adding coral bells) will help add interest to the garden when there aren't many blooms.

In addition to the library as a resource, Pennsylvania has public gardens that might give you inspiration, both for plants and for design.

Here is a link that might be useful: Pennsylvania public gardens

What I would do is remove the stone wall as it's very low anyhow so the soil could just be sloped. I'd use the stones as stepping stones throughout the bed as it's too wide a bed to garden without a path thru.

Choice of plants depends on your climate zone and level of light. Use low growing plants at front and side edges and tall plants at the back but otherwise intersperse various heights throughout the bed for interest.

Oh I am sorry I misunderstood the amount of space you had! That's great to have so much to work with ! Do you have any pics of the whole front of the house ? I ask because I don't want to give an overkill kinda suggestion. I agree with the above posters on a lot of points! If you don't already have a bird bath somewhere they can be very cottagey. Another thought is to move the large rocks that you can't use as stepping stones to the front as a border next to walkway. Perhaps use the flatter stones as a path in a route to the bath then window so you can water the boxes ? I think you definitely have plenty of room for some kind of focal point! It's a great space and would be very welcoming !

Your own ideas will trump my suggestions but the first thing that comes to my mind is to eliminate the linear look by switching to a curved edge to the bed(s) in the photos. Even slight changes from the straight edges would add interest.

Here's a question: what direction does this bed face? East/West/North/South would likely influence the replies you get. My own garden is oriented with the compass and faces due east. That lets me judge what plants will do well based on the hours of sun they receive taking into account shade from trees & the house roof.

Don't disqualify coral bells from your garden design--they can add color and form all season long, as do Stachys/lamb's ears 'Helen Von Stein' and variegated Japanese sedge grass. The sedge thrives in sun or shade; the Stachys prefers a bit more sun. I have both growing in several beds.

For late season interest at the back of the border, consider Cimicifuga racemosa/black snakeroot, Tricyrtis hirta/toad lily & Chelone/turtlehead. All perform well in full shade as well as part sun so long as they're planted in healthy soil.

Perennial geranium*, Hellebore/Lenten roses, Alchemilla mollis/lady's mantle also serve me well as low-growing edging plants in both full & part shade.

*NOT the annual Pelargoniums/geraniums you see in window boxes. Perennial geraniums are low-growing, mounding perennials with a season-long bloom period

Depending on sun exposure, you might want to plant some columbines, bleeding heart, Penstemon/beardtongue & Virginia bluebells for early-season interest.

Where I am, Dianthus is a fragrant early season bloomer that seems to thrive in whatever conditions it's planted.

Most of the plants referenced above are easily grown from seed for just the cost of potting mix & seeds.

Best of luck to you!

Sorry to be a bit of a wet blanket and I don't know how your house is constructed but I'd be a little bit concerned that the earth appears to be piled against your walls well above the damp proof course. The bed appears to be about a foot higher than ground level and it looks as if there are already rain splashes or even green algae growing on that right hand wall. And what happens to the water that comes down those three down pipes? Does it go into drains or is it going into the bed? I'd try to establish the potential effects on the house of the piled up bed before planning plantings.

Floral uk, you beat me to it!
After grading and drainage issues are taken care of I would arrange the rocks to look like rock outcroppings and add small conifers before considering perennials. Generally perennials make poor foundation plants.
Mike