What are your goals?

Not much room for trees, shrubs will just eat up space.

Annuals but require maintance.

Your garden is just the soil/barked area? Sorry but too tight a space for a Japanese maple. Even the low grafted dwarfs spread quite widely and would need frequent pruning to keep in check. And that is never advised.

I'd just stick to modestly sized shrubs. You don't disclose your location but if appropriate, Sky Pencil Japanese holly could provide a vertical accent.

zone?

Please,

Don't plant a tree that has to be hacked off when it grows to large over the sidewalk or road.

a low row of day lillies or something evergreen to accent the walkway.

You can get the lovely color in a ninebark, a sand cherry or a weigela (you need the right cultivar, but they often have "wine" in the name. They are all shrubs and will fit the space better.

Will you add a photo from a farther out = so we can see the entire front of your house/townhome/semi detached?

Agree that you don’t have enough room for a tree as it will encroach in your driveway or neighbor’s yard. Plant a mix of small shrubs, bulbs, perennials and annuals.

Bonsai - Chinese Elm Bonsai Tree from EasternLeaf.com ; Characterized by its leaf shape and strong stem development, the Chinese Elm Bonsai tree will continually produce fresh leaves to any shape. This Bonsai tree is one of the most popular Bonsai tr

Thuja Occidentalis 'smaragd'

By definition, a bonsai is a miniaturized tree grown in a container. They cannot be planted in the ground. And to maintain the arborvitaes in that spiraled form will take constant pruning attention.

Neither are good choices for this situation..

And neither is a ninebark; even the smaller ones are likely to overgrow the widest spot you have. Hacking back a ninebark makes it look awful too.

BTW, your picture shows a young tree in the hell strip, likely planted by the city. The volcano mulch around the trunk needs to be removed ASAP. Mulch against a trunk means a dead tree in a few years. Hopefully it has been properly planted with the root flare showing. But often they are not.

I would plant perennials--day lilies, astilbe, nepeta, geranium.

Even a Dwarf Japanese maple will get too big for that small area…with cars so close best to plant perennials like August moon Hosta or lavender…looks like this area would get full sun.

In a container but outside. The idea behind a bonsai can adapt to a planter in the OPs space successfully as has been continuing in Japan for hundreds of years. Luckily, Japanese gardeners have not given any weight to random opinions. Container growing an ornamental tree gives you more control over its growth and shape. The garden here uses aluminum wire to shape the branch growth. This makes more options possible. Like a Japanese Black Pine as shown in the video for sale at $1M. Care is necessary for anything you want to grow here. Pruning twice a season for some like the arborvitae with watering and feeding. It's up to the OP, not me to choose.

I don't think anyone doubts that bonsai are amazing and that the Japanese have perfected the art over centuries. But they require a lot of skill and a lot of time. A specimen big enough to make any impact in the OP's space would be extremely expensive and would very likely be stolen in short order. Bonsai on a table in the back yard; lovely. In the front; a poor choice. The language of the OP's post implies limited gardening knowledge, so even the spiral topiaries would be a challenge to maintain. Small shrubs and perennials would be a much better choice. If height is required a couple of obelisks with Clematis could work.

Your comments would indicate you have not grown either the bonsai or the topiarized arbs personally. These are NOT plants for a beginning gardener, requiring a higher degree of attention and care than the average gardener possesses

As I mentioned, a bonsai is an example of the option of container growing a ornamental tree or shrub in the limited space available. Many different options requiring different levels of care and experience can be successful within this range of options. It's likely the choices available are already growing in a container. The nursery can offer advice on care to continue. Even a inexperienced gardener can learn. I've been growing my acer palmatum tsuma gaki in a container for years. It's not difficult and because it's relatively easy and very rewarding, I stand by my recommendation because of the enjoyment I experience during the season. Shindeshojo is in the ground but not as prized. Once the container option is on the table, I suggest a visit to your local nurseries to talk to people who will be happy to help you choose and set this up.

LOL!! Growing an Acer palmatum in a container is a world apart from growing bonsai. And it is not all that simple and straightforward either. The care required for a containerized tree is far beyond that required of an inground planting....of which I am fully aware as my entire collection of JM's (heck, my entire garden!!) is grown in containers. And they take a LOT of work!

Also, the risk of theft is still very much present.

@gardengal48 (PNW Z8/9) - I would love to see your garden + understand the work involved to have trees planted in containers. I was thinking about adding a few to my backyard - I have large trees - but I wanted to add some smaller ones by my patio.

Suggest adding a rock or two, a low growing evergreen, a hosta or two if room, plus a few annuals suitable in your growing zone/amount of sun/shade. This will result in a garden that isn’t empty over the winter and is low maintenance. Walk around your neighbourhood and see what others have done as well.

Hostas are easy and great fillers and need only to be split when they get too big. See below if suitable re: the conditions. I’d head to a nursery though with your picture and you’ll get great advice. Go when not busy and ask for the person that can best help you. They are happy to do so, knowing you’ll be buying from them.

For some unknown reason bonsai is the only option discussed. It's only an example of the many options open when a built-up planting box or other creative addition is placed on the space to accept a container grown tree or bush that otherwise would outgrow the space. A small Japanese maple of your choice could be grown in the space. Yes, it will take care. More than if it was just planted. In 3-4 years remove it from the container, replace some soil and trim the roots. Meantime keep it watered and fed. Anchor it against theft if necessary.

So pretty, Maureen! As long as there are no deer around--they love the hosta salad bar!

Container plants may walk away.

Not knowing the OP's climate it's hard to say whether large container plants would overwinter outdoors. Maureen's concept is the most workable so far.

Conversely, in a hot climate containers will need constant watering.