Striking architecture. Decades-old planter boxes should be emptied of their depleted soil, then refilled with good planting mix. Check drainage while you are at it.

This spring I would plant blooming annuals. If they do well, then you get enough sun for many types of native plants. If they don't do well, you'll know the box needs shade plants. If you already know what the exposure is, head over to the local nursery to ask about perennials or native plants.

What in goodness name is root weed? Hakone grass might grow there, I don’t know if stephanandra would be too much/need more light.

I would get architectural plants like Sedum.

J Williams I had never heard of it either. I looked it up. One name is Polygonum cuspidatum

and it sounds like a pest.

Mydogmiddy, your planter is very long. I think you could have a few types of plants. I don't know what grows in your zone but I would look for some prostrate shrubs and a few perennials.

Cool house and cool planter.

That is absolutely crying out for some Weeping Blue Atlas Cedars. It prefers full sun, but I see it growing on some very shady little streets around Rittenhouse Square in Philly. Train some of them upright, the rest trailing.

Thank you, thank you for your suggestions. Japanese root weed is an invasive plant that ruins concrete and spreads fiercely. All the riverbanks around my town are overtaken by it. We used some really strong stuff to kill it. I think the main problems is that the soil needs to be replaced and before we try to grow anything else. We added soil but everything died. This area gets full sun!

Thank you also for the nice comments about the house. The architect was a FLW apprentice.

How tall is the planter box? Hard to tell from the picture but it looks to tall for any perennials to survive the PA winters. The roots will freeze.

If you added soil without replacing it and used a strong weed killer you may have residual herbicide in the soil. If the roots of the invasive remain they could also act as a reservoir of the herbicide. Replacing all soil may be a better option but definitely choose a soil that is designed for containers. Soaker hose or drip irrigation is a good idea. But definitely check how well this drains. To remain moisture use decorative mulch. Pine bark would potentially work well And retains its color well.

I would probably start with the other homes in your neighborhood to see what plants do well in the area especially those that may have a similar planter box.

However, while you're getting ideas use annuals to add some color and life. They are cheap and it won't matter if they don't overwinter very well.

Also while native plants are a good option you will still need to determine the best type of plant for your dry sunny condition. Also this isn't a native soil or native conditions so I'm not sure that a native plant is the only or ideal choice.

One place you could also get some information is from your master gardener extension website. Is there a local botanic garden you could use for information on what does best in your region? In Chicagoland I tend to use the U of I extension, Morton Arboretum, & Chicago Botanic Garden for ideas. But I also ultimately joined some gardening groups and speak to folks at local nurseries for ideas. They often have a very good idea of what works best for your area. Take pictures and have some idea about light (full sun, partial sun) so you can give them enough information to help. Having the dimension (LWH) of the planter will help. Also identify how much time you realistically have to maintain the plants in the container. Some plants may require more care than others in terms of pinching back to promote an ideal growth pattern, deadheading spent blooms, and the like.

My experience with soaker hoses has been they were fine for a couple of years but eventually clogged from the hard water in my area. I am now switching to drip irrigation to see if that works better.

OK. I think you are talking about Japanese knotweed. Make sure you’ve totally eradicated it before planting anything.

Given the Pennsylvania winters, you could use annuals in one part of the box and try some perennials in another part. If the perennials don't survive, then replant with annuals every year. When winter comes, enjoy the sculptural effect of the box by itself with occasional snow. Or see what a place like Winterthur does https://www.winterthur.org/ 

What are your thought on a spreading cotoneaster?