You're on the right track by removing the rocks and rubble, and amending the soil.

Consider getting your soil tested so you know what should be added. Your local government agricultural extension office should be able to help. Clay plus sand, well mixed, is probably a good start. Maybe you need more organic matter such as composted manure.

https://nicksgardencenter.com/gardening-blog/plants/shade-loving-plants-and-shrubs/

https://www.denverpost.com/2017/06/23/growing-gardens-in-dry-shade/

https://planttalk.colostate.edu/topics/design/1108-shade-garden-perennials/

here are pictures of similar houses to give you some visuals.

I like this one with the flower beds.

Ignore the shingles on this, but just look at the way they did the little gathering area. flower beds, stepping stone, hardscape for under the table, plants on either side of the window.

btw, if you have ever wondered what your brick would look like painted (Romabio) :

I really like this black one w/the wood accents.

this home is set up like yours. they did some raised beds on either side of the front porch area

Do not add sand to clay. Add organic matter to amend the soil.

https://extension.oregonstate.edu/news/theres-no-break-people-who-garden-clay#:~:text=The%20best%20way%20to%20improve,used%20to%20improve%20clay%20soil.

The linked article strongly supports the advice to add organic matter to clay, not sand.

Textural modification of small planting areas tends to produce problems with how water enters and exists the amended area. Particularly for long term types like shrubs it is recommended to select kinds suited to existing soil conditions and plant in loosened existing soil, without amendments.

Where a body is determined to grow kinds that seem to need a different soil than what is already present the most direct approach is to excavate the existing soil and replace with different, more suitable soil. When this is done the excavated area has to be wide enough that installed plants do not soon encounter the interface between the added soil and the unmodified soil around the edges of the excavation.

I spent two years getting the rock "mulch" out of a flower bed so I could have all day lilies. Well worth it.

I was think you need some height, especially since the windows on the right side are shorter than the windows on the left. I think the pic Beth posted with the raised, timber clad planter boxes could really enhance the entrance. You have a very cute house!

Wow, thank you everyone for the great ideas! Beth H., your photos especially gave me some ideas I have not considering before. I particularly like the idea of adding a cedar screen or trellis in front of the window on the right. It would also break up expanse of red brick and add privacy to our bedroom that looks out to the street. I have also thought about putting a smoke tree, serviceberry, or something similar there for more privacy in the summer when we like to keep the windows open.

But now, back to the issue of the existing rock garden! To be clear, this foundation bed is built up about 12 inches. It is 18 feet long and six feet deep, with 24” of the depth cover red by the overhang and gutter. We recently removed the pavers that we thought were holding in the sides of the bed but the “soil” has not budged an inch. I am not sure it would be possible to rehab the soil for regular foundation plantings. It would likely require removing the 12 inches of rocks, clay, sand, and rubble, and then planting in the soil below it (after amending).

I have absolutely no idea what we would do with the material we remove, and it would be a big job. Any ideas about that?

Before we go that route, I am curious as to if y’all think the existing bed would look silly planted up as a rock garden. If we did not have mature trees in the front, I would have already removed the weed fabric, mulch, buried the boulders partially, and planted it up. But given the trees, I am not sure if it would work aesthetically.

Are there any rock garden plants that get any kind of height? Maybe dwarf conifers? What would work for edging? And how could we blend all the panting areas and hardscaping together better?

This area is considered part-sun here in Colorado, but gets very hot up against the brick and this area gets some direct sun mid-day (except under the overhang).

Am I correct that the built-up portion is rocks, clay, sand and rubble at a depth of 12", and underneath that is clay? You describe the area as "fast draining". Of those things, only sand is fast draining so I am trying to understand what you have. Clay is very slow draining.

My parents live in a clay area and built up a garden with purchased topsoil. Anything with fairly shallow roots (beans, lettuce, cucumbers, perennial flowers etc.) does very well. But anything with deeper roots e.g. raspberry shrubs, died when the roots reached the clay under the topsoil. Raspberries don't like wet roots and the "bathtup effect" of well-drained soil over clay.

Shrubs planted in the unamended clay (yews, junipers, mulberries) grow just fine. Their city (Welland, Ontario) is know as the Rose City because roses really love clay. It holds moisture well and is high in minerals.

If it was my house I would run a porch all across the front

@partim, that is correct, there are about 12 inches of rocks, sand, clay, and rubble built up on top of alkaline clay. We have some junipers planted in only slightly amended clay in the hottest part of the backyard that are pretty happy. I did not know roses loved clay! Maybe some of those low groundcover types would be nice...

Just google a list of plants for eastern exposure and find some for your zone. Be sure to not plant them too close to the house.

It sounds like the plants you moved were not thriving due to lack of sun rather than rocky soil.

The Denver Botanic Gardens has one of the premier alpine and rock garden collections in the world - and it's in your backyard! I would strongly suggest a visit to get some inspiration and plant suggestions for your area.

Okay, I have decided to dig the rocks out of the bed and then see what I am left with! Right now, because I am inpatient and the respective manual labor is therapeutic, I am chipping away at the edges of the bed with a pitchfork and raking off the top layers of rocks.

What are my options for separating the rocks and clay soil? And if I get tired of chipping away at the edges of the bed, what are my other options for breaking up the bed?

Can you give us a close up photo of the bed? in your first post I see some large rocks, and a few that are baseball-size. Are those the rocks that you are removing?

I am concerned that you may be doing a lot of work for relatively little benefit. If the rocks are small, shrub roots will find their way around them just fine. In nature, rocky soil is not a barren wasteland. You just need to figure out what to plant in it.

I would put a piece of plywood down on the lawn and toss the soil there as you dig. Then you can poke through it. I've done this before and it is a dirty job but not really hard. I also used a pickaxe but it was a small one.

When you are finished soil can go back and toss some compost on top.

BTW, I never had difficulty growing plants in my rocky area. It was just difficult to dig the holes for the new plants.

@partim Thank you for your concern! Here are some closeups of the bed this morning. There are some larger rocks, but also tons of gravel as the pictures show. Most of the bed has

@emmarene9 Wow, you picked through the entire bed by hand? You have more patience than me! 😊

How small were the rocks in the ground you planted shrubs?

I used an old deep fry strainer basket to sift the rocks out.

It was mostly between gravel and river rock size. Occasionally a larger rock and I found a few volley ball size rocks buried completely. Nothing as large as your big rocks though.

Add a bit of color with and artificial living wall, it has no maintenance and looks incredible on brick.

Upscapers

I would take these pics to a local garden center and get their advice. https://www.gardeningchannel.com/plants-that-grow-in-rocky-soil/

There are some wonderful plants on this list. Thanks, @partim!