RoseBlush1 said:

@CaliFlowers, Ken ... Are you saying I should not put a layer of gravel between the clay at the base of the bed and the amended soil ? It would be next to the block wall.

I'm not Ken but gravel at the base of a planter under finer soil actually impedes drainage of the top layer. This is because water doesn't cross the interface between finer material overlaying coarse material until the upper layer is saturated. So it has the opposite effect of what one would intuitively think. Sooo, based on that, it would make the planting soil hold more water. This phenomenon is called a "perched water table".

Thank you, Sue. The reason I was asking about the gravel was because I was afraid I had forgotten something.

That bed will never drain down deeply. I did forget that soil next to a foundation, especially for buildings located on a slope, are mechanically compressed to a 98% density to provide stability for the the foundation.

I had planned to add a LOT of perlite to the amended soil to lighten the soil and will do some research to find out what the ratio should be when I back fill the bed to create the "perched water table" you mention in your post.

I do plan to put sheet metal between the soil and the wall so that there is no chance of moisture wicking up the stucco.

After more thinking, I've decided to use that bed as a "working bed" to start new plugs to allow them to grow larger root masses before being transplanted out into other parts of the garden and to test plants for heat tolerance. I won't be planting anything that needs deep watering.

To make it more attractive, I'll probably add some big rocks and possibly create enough shade for some other plants. Of course, I'll be testing those plants, too to see how they deal with reflected heat or heat absorbed by the rocks that might cause problems for those plants.

I'll use the gravel to repair the paths next to the sidewalks that have sunk due to subsidence caused by the drought. That will be gravel on top of gravel.

Thanks so much for the information you provided in your post. I feel comfortable going forward, now.

Smiles,
Lyn

Oh, Sue, I said it wrong. I have to find out how to lighten the amended soil so that I don't make a "perched water table" that makes the soil in the upper part of the bed too moist. Opps !

As long as you don't have layers with a fine-textured layer on top of a coarser layer you only really need the fill soil to be acceptable to the plants you want to grow, be well mixed and the same texture throughout the bed. It's layers that create the perched water table, which isn't what you want in that situation.

Thanks for stepping in with that information Sue, I was away from the forums for a while.

Lyn, I have a couple of articles which explain in detail what's going on with drainage, clay and also perched water tables. If you'd like, send me a tree mail and I can email them to you.

Ken

Thanks, Sue. I guess that means I have to excavate the rest of the soil that is still in the bed, about three wheel barrows worth so I get the whole bed down to the densely compacted soil around the foundation. That will leave me with two layers. Since I am planning to put plants that only need shallow watering in the bed and the compacted soil is down about two feet, I shouldn't have a problem.

Ken, I am interested and will send you a t-mail. Thank you.

Smiles,
Lyn

RoseBlush1 said:Thanks, Sue. I guess that means I have to excavate the rest of the soil that is still in the bed, about three wheel barrows worth so I get the whole bed down to the densely compacted soil around the foundation. That will leave me with two layers. Since I am planning to put plants that only need shallow watering in the bed and the compacted soil is down about two feet, I shouldn't have a problem.

Layers the way you'll have them wouldn't have the same effect as the perched water table because you will have coarser material over finer rather than finer over coarser. It's the latter that causes the perched water table. It's hard to say whether you need to go down as much as two feet. What happens if you pour water on it now that you've got partly there? Does it take a long time to soak in and puddle on the surface?

What plants have you tried there that didn't make it?

You seem better off breaking them down since there are huge cracks in the retaining walls. Demolish it and start over with a clean slate AND drainage holes

Hi Sue ...

Maybe I won't have to excavate all of the rest of the soil out of that bed. For me, that's hard labor because my back goes into full protest mode when I do that kind of work.

They clay soil in that bed was probably imported to the property when the J's imported soil for the front of the house. It is not the native soil on the house pad level in back of the house, which is densely compressed rock with clay and silt between the rocks. it is just clay soil.

Initially, I planted several micro-mini roses in that bed. I had potted them up to grow larger root masses before planting, so they were not just little bands. Those roses died because of both the intense heat of summer and poor drainage. I think the drainage was the primary culprit. I have other micro-mini roses planted out in the beds I've created on the house pad level that get the intense heat that have done just fine, but they have better air circulation and don't have the reflected heat from the wall as well as perfect drainage from the rocky soil under them. When I watered the roses in the bed, it appeared that the water soaked in just fine. However, when I pulled the dead plants, I found that they had root rot.

Then I decided to try sedums and hens and chicks since they needed less water. Unknowingly, that's when I created a perched bed because I went down about 10" and added a lot of decomposed granite and gravel to the soil on top of the clay soil that was in the bed. More dead plants. Again when I pulled them, I saw signs of root rot. They also fried.

I gave up planting in the bed and used large containers using xerotic plants on top of the bed. It was hard to keep any kind of moisture in the containers over the summer months because of the heat. So, to me, that was a temporary solution, because I have to winter protect the containers. I think the plants were hardy enough, it's just that the cold temps of winter were hard on the containers.

This time, I decided to excavate the bed and find out why it wasn't draining like the other beds. What I thought was going to be a simple project quickly became more of a problem project.

I am thinking in layers again ... not true layers, but lightening the soil in the bed as I go up. The denser clay amended as needed for about a foot and then soil that is even lighter and amended with organics and perlite nearer to the top of the bed. What is the best way to implement that kind of thing ?

Lyn

Hi Lee-Roy ...

Arico said:You seem better off breaking them down since there are huge cracks in the retaining walls. Demolish it and start over with a clean slate AND drainage holes

That would be an ideal solution if I were younger. To be honest, I'd rather leave the bed empty and just cover the top with interesting rocks than to take on that kind of labor

Lyn

RoseBlush1 said:

I am thinking in layers again ... not true layers, but lightening the soil in the bed as I go up. The denser clay amended as needed for about a foot and then soil that is even lighter and amended with organics and perlite nearer to the top of the bed. What is the best way to implement that kind of thing ?

I would try and keep the replacement soil equally mixed throughout to be on the safe side.

OK ... I'll start digging the other soil out ... I don't have to do it all in one day

Smiles,
Lyn

Have you thought about filling the bed completely with gravel? (road grade gravel that has a bit of sand in the mix). I was amazed at the health of plants at a local nursery growing in gravel beds, with no soil whatsoever, and they never needed watering. The plants just extend their roots however deep they need to go.

RoseBlush1 said: ...
I am thinking in layers again ... not true layers, but lightening the soil in the bed as I go up. The denser clay amended as needed for about a foot and then soil that is even lighter and amended with organics and perlite nearer to the top of the bed. What is the best way to implement that kind of thing ?
Lyn

I figure that clay and silt are going to sift down out of the upper layers and accumulate in the lower layers over the years, so I wouldn't deliberately start the bed that way. I would try to make the soil uniform.

However, anytime that isn't practical, I BLEND the soil in the transition zone between tow layers. Usually just by messing it up a little with a shovel and a cultivator. If the transition is gradual, I don't expect to get much perching.

In your case, it doesn't sound deep enough for much layering OR blending.

I saw this thread late, and you've probably already made you decision. But here's what I typed up before I got that far in the thread:

First, there's the principle of "if you can't extend the root zone DOWN, build it up. That's what the containers sitting on top did, gave you free-draining root zone ABOVE the clay.

If you accept that the bed will never have well-draining soil much deeper than the grade of the soil outside the bed, you HAVE to build it up or grow only shallow-rooted plants. Maybe use boards wedged between bricks and soil to imitate taller walls and support more soil.

This next idea would be expensive or a LOT of work, so not practical: If someone offers free bricks, add a few rows of brick on top (with or without mortar). If you have rocks that can be stacked neatly to make the walls a little taller, there you go.


It sounds like draining STRAIGHT DOWN will never work. How about draining "mostly sideways"? Like an almost-horizontal French Drain that runs at a shallow angle from the bottom of your bed to a lower spot ... or at least a long enough trench that, after it fills up, water CAN perk down out of it fast enough to provide a basin for your bed to empty into.

(One bed I have drains into a nearby hole that's large enough to hold most of one rainstorm's worth of water from that whole bed. The hole usually drains mostly empty between rainstorms during the growing season. Your "horizontal French Drain" would be like my drainage hole - a holding zone for runoff, a little deeper than the bottom of the root zone you're creating.)


However much you dig the bed down INSIDE the brick wall and amend it, you should probably also dig down and amend the soil surrounding the OUTside of the brick wall to the same or slightly deeper depth.

Then, assuming the brick has some cracks, or you drill some holes, or the amended soil extends lower than the bottom of the bricks, water inside the bed will wick through and under the brick wall. In effect, it would drain "sideways" into the soil outside the bed.

Now you have to make sure that the soil outside the bed has some channel or trench to carry excess water away from the bed. That channel might need to be mostly below grade, hence I suggest just digging amending a trench rather than your whole backyard.

The hard clay "floor" of the bed should slope down a little as it gets farther from the house, to encourage drainage away form the house.

The amended soil on the outside of the brick wall can be narrow, if it connects to a trench that continues the downward trend away form the house. I make these mini-drainage trenches barely wider than my mattock blade, and that seems enough to handle a medium amount of rain. Back fill the trench with very amended soil that drains adequately (or some people would fill it with drainage garvel".

The bricks may stay more stable if you don’t undermine the entire wall with amended soil. I would amend everything inside the bed, plus a strip outside the bed, but only undermine around 30-50% of the wall. leave 50-70% of that hard, hard clay in place to support the wall. Just tunnel under a few places in the wall (short trenches) to let water out of the bed. A shovel's-width ought to be enough for each "mini=tunnel".

Amending those tiny tunnels with organic matter that wicks is extra important. Bark, compost, grit and coarse sand are what I would use. Coir if you have it.

Hi Rick ....

Thanks for adding so much information to this thread.

I went out and measured the depth inside the bed and outside of the brick. The height from the soil to the top of the lip of the brick is 9". The depth inside the bed is 20".

No, I am not going to mess with the soil outside of the bed. That is the native house pad soil of tightly compressed rocks and clay/silt. It drains perfectly. Even when the gutters over flow because of a hard rain, there are no puddles. It doesn't make sense to mess with it.

"Going up" doesn't seem like a viable option in this situation because I would end up with moist soil next to the stucco. Yes, I could also extend the sheet metal barrier up, but I really don't want to go there this fall.

Now that I know I can't really fix the drainage problem in that bed, I'll just amend the soil as uniformly as possible and plant shallow rooted, heat tolerant plants there. As I said above, I may just use the bed as a working bed to grow larger root masses for plants that will be transplanted to other parts of the garden. Instead of potting up plants to grow roots, I can use that bed.

@JuneOntario, June ... planting in gravel is an option. I am using that method down in one of the street beds. I just don't think I have it in me to haul up the amount of gravel I would need for that bed from the street level up to the house pad level. Thanks for the suggestion.

Thank you to all for the suggestions and the information you have provided. Now that I understand the concept of a perched water table and know that the bed will never drain properly I think I can go forward with amending the soil for the whole bed and will understand how to use the bed. If everything dies, I can always just put the decorative rocks there. I have rocks of all sizes and could make something look interesting.

Smiles,
Lyn

>> plant shallow rooted, heat tolerant plants there.

That's smart - use it for what it is, instead of working hard to try to make it something it isn't.

>> the soil outside of the bed. That is the native house pad soil of tightly compressed rocks and clay/silt. It drains perfectly.

I had forgotten, or didn't understand, that even the compressed soil drains well, straight down. I thought it was impervious, to throw water away from the foundation. You have no need at all for a "horizontal French Drain".

Thanks, Rick.

Trust me, I didn't understand the dynamics of the soil in this garden, but continue to learn as I go along.

Smiles,
Lyn

You have the strangest "soil" I ever heard of. Hardpan or caliche might be harder to improve, but your rock/gravel/clay setup was a new one to me.