Question Concrete Block Planter Beds

[Lisaceae]

Here in Southern California, have two tiers of mortared concrete block retaining walls with footers built about 15 years ago. They are only two foot high, with what looks like loamy soil behind them and soil beds that are three foot wide. Upper tier has a slight slope upwards connecting to back neighbor's yard. The tiers are about 53 feet long but divided by some steps into two 30 foot long beds and two 20 foot long beds.

The original goal was to put plants in them and irrigate (Irrigation lines were dug in about 6 years ago). However they were never planted. So walls still look good with a little mortar missing and a little efflorescence.

Soil was dug out to see what the drainage system was like. There was a 3 inch french drain pipe sitting on top of the footer with no slope or wrong slope. However there was gravel and fabric around it with what looked like a thin hot mop type of paint on back of walls as well as a plastic covering it. Pipe ran under steps to connect both sides of tiers and only one outlet at one end, so pretty long run. Pipe from upper tier connected to lower tier pipe at the outlet site.

Now that we are retired and have the time we want to plant fruiting and flowering trees, shrubs, perennials and annuals. As this is southern California, we get on average about 16 inches of rain a year. The irrigation plan is to have drip irrigation, with occasional deep watering with hose as needed. There is no groundwater here as it is inland from the coast about 15 miles.

However the plantings and their root systems seem at cross purposes with the principles of longevity and integrity of the concrete block walls. The plants will need a decent soil depth, preferably 18 inches or more, from one -three feet of width depending on plant type, and a soil type and watering scheme that will provide good drainage but also good water retention in the soil. I wish the walls were taller and wider, but this is what I have to work with right now.

Trying to reach a compromise in my head, I have toyed with containerizing the trees, and choosing other plants with non-invasive roots, and various modifications of soil texture to get the right moisture (need help with this), as well as different drainage techniques. But this is a little above my head as the science and logic is complex or even lacking out there, especially in this very site-specific situation.

I will be re-waterproofing the back of the walls also with accompanying protective membrane. If french drain pipe not needed, then how should I proceed? If needed, then need to know gravel amounts, placement, etc.

There are so many variables so going a little nuts. Any ideas and help to how to make this all work together or strategize would be greatly appreciated.

 

[ClissAT]

Hi Lisa , welcome.
As the saying goes, a photo is worth a 1000 words.
So give us one of your terrace walls and one of the general area of the state showing the natural land with its natural growth so I can get an idea of soil type.
You being in California and many of us here being in Australia, it can be hard to give the sort of exact advice you probably need.

But no matter where we are in the world there are certain geological physics that apply worldwide.
Water always runs downhill, ie gravity.
Water is pushed around by pressure from above, either soil pressure or depth of water.
No amount of soil improvement will hold water in soil if there is enough pressure and gravity being applied.
Sometimes it's better to do nothing than bash your head against said wall!

Maybe find local (indigenous) cascading landscaping plants that will tolerate the soil the way it is now and save yourself a lot of money, water, effort and time.

 

[Lisaceae]

Here are some pics. Soil is pretty much a loam type I think and it drains 1-2 inches per hour according to our perc test. Climate here in southern California is similar to some parts of your Australia. Eucalyptus, Bottlebrush, Tea tree all do well here. Many South African plants also do well here, and of course, Mediterranean plants. However, I have drought tolerant and indigenous plants in the front of the house, but in the back where the walls are I want to plant fruits and vegetables behind the walls. But I can try to be careful as I said above, e.g., containerizing any aggressive fruit trees. Really need to know if I need a french drain or similar or if its Ok with just waterproofing (Sika 320NS) the back of the wall and using a dimpled drain board. You can see the black waterproof coating in picture below and also where the old french drain was (above the footing which I think is weird but I am no expert). Also picture showing the fence where neighbors yards are a few inches above ours and picture showing our perc test hole. Since all the soil was dug out already we had to test at the footer level.

 

[ClissAT]

Thanks for those photos, its always good to know exactly what we are talking about.

So one of the things that happens with elevated narrow blocks of soil is that they dry out rapidly. Ref my comment about gravity and water.

Then there is the extra heating that occurs to these places due to this bit of soil having more external surfaces exposed to solar heating.

Many people have theories about improving the soil or making special mixes of soil to attempt to remediate these issues.
The proof is to be seen a couple of years later usually with the sight of unruly shrubs with one dominating species and cascading long grass!
Or, bare terraces that only receive the attention of the weed sprayer.
If you find one that is successful, call in, introduce yourself to the owner and pick their brain!

So I would say, the next challenge for you is to drive or walk around your suburb and find another terrace installation that is succeeding.
Pick the owner's brains and follow their advice.

Now if you don't find any successful terraces, that tells you not to try yourself.
Make different plans!

 

[Lisaceae]

Thanks for those photos, its always good to know exactly what we are talking about.

So one of the things that happens with elevated narrow blocks of soil is that they dry out rapidly. Ref my comment about gravity and water.

Then there is the extra heating that occurs to these places due to this bit of soil having more external surfaces exposed to solar heating.

Many people have theories about improving the soil or making special mixes of soil to attempt to remediate these issues.
The proof is to be seen a couple of years later usually with the sight of unruly shrubs with one dominating species and cascading long grass!
Or, bare terraces that only receive the attention of the weed sprayer.
If you find one that is successful, call in, introduce yourself to the owner and pick their brain!

So I would say, the next challenge for you is to drive or walk around your suburb and find another terrace installation that is succeeding.
Pick the owner's brains and follow their advice.

Now if you don't find any successful terraces, that tells you not to try yourself.
Make different plans!

Thanks for those photos, its always good to know exactly what we are talking about.

So one of the things that happens with elevated narrow blocks of soil is that they dry out rapidly. Ref my comment about gravity and water.

Then there is the extra heating that occurs to these places due to this bit of soil having more external surfaces exposed to solar heating.

Many people have theories about improving the soil or making special mixes of soil to attempt to remediate these issues.
The proof is to be seen a couple of years later usually with the sight of unruly shrubs with one dominating species and cascading long grass!
Or, bare terraces that only receive the attention of the weed sprayer.
If you find one that is successful, call in, introduce yourself to the owner and pick their brain!

So I would say, the next challenge for you is to drive or walk around your suburb and find another terrace installation that is succeeding.
Pick the owner's brains and follow their advice.

Now if you don't find any successful terraces, that tells you not to try yourself.
Make different plans!

Hi Lisa , welcome.
As the saying goes, a photo is worth a 1000 words.
So give us one of your terrace walls and one of the general area of the state showing the natural land with its natural growth so I can get an idea of soil type.
You being in California and many of us here being in Australia, it can be hard to give the sort of exact advice you probably need.

But no matter where we are in the world there are certain geological physics that apply worldwide.
Water always runs downhill, ie gravity.
Water is pushed around by pressure from above, either soil pressure or depth of water.
No amount of soil improvement will hold water in soil if there is enough pressure and gravity being applied.
Sometimes it's better to do nothing than bash your head against said wall!

Maybe find local (indigenous) cascading landscaping plants that will tolerate the soil the way it is now and save yourself a lot of money, water, effort and time.

 

[Lisaceae]

Thank you ClissAT
Good advice. However most people who grow fruits and vegetables, let alone fruits and vegetables in raised beds, do so in the back of the house and not in the front where I can see. Will keep looking. So for right now will keep my fingers crossed that the combination of a loam soil, waterproofing the back of the walls, putting up root barriers, using mostly drip irrigation, and the fact that these are relatively low walls and only three foot wide beds will be amenable to fruits and vegetable growing while not compromising the integrity of the walls. I am going to leach the soil really good before planting also to remove salt buildup which is frequent in our semi-dry area of the country. I am going to forego putting in a french drain in lieu of the waterproofing and dimple drain behind the walls as I think this will be unecessary with such short walls in a relatively dry climate. Still not sure of the soil amendments needed, or if, as you say, the beds will be too dry. Will probably put in some organics as everyone seems to feel this is a good idea. Do you?

 

[ClissAT]

I meant any sort of terraced setup growing any sort of plant.
If the setup doesn't look really new but the plants are doing well, that tells you you'll most likely be successful.
If its a mess or bare, then you know to expect lots of hard frustrating work.
Applying organic materials to any soil always improves it.
For how long and at what cost is another question entirely.