blue_canApril 30, 2010

I'm remodelng my yard and am trying to create a suitable bed for planting a couple of dwarf fruit trees and some flowers. I live in Socal where we have clay soil and over 50% or more of the soil is large rocks and boulders. My plan is to excavate to around 2' deep and remove the soil and rocks and replace with amended topsoil.

Should I be adding topsoil to such a depth. I figured that the plants would be garanteed good soil as it grows by digging to such a depth. Is this the correct thing to do or are there are downsides to adding so much amended topsoil.

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jean001(z8aPortland, OR)

Lots of downsides to that plan.

But to be brief, it's best to work with existing soil. Amended clay provides a stellar root medium for annuals; mix in 2 inches each year you plant.
For perennials & woodies, plant in existing stuff, then apply an organic surface mulch, about 2 inches deep; top off as needed.

who gardened in LB, CA for 30-some years.

    Bookmark   April 30, 2010 at 5:22PM
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Thanks for the feedback Jean. I assume I would at least need to dig and remove the rocks and boulders. Given the density and sizes of the rocks I'm unclear how the root system could grow and expand in such an environment.

    Bookmark   April 30, 2010 at 6:08PM
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jean001(z8aPortland, OR)

Don't know the size or numer of what you're referring to.

But, other than being in your way, they won't be a problem. Planting in and among true boulders won't be the traditional garden bed, but could be both attractive and interesting

    Bookmark   May 1, 2010 at 1:23AM
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That would be a very expensive way to replace some of your soil and may well create for you a "bathtub" where the water will accumulate in the soil you put in and not be able to drain out and everything you plant could drown.
"Topsoil" is simply the top 4 inches of soil from some place, although I have found most people think they will be getting loam when they buy "topsoil". While I have seen some very good "topsoil" I have also seen stuff that was garbage and not even worth the cost of trucking it in. Look closely at what you are buying, before you pay for it, to be sure it is something close to what you really want.
Far better is to amend the soil you have with organic matte, which is what your soil needs, not replacement. Compost or any other form of vegetative waste, and if that is all that is available even peat moss would be, usually, a bette choice of material than "topsoil".

    Bookmark   May 1, 2010 at 7:37AM
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Yes, you're correct - I was equating topsoil with loam which is probably incorrect. I do have some existing plants in the yard planted by the previous owner and the bed on which they are growing is not native soil and all the boulders have been removed (to a depth of about 1'). I recently planted a pomegrante tree in that bed and I used a bag of topsoil (cannot remember the name of the manufacturer) but it did specifically say that it was loam. I mixed that with organic compost and planted in that.

I guess amending the soil sounds like the best solution although I will probably remove all the boulders.

btw my soil tester shows the native soil to be slightly alkaline so I'm not sure if that's a good thing also.

    Bookmark   May 1, 2010 at 10:52AM
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jean001(z8aPortland, OR)

A pH near neutral is the usual for SoCal. And that's fine for growing many plants. Then, too, mixing compost into the annual beds will help even more.

    Bookmark   May 1, 2010 at 11:45AM
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The average rainfall in southern California is less than 20 inches per year while just to the north in Oregon the average is in the 60 to 80 inches per year (some places get mush less while others get much more) so you do not get enough rain to wash what makes soils alkaline out of the soil so your soil tends to be alkaline. Sufficient quantities of organic matte should help with that too.

    Bookmark   May 2, 2010 at 7:43AM
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billums_ms_7b(Delta MS 8A)

Instead of digging down into your yard and replacing soil, why not build up a hill of new soil (a berm) on top of your clay and plant in that?

I would still go ahead and till in a lot of compost into your clay in the area where I intend to build the berm and plant.

    Bookmark   May 2, 2010 at 3:22PM
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You know the answer to the question "How do you eat an elephant?" ONE SPOONFULL AT A TIME. Same applies to most large scale gardening projects.
OVER TIME, given enough organic matter, that clay soil will morph into the richest soil you can imagine.
OVER TIME, you can excavate the manageable-sized rocks and build around the boulders. Those rocks will make planter walls many other garden creations.
AND ALWAYS, when working with clay soils, pay attention to drainage paths in the yard, BEFORE constructing/planting anything. This is the perfect year to know how water moves through your yard to the street and if your neighbor's water flows into your yard, etc. I'm living with the result of MY OWN poor planning, which will mean a major tear-up to correct ... ie: HARD WORK ... drat!

    Bookmark   May 2, 2010 at 4:28PM
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corgicorner(Mass 6/7)

Why not dig down as you plan to remove all rocks, boulders, etc. Then replace the soil you have removed, and as you replace the soil add leaves, clean garbage, etc as you refill the hole.This will enrich the existing soil, making it useful to your future plantings. Good Luck!

    Bookmark   May 2, 2010 at 9:29PM
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Well I've gone ahead and excavated down to 1'. It is definitely hard work - where I live in San Diego we have especially heavy clay soil with the boulders and rocks. Excavation can only be done with a jackhammer fiited with a clay spade - hand tools such as mattocks and pick axes take forever, very tiring and highly dangerous - the rocks can shtter and cause injury (I got injured near the elbow doing this when I first started excavating the yard.

Here are some pics I took a couple of days ago.

Dirt pile

Another nice find - a big lump concrete thrown away by the home builers I guess. Had to break it up with the bull point chisel.

Bigger view of the whole bed.

    Bookmark   May 2, 2010 at 10:11PM
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That does look like what I remember the soil in San Diego looking like. I think the people that do the planting over at Balboa Park still have large compost piles and work organic matter into the soil they have to keep the plantings there growing.

    Bookmark   May 3, 2010 at 8:01AM
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darth_weeder(z7 NY)

blue can
I think you mislabeled that first picture
I don't see a dirt pile but I do see a rock pile
I'm with you though
I'd rather bust my butt and remove the rocks now and make life easier in the future.
good luck and post more pics.
I'm curious to see how many of those San Diego "potatoes" you dig up.

    Bookmark   May 3, 2010 at 10:57AM
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I've been told that the area I live in is somewhat more heavily packed with clay and big boulders than others. I understand that these boulders are some form of blue granite. Although they donÂt occur as frequently there are much bigger boulders. I have a few in my yard (I guess harvested by the original developers) that weigh around 50 - 60lbs each. In a shopping mall nearby they have some rather large ones - I would guess around 1000lbs each.

Here is a pic I took while lowering the soil level for the new patio. About 10 yards of rocks and soil. The clay is so heavily compacted they come out as big chunks. One chuck easily weighed about 50lbs.

Some people suggested using these as edgings but there are so many of them around here it is boring. I made some custom edgings out of concrete. I made moulds out of wood - the shape on the top was made by using a router and router bit actually designed for making crown molding.

    Bookmark   May 3, 2010 at 11:56AM
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WELL, SHUT MY MOUTH!!! Blue can ... here I was all full of folksy wisdom of how I transformed my rocky clay soil into killer loam![ALL it takes is SOME time and SOME organic material, and SOME effort] Your picture put that into perspective, big time! You could open your own rock quarry. I saw similar soil/rock ratio in the Mira Mesa area.

    Bookmark   May 3, 2010 at 1:15PM
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dchall_san_antonio(8 San Antonio)

Before I saw the cinder block wall I was going to suggest a tractor with rippers, a front end loader, and a dump truck. That would work for everything where there is not a wall. You need to be careful of plumbing and wiring that might be buried where you dig.

    Bookmark   May 3, 2010 at 11:56PM
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borderbarb - sorry I did not realize you are also in SD. I'm in Scripps Ranch which is near Mira Mesa - I have been told the soil here is worse than MM - but I don't know for sure. Not sure where you are but I take it your soil is not like this.

I only started putting up that block wall recently. It is going to be a natural stone veneer wall with stone caps - the block is just the shell. The real reason you cannot get heavy machinery in there is that there is a fence around the yard. As for digging into something - everything is in hand :) - I visted the city of San Diego's records department and have 4 large sheets of drawing/building plans for my house and the immidiate neighbourhood showing the layout of the plumbing, drains, storm drains etc. In fact I will be adding new drains to the new patio and those boards in the first pic is covering up a 2' deep hole which I dug to expose the storm drain line. I will be using SDR35 sewer pipe and attaching some new grate drains that will be in the patio. I'm also designing the overall grade so as to make sure drainage is not an issue.

    Bookmark   May 4, 2010 at 12:22AM
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Jebus, that is sorry looking 'soil'. That's not really soil, that's subsoil.

I think you have the right idea; remove the stones where possible, then cover that mess with imported soil. I don't see the virtue in trying to amend the clay subsoil and sand found between the rocks. It would take much too long and require way too many amendments. If you are able to remove the stones and replace the remaining subsoil into the bottoms of where the garden beds will be, that subsoil will eventually absorb organic acids and become fertile. But that will just be a side-benefit of having organic soil on top of the subsoil.

You might want to use the smaller stones for the paths between garden beds, but that depends upon the design of our garden.

    Bookmark   May 4, 2010 at 6:54PM
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blue_can a different opinion compared to what people said earlier. I always felt that soil replacement was the best option. I'm thinking of using EB Stone Organics Top Soil Plus (which is loam mixed with compost) along with one of their organic fertilizes. I guess that's what I will do (unless someone points out that it's not the correct thing to do).

    Bookmark   May 4, 2010 at 11:46PM
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dchall_san_antonio(8 San Antonio)

A fence is not an obstacle. You tear down the fence wide enough to get the tractor through and rebuild it when it leaves. My neighbors built a pool and had to tear down their fence and use my driveway to get back there. They repaired all the damage to the driveway and threw in a wheelbarrow.

    Bookmark   May 5, 2010 at 12:27PM
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toxcrusadr Clay Soil(Zone 6a - MO)

Yikes. That looks like the worst glacial outwash in the lower 48!

I'd consider washing those rocks and using them for ground cover. At my family home in Albuquerque we paid a lot of money to have 'river rock' like that delivered to the house!

    Bookmark   May 5, 2010 at 1:42PM
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You might also consider a few loads of mushroom compost. It is free at the mushroom farm. Might cut the expense. Depending on whether the 'look' you are going for is tailored or naturalistic...I have been very happy with the tree trimmings in my pathways. Very soft and spongy under foot and if I squint very hard, my yard looks like a small forest glade in the dewy morning.[fantasy]....Anyway, looks like you have put a lot of your ducks in a row and on your way to a successful garden. If you want some visual inspiration, go to the CA garden forum and click onto "My flower garden hit its peak" thread.
For more formal look scroll down to "Dad's flagstone patio"

Here is a link that might be useful: Pictures of CA garden

    Bookmark   May 5, 2010 at 5:00PM
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Thanks for the links borderbarb.

    Bookmark   May 7, 2010 at 12:26PM
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