8-10" of excavation is a lot ! Sounds like a major rehab project. How big is the site?

Since I take it the soil is outta there already, the question now is what goes back in it's place, and a related issue is how do you maintain it (the soil). The answers will depend in part on what is going to be planted in that space. But first, relax about the subsoil 8-10" down - I'll comment on that a bit lower.

If what will be planted will be permanent landscape, then topsoil would be just fine, and is actually overdoing the topsoil a bit (and 8-10" of topsoil is a lot). A key to maintaining it is to then cover with a good quality mulch, preferably wood based. Keeping it in good shape means topping off with new mulch periodically - once or twice per year depending upon your climate and how fast the mulch degrades.

For annual planting areas (flowers, veg's, etc.) you can go higher on organic soil amendments, and add additional amounts of new organic material annually. The target here would be ~ 5% by weight (10% by volume) total OM in the soil.

The reasons for the difference is that the OM in the soil will basically be gone in Chose your soil to bring in based upon what will be planted, and then maintain the soil accordingly.

As for the subsoil 8-10" down from where your final grade will be, it will take care of itself if you take care of what's on top.

For reference, I suggest you visit Linda Chalker-Scott's website (aka The Informed Gardener), link below. Of particular interest to your case are two "myth buster" articles she wrote. You will find them (and others) via the "Horticultural Myths" tab at the top of the column on the left side. On the Myths page scroll down to near the bottom and find the section under Soil amendments

The first one to read is about amending clay soil - you'll find it at the bottom of the Myths page via the link Sand. While that's not your issue, she explains sensible soil amendment for horticulture.

The second one I recommend is still in the section on soil amendments under the heading "Organic matter" - it is the link 3. Nutrient overload. In that she discusses the perils of overdoing organic matter additions to soils.

You might also check out some of her Landscape Rehab Projects via the tab on the left side.

Good luck, and let us know what you end up doing. A pic or two would be nice too.

Here is a link that might be useful: The Informed Gardener

This post was edited by TXEB on Mon, May 13, 13 at 19:10

hi txeb!

thanks for the links, detailed response, and better feedback. i'm working with a pretty large site with three main areas (see pics below): the backside corner of my house - has moderate shade, direct backside of my house - direct sun, and side of the fence - direct sun. i plan to plant a variety of shrubs, plants, and tree's but haven't designed my layout yet. i plan to focus on each area at separate stages. from your advice i plan to work with 6 inches of soil blend and 2 inches of mulch.

do you recommend i cultivate the subsoil with a tiller or pick/fork before i add the soil blend? i read on the interwebs today that if i don't, the subsoil can act like a bathtub to the soil blend/mulch. what's your take on smothering the subsoil with a layer of newspaper or plain cardboard and covering it over with the soil blend? or do you think i'll be allright just spreading the soil blend over the subsoil?

thanks again for taking the time to respond. i feel like the more research i do on the web, the more i get confused. your advice is greatly appreciated!

best, norm

second pic

Norm - good pics, helps a lot.

Based on what you say you will be planting, I would forego the soil blend and go with a decent topsoil, and use at least 2" of a good wood mulch, 3" would be even better. Forget any idea of newspaper, cardboard, etc. on top of the native soil.

The "bathtub effect" arises when you dig a hole in a poorly draining, high clay soil, then fill it with a soil that is very permeable to water - think cereal in a bowl. You have a bit of a bowl. Tilling the native soil, then going back on top and filling over won't do much for the underlying soil structure - it will rather quickly settle and return. You could add about ~3" of the topsoil, till that into a depth of 6", then finish with the rest of the topsoil. With 2" of mulch, that would give you a ~3-5" top layer of the topsoil, with a 6" layer of 1:1 topsoil: native soil beneath.

I would avoid the high organic content soil blend you described, and I wouldn't blend in any compost or other organic matter as you prepare the base planting area. The organic matter will decompose faster than you think, and with all the permanent plantings you can't get it back into the soil to compensate. The preferred approach would be an appropriate topsoil and a degrading mulch on top. Once it is filled an planted, nature will take care of the soil OM; growing plant roots will do the tilling for you. If you will have annual planting areas, you can add some compost to the base soil before you plant them (some means about 10% by volume or ~ 3/4" for the fill plus mulch). It's probably hard to imagine, but the plants will fill the surrounding area with roots that you won't see, and they are natures tillers. So long as the roots can readily expand and develop it will be just fine.

I know the soil blend looks really attractive, but its really NOT the right choice for permanent landscaping. It would be a decent choice for an annual plant (flowers, veg, etc.) raised bed on top of the base soil, but it's not a good choice for a base soil.

edit - added note - a real key to the long term success will be to choose plants that will grow well in the base soil you have.

This post was edited by TXEB on Tue, May 14, 13 at 4:34

What is decent "topsoil"? The only definition of "topsoil" I have seen is that it is the top 4 to 6 inches of soil from someplace. Conversations I have had with many people over many years tells me that what they have in mind is a soil that is about 45 percent sand, 25 percent silt, 25 percent clay and 5 percent organic matter which is what loam is defined as. Loam is not very availlable although many people do have it, but there is not enough in the world to supply everyone that wants it, unless you have a landscape supply house that mixes soil to that formula.
If I were to look for soil that is the soil I would look for.
The bathtub affect is when you have a drainage problem and water accumulates in the planting hole because it cannot get out. Most usually this occurs in small planting holes although it can occur over wider areas. The bright spot here is that if you prepare your soil properly and get a good, active Soil Food Web they can change the subsoil so it will drain, eventually.
Some people may tell you that you should get very large amounts of organic matter in to your soil and, as Dr. Chalker-Smith states, that can create problems. I have found, over many years, that a level of organic matter, humus, in the soil of 6 to 8 percent is optimal and that level in very large beds does not, in my experience, cause water accumulation problems that higher levels of organic matter can.

kimmsr - at least you're consistent. Are you always so grumpy and contentious? The OP asked for input on how he should proceed from where he is now in the midst of a sizable DIY landscaping project for permanent plantings. How does any of what you posted help him? This isn't the time or place for an academic debate.

In my experience I've never had any trouble getting "topsoil" from a reputable soil yard, and it has always been either a loam or a sandy loam. That includes where I live now, in the heart of TX gumbo clay country, where topsoil is readily consumed by the expansive action of our native soils. I just opened my telephone book and in the yellow pages there are four ads under "Landscaping Equipment & Supplies", three of which offer "topsoil". A good, reputable soil yard will be able to tell you the composition of the topsoil they have.

This post was edited by TXEB on Tue, May 14, 13 at 9:13

Norm - should have suggested this to you sooner ... ask the soil supplier you are considering for that blended soil what the percentages of WonderGrow Organic Compost, Rice Hulls, Chicken Manure, Grape Compost, Fir Bark, Cocoa Bean Hulls are, and also whether those are weight or volume percentages. Then add them up. The sum will give the initial fraction of organic matter in that soil. If it's much over 5%, my earlier concerns stand. If it's 5-6% or less by weight, then basically it is sandy loam and would be fine to use.

You might also check if they have "topsoil" and it's composition. Presumably they have sandy loam as it appears to be the base for the blend.

Keep us posted - looks like a "fun" project

I suggest more than 2" of mulch. I like to be at, at least, 4".

Norm - hope you pick up on this .. hopefully it's helpful for your project. I would have included this for you earlier, but I had this info stashed and it took some hunting for me to re-find it.

For any soil that goes into landscaping there are three classes to know: bank soil, loose soil, and compacted soil.

"Bank soil" is soil in it's naturally settled state, without machine or human compaction. An open lot, untouched, would have a bulk density of bank soil.

Dig that soil up and the bulk density decreases as it becomes broken and aerated. That is loose soil.

Take soil and compact it, like running machinery over it, it becomes compacted soil.

The typical relationships for bulk density are bank soil is the reference = 1.0, loose soil expands and has 80% of the bulk density of bank soil, and compacted soil has a density about 1.05-1.1 of bank soil.

Why is this important? A big part of permanent landscaping is establishing a stable and permanent grade. You want stability after installation. When you buy soil for a landscape you get loose soil. But when you are filling and grading to native settled soil you have to match surrounding bank soil for grade and drainage. That means for a soil comparable to the untouched surrounding soil you will actually need to overfill and gade with loose soil to allow for the settling. Typically by about 10-20% for topsoil. The soil supplier should be able to guide you on how much.

The danger is that if you don't allow for that natural settling, you will end up with a low area where you had filled as it later settles, and if that area is planted for permanence there is little you can do without upsetting the plants.

A part of the consideration is the filling soil's organic content. The more of that there is, the more the soil will settle over time - it cannot be directly replaced in permanent landscapes. You can only strive to maintain it via top dressing / mulch in those permanent grade and planted areas. About as good as you can maintain that way is ~ 5% organic matter. If you start with a higher OM content, then you need to allow for that much additional settling over time.

This post was edited by TXEB on Fri, May 17, 13 at 3:34

hi TXEB!

I missed your last post, but am glad i caught it today. i re-visited this thread since i'm purchasing mulch for my project his weekend. your bulk density post is very timely. after spending a weekend of wheel barreling and shoveling top soil, i was wondering if i calculated the cu yard of topsoil amount correctly since the top soil was loose and sunk when walked over it. that 8 inches i accounted for seemed to be more like 5-6 inches once i took a step on it. according to your last post it sounds like i need to add an additional 20% of top soil. How can I establish a stable and permanent grade for my loose top soil? run a hose over it with water? walk over all over the top soil? or will it naturally settle? how long do i have to wait until the top soil is stable enough to plant? thanks again for taking the time to help out. i truly appreciate your expert advice!

This post was edited by NORMdaWORM on Thu, Jun 13, 13 at 1:01

oh, one last question. regarding mulch, any suggestions or recommendations. i'm considering fir bark 3/4 inch and redwood chip mulch:

redwood chip mulch $29.00 cu yard
A ü to þ-inch redwood chip mulch. Used for mulching and on pathways.
vs.
fir bark 3/4 clean $50.50 cu yard
Fir bark chips excellent for mulching and pathways. Small size lends itself well to meticulously detailed gardens. Also known as Mini Bark.

any advantages or disadvantages either way?

thanks again!

Howdy Norm. I was wondering about your project and how it was going.

For settling, you don't want to go to the compacted state, so it's a bit of a line to walk. I like a lawn roller - one of those water filled drums with a handle. Roll all over it in cross directions, and walk all over it. When going from loose to bank, it will compact about 20-25%, so 8" should become ~ 6". Put that in, roll it, then top it off for the final 2" and rake it out to final grade. I like to fill in 4-6" lifts, roll in between. But at 8" it should be okay. Then water it well a few times, and you should be set to go.

On mulch, I'm not familiar with those west coast materials, but they sound fine. The fir bark sounds premium, but it also comes with a premium price. Consider how long they will last as part of the value equation.

Sounds like you're getting close to being ready to plant.

Thanks you! I will follow up with photos & keep you updated on my progress.

Norm, are you adding any raised beds on top of the finished base grade?

I don't plan to have raised beds for this area of the house.

Cool. That makes it easier