Fill soil

My back yard slopes, not an extreme slope but enough that it's an issue for gardening. I'm looking at close to a 5 foot drop over 120 feet. I'm thinking of creating two terraces, an upper "yard" terrace and a lower garden terrace, supported by retaining walls. Each retaining wall would be approx. 2.5 feet. Rather than simply level my soil, I'm thinking I'd rather add new, because under a thin layer of decent topsoil, I've got heavy clay.

The obvious option is to have soil delivered from a local company, but that's a lot of soil and cost. By my calculations about $10,000 of soil per terrace for screened topsoil. I might go this route despite the cost but am interested in alternatives and/or cautions about the idea. One possibility I thought of was to do most of the leveling with wood chips that tree services will provide for free or at low cost -- perhaps something like hugelkultur -- topped by a layer of screened topsoil. But I'm thinking as the wood chips decompose, they will subside and require additional topsoil to be added. This could be a problem if I don't want large machinery driving on my ground every year or few years.

Does anybody have other ideas, or affirmations of either idea I've mentioned above? Good sources to look at for further info?

Thanks.

Brian,

“Fill woodchips” is a cool idea but they will definitely sink over time.

I actually think that this is a really good idea, but it does need some planning in advance.  First question though:  is this to be a yard or a garden.  If is the latter, woodchips are an option, but make no mistake, they will shrink drastically as they decompose.

A possible way around this issue is to mound up the chips where they will shrink the most.  I presently have a pile of wood chips that I chipped up this spring.  It used to be about 7’ tall.  Now it is something under 6’ tall—most of that drop is pure settling.  So if you mound up the chips, really mound them.

My instinct tells me that this could be a winner for you, but you might have to add in more chips as time goes on.  It may very well take a couple years or more to stabilize, but eventually they will stop shrinking.  And that much woodchips will make some amazing bedding!

Just a thought,

Eric

Thanks Eric. I'd mainly think of taking this approach on the garden terrace due to the compacting/subsiding issue. I've already got a mound of them in my yard so I've been watching the compaction too.

It's hard to visualize entirely but given the costs you quoted I guess we're talking a large space.  Here's some things to consider that might be a trainwreck of an idea but maybe not?

Retaining walls are heavy, expensive, and hard to engineer.  They often buckle or bow if moisture or soil expansion is an issue.

The square foot gardening approach says that you can put a raised bed straight on concrete if you want.  You only need a foot of potting mix at the top, regardless of what is beneath.

So I'm thinking, instead of retaining walls, some form of tasteful planters/serpentine plant beds that either have cheap filler below or nothing below.  Perhaps corrugated irrigation tubes turned sideways, or cantilevered growbeds?  I'm saying skip the retaining wall and $10K of fill and instead build something to support 12" pf potting soil mix.  

Rob does make really good points and raised bed gardens can be very nice for planting, maintaining and harvesting.

Again, just a thought,

Eric

When we built our new house we had a big area and quite a grade.  Some of what you could do depends on the type of look you want.  I could not afford to do it all at once so I had BIG rocks placed at intervals and backfilled behind them.  Then more BIG rocks and more backfill.  I made beds working my way across the yard and down.  I made stairs between levels of beds.  It’s nice.  It’s not bad for maintenance as I mulch the beds.

My concern with retaining walls is I’ve never seen any that didn’t move or break down over time.  I have to agree with the previous post.  And...I like a more “natural garden “ look..not so formal.

And I love BOULDERS!

About retaining walls and complexity/maintenance/failure: this is a concern of mine too. I'd most likely hire pros to do it in hopes of greater durability. Also would hope that being relatively short (<3ft) would help.

Good points from Rob. The spaces is approx. 60x90 feet. Part of the reason I'm thinking of the terracing vs. planters and beds is I love the look of terraced hillsides. The cost is definitely high and it would be hard to justify from a productivity perspective alone. But if I go ahead with this I am expecting it to be very esthetically pleasing as well at least to my tastes. At this high a cost, I appreciate all the skepticism that might be thrown my way to make sure I think through things.

Brian Rumsey wrote:My back yard slopes, not an extreme slope but enough that it's an issue for gardening. I'm looking at close to a 5 foot drop over 120 feet. I'm thinking of creating two terraces, an upper "yard" terrace and a lower garden terrace, supported by retaining walls. Each retaining wall would be approx. 2.5 feet. Rather than simply level my soil, I'm thinking I'd rather add new, because under a thin layer of decent topsoil, I've got heavy clay.

The obvious option is to have soil delivered from a local company, but that's a lot of soil and cost. By my calculations about $10,000 of soil per terrace for screened topsoil. I might go this route despite the cost but am interested in alternatives and/or cautions about the idea. One possibility I thought of was to do most of the leveling with wood chips that tree services will provide for free or at low cost -- perhaps something like hugelkultur -- topped by a layer of screened topsoil. But I'm thinking as the wood chips decompose, they will subside and require additional topsoil to be added. This could be a problem if I don't want large machinery driving on my ground every year or few years.

Does anybody have other ideas, or affirmations of either idea I've mentioned above? Good sources to look at for further info?

Thanks.

Hi Brian. I was gonna suggest hiring a bulldozer, if you were willing to pay 10k$ anyways, it would be cheaper. Now I see that you said you didn't want to level it. In that case heres an option you might want to consider. Around here saw mills are often giving unlimited amounts of sawdust away for free. You just have to pick it up from there. It's basically the same idea as wood chips, but easier to acquire. We got a truckload and made raised beds from a mixture of sawdust and clay dirt, like you mentioned. The plants didn't do real well though. Later in another garden we tilled in woodchips, that we had used as mulch the previous season. Those plants had some problems too. Eventually, we came to learn that wood decomposing in the soil leeches nitrogen to aid in it's decomposition. In both cases the plants didn't die. But they were very sickly. So, that is something to consider. Still though, it might be worth it, rather than buying 10k$ in top soil.