Landscaping: What's a good depth for a raised foundation bed?

Replies: 19 Views: 112

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KaylyRed
Watertown, WI
(Zone 5a)

April 20, 2008 8:04 PM

I want to build a bermed bed against my east foundation wall. I can't dig the soil there to any real depth because all the underground utility lines run out from that wall (hence the need for a raised bed). What's a reasonable depth for the bed?

rebecca30
Fuquay Varina, NC
(Zone 7b)

April 20, 2008 9:42 PM

Minimum 6'' -10"
Maximum 12"

missingrosie
Hillsborough, NC

April 20, 2008 11:10 PM

Rebecca
Why do the beds have a maximum depth?

I have the same issue with the underground utilities - propane, etc., and the ground is very hard and all clay. I thought to do a large raised bed next to the house to include the generator. I need a fairly wide space to plant shrubs, etc. to disguise the generator and to shape the planting area the way I want to do. I thought to make it fairly deep to accommodate the roots of a few small trees and shrubs. I think I will need more than 12 inches. Did you read somewhere it shouldn't be deeper than that?

KaylyRed
Watertown, WI
(Zone 5a)

April 20, 2008 11:31 PM

Thanks, Rebecca! I'm curious about the maximum depth, too. Is it not good to raise the soil a certain level above the foundation, or something of that nature?

pastime
Waterman, IL
(Zone 5a)

April 21, 2008 7:55 AM

Get your local JULIE man out there to flag where your utility lines are located. Then you can dig around them.

KaylyRed
Watertown, WI
(Zone 5a)

April 21, 2008 10:47 AM

Quoted:

Get your local JULIE man out there to flag where your utility lines are located. Then you can dig around them.

Oh, I know exactly where they are for the moment. They were flagged last fall when we had to have a new mound septic system installed and I left the flags there. But the way I move plants around it's a lot more practical to have a raised bed than to try to remember where the utility lines are all the time. Our Digger's Hotline guy would get pretty irritated with me every spring, I bet. ;)

Might not be a bad idea for missingrosie, though. If you're planting shrubs you're not prone to moving them around. Once you know where the lines are you can plant and then forget about it. I would think you'd just want to plant so that the root system for the shrub won't interfere with the utility line.

ecrane3
Dublin, CA
(Zone 9a)

April 21, 2008 11:24 AM

You do need to be careful about piling soil up around your foundation, it's generally not a good idea to do that. So if you do want to build a raised bed, I'd build one with 4 sides (as opposed to using the wall of your house as the back side), that way the soil won't be in direct contact with your foundation.

missingrosie
Hillsborough, NC

April 21, 2008 1:08 PM

Our land slopes down from the house foundation, and so the depth would be less as you get close to the house. Farther out --enough to scoop up the generator the slope would be greater and the raised bed depth likely higher than 12 inches. Plus I thought that the deeper the better for the roots. Next to the house would likely not be built up at all. The ground is just too hard to dig into; the utility lines are less of an issue. I have them marked also. I was just wondering about the 12 in max depth that Rebecca mentioned. I planned on a retaining wall farther out from the house that is higher than that.

ecrane3
Dublin, CA
(Zone 9a)

April 21, 2008 2:03 PM

I wonder if she was thinking about the soil against the foundation thing and was thinking 12" would be OK but deeper wouldn't? Or maybe it was rules about retaining walls, here if you build anything taller than 3 feet you need a permit but different areas probably have different rules on what height you can build w/o a permit.

I wouldn't worry too much about the depth, get it deep enough that you can get things planted, but remember you do have soil underneath there, so if the plants' roots need to go down farther they can go down into the original bed underneath (unless you have hardpan/caliche right near the surface, but that's more of a problem in places like TX and the southwest)

missingrosie
Hillsborough, NC

April 21, 2008 7:03 PM

So you think that the hard clay (I think we do have another 6 inches or so maybe 8 of good dirt before we hit that hard hard hard tan/taupe clay --not the red stuff the tan stuff) can be penetrated by roots? Is it because the raised bed sitting on top softens it? I cannot imagine how a root could go down into that stuff...I think it would head sideways.

rebecca30
Fuquay Varina, NC
(Zone 7b)

April 21, 2008 7:37 PM

Missingrosie - in answer to your question, when I did my research about retaining walls (whether stone or wood) I found, like ecrane3 mentioned, after a certain height it won't be stable. Usually 12 inches is deep enough for most plants, unless you want to to bushes or something that require perhaps more room. If you think about the top soil portion of the natural ground, most root systems are happen in the first 12 inches or so.

If ya google around, you will get a feel for how high and wide, etc etc. For me, I did it 12 inches tall since I knew most of my perrenials will be just fine within the first 6 inches of dirt or so. It a just a rule of thumb and it also depends on the look, your needs, amount of $ you can spend on materials, etc

rebecca30

This message was edited Apr 21, 2008 7:40 PM

rebecca30
Fuquay Varina, NC
(Zone 7b)

April 21, 2008 7:46 PM

Here are some helpful website to give you an idea of what's possible. For me I didn't want it too high. :o)

[HYPERLINK@www.raisedbedgardeningtips.com]

[HYPERLINK@www.helpfulgardener.com]

[HYPERLINK@www.essortment.com] Here a quote from this website: "Most plants will need at least 6-12 inches to root properly, consequently, adjust the depth of your bed accordingly. Beds of 18 inches and higher will need a retaining wall. To build the retaining wall of your choice, look for detailed plans and designs in publications at your local garden supply store. "

I hope that helps you out. :o))

rebecca30
Fuquay Varina, NC
(Zone 7b)

April 21, 2008 7:47 PM

Here my bed, in the middle of everything: so 12'' worked just fine for my purpose

View Larger

missingrosie
Hillsborough, NC

April 21, 2008 8:02 PM

It does. Thanks. I am definitely not going to build a retaining wall. I think that would require a landscaper and I have spent the budget for that and now must do the rest myself. I have a japanese maple planned for that area, and abelia, pieris, lorapetelum, etc. so I will have to research the root needs.

bonjon
Raleigh, NC

April 24, 2008 5:39 AM

missing rose - that hard stuff down a bit - my dad always referred to it as "hardpan". My carolina red clay goes down quite a bit more where I am that where you are because I can go down over 10" and it's still red. Dad called hardpan "sunbaked brick" when we couldnt' get a pickax through it!

But ecrane is right about soil next to the foundation walls, and clay tends to retain moisture more than sand. you shouldn't pile any extra against your foundation directly. your builder probably planned for or helped grade that sloping ground away from the house.

missingrosie
Hillsborough, NC

April 24, 2008 8:26 AM

That tan stuff is unbelievable. When I hit it with a shovel the shock goes up my arm and rattles my brain. Thanks for all the info and advice!

bonjon
Raleigh, NC

April 24, 2008 1:05 PM

well, all I can tell you is all these loblolly pines (Tarheel state, right?) send taproots into it!

bonjon
Raleigh, NC

April 24, 2008 1:08 PM

;)

:)
got to admit, I get a hoot out of yankees coming down here telling me our carolina red clay and hardpan won't grow anything...then the Californians arrive and swoon over us "living in a national park" hehehehe

heavenscape
JayeVille, NC
(Zone 8a)

April 24, 2008 1:13 PM

Lol Bonjon and MissingRosie!!
I was 'spoiled' till I move here. The soil won!! So, this year, more raised beds for the flowers, and strawbaling for the veges.
Easier on my back, moreover gypsum's not that cheap and can't find river sand around here!

bonjon
Raleigh, NC

April 24, 2008 2:53 PM

what's river sand?
I have concrete place deliver mortar/contractor sand - harsher grit. if you add fine sand all you'll make is high grade concrete!

this clay will grow just about anything, full of minerals. it has to be loosened and lightened is all.

Kayle - I'm with you though. My Uloco man knew my address from heart because every spring, and every fall he's had to locate the gas line that runs through my iris beds!

Gypsum is same price as lime and I use both equally. - a pretty cheap chemical !

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