I think most sources recommend 12 inches deep. I have a garlic bed that is 8 inches deep, the other two are 12 inches deep. I've seen people make raised beds as deep as waist high, to make it easier for gardening with less bending. I've even seen raised beds on stands that the bed itself is a foot or so deep- again I think it's to make gardening easier.

The All New Square Foot Gardening book by Mel Bartholomew says a 6" high box using Mel's Mix as the planting medium is all you need. Many people follow this plan. But my boxes are between 10" and 12" tall. That helps to keep my soil from drying out in my heat and allows room for mulch in the box.

I love Mel, but he is dead wrong on the idea of 6" deep beds. That is far too shallow and much too prone to shock to the plant from heat, drought, and almost any little thing.

The only reason a raised bed needs to be actually raised is if you have a drainage issue. Raised beds have advantages but that's the only reason you HAVE to do it. And then the amount that they are "raised" would depend on just how bad your drainage issues are. If they're REALLY bad, your raised bed might end up on stilts, LOL!

I also never ever ever put weed block in the bottom of a raised bed built on the ground. That just keeps the worms from doing their job, which is to make ALL your soil nice and fluffy.

I build my beds on top of whatever soil I'm given, and thankfully I've never been given soil so bad that it was irredeemable. I generally don't even add soil to the bed unless it came from the path.

What I DO do is lay down a double layer of cardboard as weed block and cover that over with whatever mulching material I can lay hands on for free or cheap and which won't (in the case of being in town) get me a visit from the local Lawn Nazis.

Hay, straw, leaves are all good, but sometimes hard to come by in the suburbs or in the city. Lawn clippings are not good - they will mat, shed water, and sometimes start to rot right in your bed causing all sorts of problems from becoming a source of fungus and gnats to just plain stinking. Grass clippings belong either on the lawn or in the compost bin.

If you are in a city where they collect lawn waste you can often get mulched yard waste for free or cheap - that's a good mulch to use. And if all else fails, I use cedar or pine bark mulch from Home Despot. Just make sure you don't get the dyed stuff - it is chopped up demolished houses and aside from the dye, may have pressure treated wood in it. The old kind. With the arsenic.

The first year may be rough but it just keeps getting better after that.

I have never understood this turn towards treating the raised beds as if they were giant containers. If you treat them that way, they're not even GOOD containers - not if they're only 6" deep.

I just built a 6" 4x4'. It was scrap wood so I did not choose the depth. I put down cardboard over clay, Bermuda and St Augustine grass. The bed was filled with city compost + 5 gallons of dried cow manure (not composted but not stinky). All was free.

Because of the E Coli possibilities, I plan to wait 6 - 8 months before using the bed.

Bermuda is already becoming a problem and I pull it two or three times a week. With no room for mulch, I can see this as a problem.

Next bed will be at least 10" where I can put 6" of Mels mix or a close alternative. Then I can still add 4" of mulch. I really don't want to spend so much time pulling weeds and watering.

There is another reason for raised beds ... the soil warms earlier in Spring.

This post was edited by slowrider on Mon, Oct 13, 14 at 12:52

I am 55 years old, 5' 2", and a woman with a disability. I scoot along with a garden seat these days. Ticks me off that I can't get up and down like I used to, but there you go.

And the only reason a bed NEEDS to be raised - is if you have drainage issues, regardless.

Actually I'll grant the advantage for soil warming - but that's slight unless you are living in a short-season area where that's a problem.

If you want a raised bed for reachability that's one thing - but the soil itself does not require it.

I should have said - I ALWAYS work peat moss into the soil the first year or two. After that, the worms have been at work enough that they are pulling the mulch down into the bed and things are vastly improved. I don't have the money to fill a raised bed with material that isn't really suitable for gardening in the ground anyway. It's cheaper to hire somebody to come out and chop at the ground FOR me, if that's what it takes. Especially since that still needs to be done.

6" is not enough. I've been gardening for most of my life, and square foot gardening in raised beds for at least 30 years. I used to garden to can. Harvest size mattered to me when I had a big garden, and it still matters now that I'm restricted to much smaller gardens. I haven't got the energy to waste on a lot of space or poor producers.

Heck, I plant my tomatoes deeper than 6" - and a carrot hasn't got a chance in that space, LOL!

As for weeds - unless you are starting over established sod, cardboard and mulch takes care of most everything, and what's left is easy to kill.

For starting over sod, I'd use the cardboard and mulch (NOT bark mulch in this case but something that is already at least partially composted, or straw or hay or whatever you can lay hands on), work that into the soil when its rotted pretty good, then solar sterilize. THEN build the sides of the raised bed. Sod is hard to kill - you need to be sure you have killed every rhizome.

6 inches of M.M. is fine for most plants, Mels recommendation is good if you have the time to work your garden continually.
Elevation issues are all different for many, comfort, disabilities,
roots, etc all enter.
I recently elevated my 4 beds at considerable cost because of tree roots.
At 30 inches now I am happy it's done..My back is happy also.
I still only have 6-8 inches of MM
Everything comes down to " Whats good for me ) meaning you

Unfortunately, tree roots will happily grow upward into the raised bed.

Yolos .... If you start with an open-bottomed raised bed 6-8 inches high, fill it with a rich compost/dirt mix layers and plant some deep-rooted vegetables as well as salad greens and shallow rooted things you can improve the soil under the bed with very little effort.

Okra is dynamite for busting through hard-packed clay and improving dirt. Its roots go down 4-6 feet, and when they decompose you have open channels and organic matter that deep. Just cut the plants off at the base in the fall and leave the roots. Plant more the next year.

I started with hard-pack AZ desert dirt so hard I needed a pick to make planting holes. But with repeated layers of wood chips and compost and drip irrigation, and planting okra I can now use a hand trowel anywhere in the veggie garden.

Thank you for your advice lazygardens. My beds were placed on top of well established pasture grass of some type. I was able to scape off the grass on top but did not want to go hacking at trying to remove the roots. I put down a layer cardboard. Every year, before planting, I have been punching the ground in the bed with a garden fork and wiggling it back and forth. This has broken up the cardboard and allowed compost and good dirt down into the red clay. Every year the fork goes further down into the clay but I still do not see any worms in my beds so they have been no help to me in breaking up the soil under the bed.

This year I started cover cropping in the beds in the fall. I bought some daikon radish seed but never got that planted. I did plant some winter rye and winter peas. My problem is most of the garden only gets 3-4 hours of sun in the winter because I have a forest behind my garden and the sun just skims the top of the trees in the late fall and winter. I have planted okra in two of the beds the past two summers.

Anyway, I would still use 10 - 12 inch tall boards because of heavily mulching. The difference in cost of a 6" board and a 10" board is not significant enough for me to use 6" boards.

My reading says 6" of soil......I have a raised bed 30" high for convenience....with a sheet of steel roofing laid in just below the first top side board level...I used 1" x 8" so that makes my soil approx. 7.5" deep....works great for herbs, lettuce etc....

My big bed is railroad ties....4 high (32") on the front and 1 tie high on the back as my ground slopes...& it is 3 ties long (21')and full of rock then dirt.obviously this is permanent.......this is where I plant tomatoes and am able to drive stakes down enough for them to hold up vines 5-6' high to horizontal bars etc....most of my vines go up to 6' and then turn over and go almost to the ground...but the dirt is deep enough to hold them up all summer....Beans, zuch. and others easy to harvest and work at this level....

My front bed is 2 boards high (sawmill....rough cut....1x6x10') and 3 lenths long....30'......so is approx 12" deep and on the ground..I made it narrow as it is behing a flower bed...approx. 1' deep.....I'm thinking of putting asparagus there.....

So you may see they can be all sizes to fit YOUR needs and preferences....I'm 70 and don't like getting down on my knees to weed or bend over as my jeans shrunk and are tighter than when I bought them.....cheap cloth I guess........so I really like the 30" hgt. ..... :)

RABSR
We must have shopped at the same store, I had same problems with my jeans.
The 6 inch height is the recommended number.
Mine are 8 to 12 and may be higher when I do the potato's this year..
I was pleasantly surprised after the first season when pulling up tomato plants.Roots the size of cigars running 3 feet across.

I have used raised bed with weed mat under Mel's mix that are 6" deep for 5 years. I grew enough to keep me happy. I also had shade for part of the day. Now that the boxes are crumbling, tree roots and shade invading, and two spruce blown down in a microburst, I am moving my beds to a sunny area and using concrete blocks which are 8" deep. I have terrible clay that I am just about finished with as I am approaching the senior years. In the 8" beds, I grew enough food to process and had to buy a freezer. I'm sure the additional sun helped. I also found I didn't have to water as often. My husband capped the top of the blocks with patio blocks and it looks pretty good.
Keski

All of mine are a minimum of 14" deep in NW Alabama, because the summer heat is just too much for any other depth. More soil depth allows for less watering frequencies, and also keeps the plant roots cooler.

EG

All of mine are a minimum of 14" deep in NW Alabama, because the summer heat is just too much for any other depth. More soil depth allows for less watering frequencies, and also keeps the plant roots cooler.

EG

wouldnt it depend on what you are growing.. and what is below???

if its on top of concrete... it better be deeper ...

but if soil below ..... and then the plant [or all plants you might ever contemplate] ... would dictate how deep it need be .. its one thing if you are growing radishes.. another if you are thinking horse radish and potatoes ...

then you throw in wheelchair height/health issues ...... etc .... those would be non-garden specific variables ....

ken

Ken
What is below shouldn't matter as there is a layer of weed barrier I had 9 tomato plants in 9 squares, 7 inches deep. some grew 3 feet in a horizontal direction. M.M. when correct will allow root systems to grow anywhere..(IMO)...I believe the real secret is in the compost.

I mostly grow in 6 inch raised beds (they were filled with compost and soil) with no weed barrier. Underneath the raised bed height is a good foot of well-amended soil that plants can root/grow in. I mix in shredded leaves and grass clippings every fall. And I either use homemade compost as a topdressing or mix it in, depending on how much I've got and when. Most things I plant grow well (except potatoes, I can't figure them out).

Rodney

I have raised beds for 2 reasons. I am older and bending way over is not too good and will more than likely get worse.

2nd- I have moles, voles, gophers and ground squirrels !!! No lie! My beds are 3' W x 16' L x 18" high. On the bottom of my frames I have attached 1/4" hardware cloth to keep these critters out. An absolute must or why bother having a garden!

I also live in the Sierra Foothills where summer temps are daily in the nineties and winters average over 50" of rain. So I need the depth for cooler soil in the summer months and for drainage in the winter months.