ideal depth for raised beds

has anyone done any experimenting with what would be the ideal depth for raised beds? how deep should they be to give plants optimal root growth and not allow any weeds from popping up from native soil from bottom. ive had such serious problems with native grasses and weeds was thinking of trying raised beds filled with bales of potting soil

Our raised beds are based on the avaiabilty of the size of lumber.

Two 1' x 10' will make a 12" high bed that is 5' x 5' x 12".

Twelve-inch deep beds are plenty deep for most vegetables.

Most garden beds are built over a base of dirt so most bed heights still give the plants room for their roots to go deep down.

We once had a bad idea of using a kiddie pool for a garden bed.  Bad ideas as the plants were root bound so the next year we cut the bottom out of those kiddie pools.

Another consideration for garden bed height is age.

Older folks may have trouble getting down on their knees to work on low beds.

Then there are folks with back problems that need higher-height garden beds.

Unless making beds over concrete or bedrock most garden bed heights are okay.

I am looking forward to what others feel are good garden bed heights.

Six to twelve inches is the standard for good root room for your vegetables.   Avoiding weeds coming up from the bottom will depend on what weeds you are fighting.  My worst weed is our grass and we find we need to dig weed barriers six to eight inches underground and a few inches above the soil all around the garden.  We use aluminum flashing for this purpose and a rock border to protect the easily bent raised portion. That border also protects our easily cut skin from a rather sharp edge.  

These are in ground beds so weeds are struggling through compacted lawn to get deep enough to rise again.  I have seen our grass send runners 5 feet straight up through a mulch pile which is why most lasagna gardens start with cardboard. If you aren't clearing the ground before building the bed you might want to consider that also.

Edit:  inches underground not feet! We're near bedrock here.

I've done a few different types/heights, & it really just depends on what you want to grow there for root depth.  I do like the 1"x12" boards on edge as mentioned above.  I've successfully grown potatoes in this setup for a few years.

I think everyone's advice is right on.  A foot is plenty.  I am experimenting with building some beds that are 3 feet high just to keep from bending or kneeling as Anne mentioned.  These beds are kind of a long term experiment for me.  I'm making them by building compost piles and continuing to add material as they sink.  I have no idea how long it will be until the are the proper height.  My plan is to make a couple hugel kulture style to save on materials.  I don't know if wood in the bottom will hold more moisture than pure compost will.  I guess I'll find out in a few years :)

Trace Oswald wrote: I am experimenting with building some beds that are 3 feet high just to keep from bending or kneeling as Anne mentioned.  These beds are kind of a long term experiment for me.  I'm making them by building compost piles and continuing to add material as they sink.  I have no idea how long it will be until the are the proper height.  My plan is to make a couple hugel kulture style to save on materials.  I don't know if wood in the bottom will hold more moisture than pure compost will.  I guess I'll find out in a few years :)

I decided on 30" high for exactly this reason - that's standard table height, and I'm not a particularly tall person. The two newest beds I built are ~4'x6.5' because I based it on some pallets I was able to get. One of them has quite large rounds of punky wood in the bottom, the other has a bunch of miscellaneous scrap wood. They both have compost mixed with crappy dirt on top and both sank a fair way over last season and I didn't manage to top them up in the fall (last fall's weather was crappy here.) Where most people here have to water veggies once/day to keep them alive, mine will go 2-3 days generally. I suspect that's a combination of compost that's got some biochar mixed in *and* the punky wood.

However, what's significant to the OP - there are weeds that have still come all the way up - particularly Morning Glory, but also Himalayan blackberry. However, with this tall a bed, it's much easier for me to knock them back a fair way. They're both thoroughly invasive to my garden area, so it will be a constant job to try to catch them small and pull out as much of the underground bits as I can. I use various techniques to make sure they don't reproduce further, but I suspect that with the Himalayan Blackberry, it's a loosing battle. At least the berries make great jam, crumble, ketchup, animal feed...

We have short beds and tall beds and I have a few rhizomenous (I don't think that's an actual word) weeds that regularly work themselves up through 3' of dirt. The short 12" beds do better against those weeds because they have raspberries in them and they outcompete the weeds.

My dad has 4' tall beds and he doesn't have any weeds coming up into his beds.

Like everyone is saying the typical permaculture/garden answer is it depends.  What do you want to grow? How much material do you have. How tall do you want it, what climate are you growing in?  All info is relevant.  I can say I got a raised bed kit on clearance years ago, it was about 4" deep, and that isn't deep enough. I attached fence boards to the top making it about 12", and as others have said I can grow anything in it. That being said it's my least favorite bed.  I live in a dry, hot place, and it needs to be watered more than my other beds.
My favorite and what I call hugel beet beds. I dug 2' under ground, and two cement blocks high above ground making it about 40" deep.  They are filled hugelkulture style (large wood,soil, branches and small chunks of wood, soil, compostable stuff like leaves, kitchen waist, cardboard, stuff like that, soil, wood chips, topped with organic soil and compost.) I love these beds and will eventually convert all my inground beds.  They just outperform all the others and need less water.  
I also like the raised beds I built. I made them  about 3'  high I'm short, so it makes them so easy to use.
As far as keeping weeds out my inground beds rarely have weeds. I think I went deep enough I got most of the weeds. I know permies people will not like this, but I put down a good quality weed cloth under the cement blocks. This combination has saved me a lot of work.  I made the raised beds with hardwire cloth on the bottom so I can put it on bare ground if I want, but at this time it sits on weed cloth.
So the answer is decided what suits you best, and go for it.  Good luck.

The ideal depth for raised beds can vary based on what you're planting and the type of soil in your area. However, a general recommendation is a depth of at least 6 to 12 inches for most plants.

For root vegetables like carrots or potatoes, a deeper bed, around 12 to 18 inches or more, might be preferable to allow for adequate root growth.

If you're growing shallow-rooted plants like lettuce or herbs, a depth of 6 to 8 inches could suffice.

In essence, consider the root depth of the plants you intend to grow and aim for a raised bed depth that accommodates their needs while providing sufficient soil volume for healthy growth.

It's funny how a topic that seems like it could have one reply of, "about a foot" can have so many great examples and helpful tips in it.

Woooooooooooo!!! Friday!!!

Call me crazy, but if I'm going to go to the trouble to construct a raised garden bed, I want it up high enough to nearly eliminate bending over to tend it.  My last raised bed was constructed of 2" x 12"s and was 24" high, 2 foot wide x 6 feet long.  It served us so well that I am strongly motivated to make some more, slightly bigger.  Probably going for 2.5' x 8 feet this time.  Loading the first two thirds of the bed with punky firewood and well aged sticks from the compost area saved a ton on how much compost was needed to fill it.

Thomas Tipton wrote:Call me crazy, but if I'm going to go to the trouble to construct a raised garden bed, I want it up high enough to nearly eliminate bending over to tend it.

I actually find beds that are between 1 and 2 ft tall, harder on my back than ground level ones. That's why I went right up to the 2 1/2 ft you mention. Ground level doesn't hurt my back, but I need to limit my kneeling because of age. All our bodies are different and we all have our strengths and weaknesses. That's the beauty of permaculture - there isn't one right or wrong answer! "Observe" includes our own bodies - we need to listen to the messages they give us!

My raised beds are a foot deep, it took quite a while to fill them and I can't imagine trying to bump them all up to two foot deep with how much volume of soil I would need!

I however can sympathize with the frustration with gardening ergonomics when tending to raised beds. I'm currently using a handy dandy five gallon bucket flipped upside down as a gardening stool with mild success.

I might try to build up a tall raised bed for Hugel-shenanigans but the first step in the plan is trying to figure out a design to make said raised beds.

I'm glad this thread has resurfaced! I need to put some in, but have been struggling with the question of depth, too. As long as I'm able to sit on the ground, and have something to leverage myself back up with, ground level would be fine - but as soon as the ground is wet, I'm much less inclined! My knees and hips were sorely abused, most of my life, and now, they're returning the dubious favor. I *think* 18" - 24" should work, as long as there's enough space to move a gardening seat (with or without wheels) along, between the beds, and still have room to move my feet around for comfort. The width then becomes the question, for me: how far can I reasonably expect to reach and work across one? Or, should I simply place it and make it a width that I can reach from both sides?

I know that at 24", the bottom half would be heavy on the wood & broken down brush, that is so plentiful, here, but that still feels like a lot of soil to haul, if the beds have very much surface area.

Carla Burke wrote: I need to put some in, but have been struggling with the question of depth, too. As long as I'm able to sit on the ground, and have something to leverage myself back up with, ground level would be fine - but as soon as the ground is wet, in much less inclined!

Ergonomics will tell you, that the average human can comfortably reach 2 ft. But... but... but... What's "average"? Does body type make a difference? Does sex make a difference?  I really like to encourage people to test this sort of thing on themself.
1. A common instruction will tell you to make a bed 4 ft wide by 8 ft long, so long as it's accessible from both sides.
Reality: At ground level kneeling, females and males tend to have different centres of gravity, but body type is also a factor. Personally, I will tip over and fall on my nose if I try to reach 2 ft.
Human nature gets involved - there's always 1 weed that won't wait that's just past the centre of the bed, so I tend to reach further than I should.
However, cool thing: if I'm standing and reaching and can brace my body on the edge of a raised bed, I can reach 3 ft. So the 2 1/2 ft high beds I made (kitchen table height) can be 4 ft wide, and I can get that extra far weed, so long as I don't try to work that far out for too long.

2. Why 8 ft long? Darned if I know, but again, I think it's a human nature thing. It's hard to only work on one side of a bed. If the bed is too long, I'm more tempted to cheat rather than risk leaving things when I may run out of time/light/energy to finish a whole task. Too short, and you waste a lot of space on paths. Too long, and I am tempted to do things I shouldn't.

3. Age: As we get older, even if we're doing our best to stay in shape and flexible, we tend to take longer to heal, and our balance statistically deteriorates. If you're building beds to last, I suggest you keep that in mind.

4. Critters: So long as you protect the bottom of the bed with hardware cloth, going up can reduce issues with several ground hugging pests.

I know that at 24", the bottom half would be heavy on the wood & broken down brush, that is so plentiful, here, but that still feels like a lot of soil to haul, if the beds have very much surface area.

Absolutely - and I've done a *lot* of hauling!
1. I have some beds, that when they sank, I moved the centre dirt to the edges, and stuck duck bedding in the centre to decompose in place.
2. I did build some pallet composts quite near where I wanted raised beds. Problem is that they attracted rats, who then dug into my tomato bed. Not even sure where they got in, but rats don't need much of a gap, and they seem to like tomatoes.
3. This is the same problem I have with building hugelkulture - wood and compost are relatively light. Dirt is heavy and has to come from somewhere. Do I want a hole somewhere? Do I want to lower the ground level in my garden, so I can have relatively higher beds? I've tried that and found that it was prone to water problems in my climate. I'm really prone to having too much organic matter and no where near enough "dirt" so now I keep trying to add sprinklings of dirt any time I top up the bed, even if I can't add as much as I'd like.

Jay Angler wrote:
2. Why 8 ft long? Darned if I know, but again, I think it's a human nature thing. It's hard to only work on one side of a bed. If the bed is too long, I'm more tempted to cheat rather than risk leaving things when I may run out of time/light/energy to finish a whole task. Too short, and you waste a lot of space on paths. Too long, and I am tempted to do things I shouldn't.

I always assumed folks recommend 8 ft because that is a very common length of lumber. Try going shorter, and you have less standard options available. Go longer, and you are paying more per board foot since longer lengths are a bit harder to produce. 4x8 foot beds are an easy standard for DIY instructions because someone can buy a bunch of 8 foot boards anywhere and only have minimal cuts to make. Heck if you don't have a saw, the folks at the hardware store will probably be happy to cut them in half for you as well.

I built 2 and 3 foot hugelkulture beds. Loaded withStumps, branches, sticks,and leaves. This is  the third year with little to no problem with weeds. I love the height for my old knees. The addition to PVC pipes it is easy to cover and get plants started early.
Love reading all the different ideas!! Jo

It depends on where you are, what zone you are in, and what you wish to grow.

Zone - if you are in a desert/dry area then you could dig down to create a sunken "raised" bed that will capture water to assist plant growth.

Plant needs - if carrots and root vegetables are on the list of growies, make sure the raised bed is loose enough, deep enough and has adequate drainage for them to grow.

Mine are different depths and all seem to work fine but I have to say that the single most important concern is removing every single bit of the native plant life before building the bed. We didn’t dig deep enough and I constantly battle the tenacious wild blackberries that were near where we built. I think if I were doing it again, that I might just build my beds on concrete

Lexie Smith wrote:Mine are different depths and all seem to work fine but I have to say that the single most important concern is removing every single bit of the native plant life before building the bed. We didn’t dig deep enough and I constantly battle the tenacious wild blackberries that were near where we built. I think if I were doing it again, that I might just build my beds on concrete

I'm sorry to hear you have a Blackberry problem...and wish it was mine! I love "volunteer" blackberries!

I’m in Alabama and I’d love to share!

I find that up to 30cm is ok.....I sit on the ground to garden. If they are raised beds I have to stand and bend/stoop to garden which is worse for my back.....I try to grow without buying in stuff...so I sieve rocks from soil and make my own compost.... I'd need too much to fill beds high enough not to need to stoop...

Mostly I think it's just what works best for you. My shortest beds are 10 1/2" high, and my tallest are shy of 3', and a few in-between.  I can't say I have a favorite, or even one I dislike.  What does seem to make a difference for me is width.  Even though most will recommend 4', I like 3'.  It just works so much better for me.  Most of my beds are around 4' long because I make them with pallet wood and that is the length or the average pallets I get.  I could put a board in the center and make it 8', but 3' X 4' X what ever depth I decide is easy for me to move around and fit in the space I want.  
Basically I would say figure out what you want to grow and learn how deep the roots want to grow to be productive.  Play around with what feels comfortable for you.  Gardening can be a lot of work at certain times of the year, so you want to be as comfortable as possible.  Then figure out how much space you have for the bed, what materials your using to build the bed, and how are you going to fill the bed.   If you are going to fill it hugel style, or have a lot of natural recourses, such as compost, composted manure, organic straw... then the depth doesn't matter, but if you are going to have to buy what goes into the bed, shallow is probably better, because it can be very expensive.
I think the most important thing is just do it.  You never know what works until you do it.  Good luck

I like 18 to 24 inches or 48 inches.
18- 24 for sitting on the edge of a bed.
48 for standing at a bed.
I treat any material deeper than a foot as a reservoir for water and nutrients.
We get lots of rain, but not evenly,so the challenge is keeping it available to plants without drowning them.
In my experience leaves and woodchips should be layered above and/or below soil, but not mixed with it.

I am also interested in grow tables that sub-irragate the containers on them.
So far I've built one, ~3' high, but it needs a sump tank and pump.