The cheapest material you can get is sandy fill soil from a landscape supply place delivered in bulk. I think around me it's $24/cuyd.

I fill the bottoms of my overlarge deck plant pots with plastic milk jugs or overturned plant pots and plastic buckets. Soil fills any gaps and my containers are lighter. Last year---I don't remember my theory now---I filled the bottom of the planters with soft, rotting logs. My plant roots do not approach the fillers I use.

Annpat's soft rotting logs are a good idea - sort of a bastardized hugelkultur. It wouldn't have to be rotting either, just dead wood.

Assuming that the bed is in direct contact with ground: You can fill with any material to take up space. But as you build it up make sure the gaps are filled with a soil similar to what you are eventually going to use on top. It can be a bit coarser though not much different - eg soil mixed with some half inch gravel. Make sure to fill the gaps between whatever logs/bottles you use. This way the soil at the top will have a similar path to the bottom and will aid in drainage. This is sort of the same as Al's ballast idea. What you do not want is anything that will decompose fast since the soil above will start sinking and you will to keep adding soil frequently.

That deep is completely unnecessary. I agree that if you need that deep a configuration for other than horticultural reasons, get some used quart size pop bottles as filler.

For a normal raised bed garden those dollar a bag “topsoil “ bags they sell at the big box stores works fine, although they aren’t really topsoil.

Yeah, at some point it becomes cheaper to buy in bulk from the landscaping place.

1. It is much better to do the hügelkultur method rather than non-organic filler. I have 1 to 5 year old high beds because I'm unable to bend down to normal height beds. Require's adding about 3" once per year to refill beds but often just use another year without topping off. Water required is cut at least 75% compared to inground planting.

I should have mentioned that the containers I fill the bottom of with milk gallons are large, annual planters. I empty them each fall. I wouldn't use plastic fillers otherwise. My largest planters are on my upper deck and I don't want a lot of weight up there, nor do I need 24" of soil depth for marigolds or whatever.

I have to echo the concerns about raising beds that high. When you do that you no longer have an organic garden bed - you are creating a container environment.

The primary concept behind raised beds is to simply raise the existing soil level by adding amendments (like compost and manure) and turning the soil to add air. You need the existing dirt because that is where the life is - fungus, bacteria, beetles, worms, etc., and also minerals. They won't be there in an artificial container soil. Actually, a wood pallet which is usually 6.4" tall is ideal. This whole thing may be a lot easier than you imagine.

Thanks to all. Many good ideas here. I need them 3-4 ft. tall because I developed a bad back. I am reluctant to use plastic bottles as filler because I am concerned that thier gradual breakdown might leave some unfriendly chemicals in the soil. The hugekultur method is fascinating. Thanks for bringing it to my attention. Using wood chips sounds similar. I have access to a large supply of well aged ones. I'll let you all know how it goes at the end of the season.

Yes, hugelkultur sounds great. Proponents recommend large chunks or logs of wood rather than chips, because the chips having more surface area may demand more nitrogen. But if you have access to well aged wood chips, that would be the greatest filler for your high raised beds. They'd likely shrink down year by year so you'd have to add a little more soil or material every year, but as long as you don't mix the wood chips up into the topsoil you'd likely develop a very excellent bed after a year or two, and it would be long-lasting.

Hugelkulture is unscientific nonsense. The logs will tie up nitrogen and cause a perched water table above the log layer.

I won't debate the benefits of hugelkulture here, although there are some bad assumptions in the above statements.

Just wanted to say that wood chips will decompose and shrink, so expect to have to refill your beds every year as they decompose!

Neither will I Tox but saying logs are impermeable to water isn't only "unscientific nonsense", it's uneducated hogwash.

Very interesting post and responses. I usually plant in the ground in my half acre garden, but my tractor and tiller went down last Spring and I am working this year so I'm going to containers for this season. I have a lot of seasoned firewood stocked up for next winter so think I might use a bit as a shallow filler in some of my tubs for veggies that don't require so much depth. Thanks.

Madonna

Madonna, containers are completely different from a raised bed scenario! And there is a very good reason why the material filling a container is different both in substance from a raised bed soil as well as needing to be uniform in consistency throughout. So no firewood in the bottom :-)

We've spent this spring converting all of my gardening beds to accessible raised beds that are higher. After much thought and research, we decided to go ahead and make them SIP beds to reduce everyday watering needs that would require more work from me. (Less bending, lifting watering cans, wrangling the hose, etc.) You might not want to do this, but just thought I would throw the idea out if you want to give it a go before filling your beds with planting media. My favorite filler is made of equal parts coco coir, perlite, and compost. The perlite keeps it lighter and leaves important air pockets for the roots. Coco coir is the perfect replacement for peat moss; it holds moisture well and is an easily renewable resource. Both are cost effective if you shop around. Good luck with your garden!

For the less informed, can you explain what an SIP bed is?

Sub-Irrigated Planter

I thought it might be a hammock where one relaxes to SIP barley pop.

I was thinking Stooping Is Painful but I like yours better klem.

Thanks GG.

Uneducated eh Klem? I'm a landscape architect with over 20 years experience actually writing specifications for soil profiles and quite a bit of education on the subject. I never said it was "impermeable" just that water would perch above it. This is a well documented scientific fact. If you have a textural change in soil, water will perch above it until saturated and then drain. It's just like putting rocks in the bottom of a pot or having a sand layer under a layer of soil in a field. I'll see if I can track down the educational video that's only about 60 years old showing what happens to water when it hits a patch of crop residue (best analogue for hugelkulture since scientists tend to understand burying a bunch of wood in your veg garden is a bad idea) in the soil profile.

Here's the video on water movement through soil. The example of an organic matter layer, in this case straw but it could be anything, starts at 20:30. https://m.youtube.com/watch?v=DmTNFIEc2VA

Nil13: i am not a fan of hugelkutur but whether burying logs will cause PWT to be raised depends on how densely it is packed. If there are sufficient space between logs filled with similar soil as above then it will not have much effect on PWT. Effective depth of the soil will be influenced by the soil in between the logs or other filler materials. On the other hand if they are packed tightly covering a large surface area without much soil filled path to the bottom then it will definitely raise the PWT and allow the upper soil layers to be saturated. It could be argued that having even a few logs will slow down the effective movement of water downwards and thus allow the soil above to remain saturated for longer periods of time.

Nice illustration in the video you linked. Thanks Nil13

TOC, If the soil surrounds the log then the only perching will occur directly over the log just like if it were hardpan or a big rock. However, the buried log will still tie up nitrogen and, unless you have pure sand, have less water holding capacity than topsoil.

Hugelkulture isn't just burying a log however. The construction involves many different layers of organic material piled up on each other.

I thought the log rotted, absorbed water like a sponge, and roots found their way in to get water during dry periods. Isn't water retention part of what makes it work?

How much N can a piece of wood absorb, and from how far beyond its surface? If buried as deeply as recommended, isn't that pretty much below the elevation where all the nitrogen action is happening anyway? It can't suck nitrogen from a foot or two above it, can it? Maybe it does.

It only absorbs water like a sponge when it has rotted and voids have opened up in the cellulose and it has been colonized by mycelia. That can take years depending on climate.

No, the logs won't suck nitrogen from 2' above it. It will just lockup nitrogen in the surrounding soil.

The catch is that if there is enough oxygen for the fungus and bacteria to decompose the log, there is enough oxygen for the roots to colonize that deeply into the soil. If there isn't enough oxygen, you are setting yourself up for anaerobic decomposition and the production of hydrogen sulfide which you definitely don't want.BBut that is specific to this one case. Hugelkulture only calls for an inch of soil over all the different layers.

You are a lot better off just chipping those logs and using it as mulch.

I do not like Hugelkulture, IMHO it is a waste of good wood, but that is my thing, you have the right to do your thing.

I agree that 12" is most for a good garden, but Robert Rodale(old school organics) OGM book

"Getting the Most from Your Garden". He said carrots,cabbage, pepper, tomato root can go 60 inches deep, that's 5 feet.

I double dug all my beds, but do not build a fence & fill it, I use the ground, the old school way.

Another way is to cut/dug a trench & fill it with organic waste, then plant beside the trench.

This is not my ideal, it is from:

https://www.redwormcomposting.com/large-scale-vermicomposting/the-vermicomposting-trench/

Corrected on using logs. Am using all soil and everything planted so far is doing well.

I use empty, capped water bottles 16oz or so) in my self watering containers. Seems to work so far.

Why have a 36-48 inch high bed, if you are not using all that room?

I understand the jugs in containers, plant look nice in big clay pots, but they are heavy.

The jugs lighten the pot, with out harming the plant.

But you do not pick the raised bed up & move it.