How deep should a grow bed be?

[HealerOliver]

I have found a source for my grow beds. This fiberglass company will make them just about any size I want. So, my question is; for an 1 square meter grow bed, how deep should it be?

Oliver

[GaryD]

Hi,

Grow beds can be any depth from 150mm to 300mm (6" to 12"). They can be even deeper but they'll cost more to make and they won't work any better.

The argument in favour of 150mm grow beds over say 300mm ones is that they require less media which, depending on your choice of media, means half as much work to fill them and/or half the cost to buy the media.

Conversely, you can have twice much growing surface for the same amount of media/expense.

My grow beds are 300mm and 350mm deep respectively.....because that was what was available.

Gary

[Murray]

Another view in favour of 300mm (1 foot) deep grow beds is that it works much better with deep rooted veggies such as tomatoes and corn. The shallower grow beds are fine for such things as lettuce etc.
Also, by employing deeper grow beds there is just more volume of everything which tends to add more stability to any system.

[Dufflight]

How big is your fish tank. In my larger system I use very deep GB's to increase the amount of media for the bacteria. On smaller FT's you may not need this. Think mine range from 40 to 70cm.

[Outbackozzie]

I have beds up to 1m deep, which increase the temp stability greatly.

I'd say 300mm is the minimum for corn and tomatoes etc. Even then they fall out of hydroton :rolleyes:

[GaryD]

Hi,

If you'd like to see a wide range of vegetables and herbs (including tomatoes and corn) growing in 150mm deep beds......click here (http://www.aquaponics.com.au/aquaponics_videos.htm).

Gary

[Outbackozzie]

Yes, I grew them all in under 75mm of media as well - but it is undeniably better to have more depth.

[GaryD]

Hi OBO,



.....but it is undeniably better to have more depth.

I sense that's the feeling some quarters but are the reasons so compelling that you'd want to pay much for deeper ones if you were starting from scratch.

If you have sufficient nitrification to cater for the size tank that you have and you are able to effectively control the environmental conditions to which your system subject then I contend that it doesn't much matter.

Fibreglass is costed (in large part) by the weight of the materials that go into the particular object that is being manufactured and, if you're using anything but gravel, being able to get away with half of the media is a further significant saving.

The 300mm thing is one of those "guidelines" that someone suggested early in the piece and (like many other things around aquaponics) it's been accepted without much question.

The fact is that tomatoes will grow happily in no media and corn is a plant (like root crops) that wouldn't survive a cost benefit analysis as an AP proposition. Just about everything else will grow in 150mm of media.

Some of the other benefits of 150mm grow beds include portability (important for those who rent their homes) and ease of maintenance and cleaning.......and despite what people currently think, all growbeds will require cleaning sooner or later.

Gary

[Dufflight]

Wouldn't it be cheaper to get one 1m X 1m X 600mm
than two 1m X 1m X 300mm because you only have to pay for one bottom. Think it depends on space and FT volume. If you only had room for a small gb but need more media for bacteria then deeper is the way to go. Just another variable.

[Outbackozzie]

Points taken Gary :D

[Murray]

Cleaning of the grow beds is really not an issue....mine are now 3 years old and doing fine.
Any garden bed system will need maintenance - re digging or whatever....but a garden bed system that will go three years (possibly twice that) without re digging or cleaning out has got to be a winner.
Even if I did have to clean the beds out once every three years, I would reckon I am on a winner.
300mm or deeper grow beds are proven to work well. Every day the track record for 300mm or deeper grow beds gets better and better.

Yesterday I pulled the strawberry's out and replanted one half of the bed with corn. The other half of the bed I direct seeded with cabbage and some lettuce.
Those strawberries have been in that bed for 2 seasons. The year before that it had a variety of plantings including tomatoes. Last year there was a resident Grosse Lisse tomato vine that got so big it blocked out the sun to the bed below that resulted in a diminished strawberry harvest. I cut the tomato vine down when it had been bearing for 9 months, and only then because I renewed the greenhouse.

The roots of the removed strawberries had some whopper worms in amongst them.

The small Jades had a party !!!! One would get the worm and it would be trailing out of its mouth way past its own body length as it made an escape with the prize....other Jades in hot pursuit snapping bits off the worm....nature at work is a bit cruel.

Recycling of nutrients at it's best !!!!!

A wonderful, nutrient rich, mature grow bed...fish poo, worms and all that other stuff that we can only imagine, that goes to make up a great gardening concept.

[GaryD]

Hi Murray,



300mm or deeper grow beds are proven to work well.

I agree absolutely.....but the original question was from Oliver who was able to get his beds made from scratch and he wanted to know how deep they should be.

As I've demonstrated, they can be any depth from 150mm upwards and that there are benefits in having 150mm ones......cheaper, easier to clean and move......and much less expensive to fill.

My (your) 300mm growbeds work beautifully but I'd be just as happy to have bought shallower ones had they been available. Another product line perhaps?

Gary

[Murray]

Another product line perhaps?

Yes indeed . I am about to re do the moulds for our original 585 ltr grow bed.
We have now made just a few over 500 of those now and the moulds are very tired.

During that process I intend to make a couple of new sizes and a shallower grow bed offering will be in that mix.

It will be interesting to see just how many are taken up by AP people.

[HealerOliver]

Thanks all for your replies.

Perhaps a better question would be, how much bio-filter do I need? The reason is this: I am following the rule of 1 to 1. That is, the fish tank water volume is the same as the total grow bed volumes combined.

Inasmuch as the bio-filter is the grow beds (using clay popcorn) then does it matter if I double the grow area and half the depth? This would allow for more veggies, but then I would need more fish poo and therefore more bio-filter and deeper grow beds. That would then change the 1 to 1 ratio to 1 to 2, but I'd be back to 12 (~300 Mmm) inch deep grow beds again.

I can see from my research (this is part of it) that there is a lot of grey area here. Unless I can see a safe reason for reducing my GB depth and therefore the bio-filter mass, I will go with the 12 inch deep GBs.

Oliver

[Murray]

There is a bit of grey area here, but all I can tell you is that 300mm deep really works. Mine are 3 years old and going strong. Others have been doing this longer than me and have had consistent results with 300mm or deeper grow beds.
If you want to go to 150mm deep I am sure it will work, maybe not just as well or maybe as well. I don't know....but why introduce an unknown into a new project ? Why not do the proven way....then experiment later when you have some experience behind you ?
Look through this forum and others and see just how many shallow grow bed systems you can find....not too many ! (if any) You will find some wacky video clips on you tube doing it all sorts of weird getups. Surley no one who seriously wants to produce fish and veggies for their family would waste good money and time on some of the wacky ideas seen on you tube ???
I am sure the cleaning issue will come up a lot sooner in a shallower grow bed.
The 1:1 ratio is also not a hard and fast rule. It is just a fairly reliable guide. Established systems with a good fish stock density can easily run double that.

What you should be more concerned with is the stability of your system.
Stability in temperature, pH, and general water quality increases with more volume in the total system.

I am sure that you can have enough shallow grow beds to be effective bio filters for your system, but for me I see so many proven advantages for the deeper grow beds.
They have a track record of consistent good results.
The only possible logical reason to have shallower grow beds is the saving in media cost....and that would be a real consideration if purchasing expensive but good clay pebbles.
There is only one web site that I have seen that advocates shallow grow beds. That website has lately taken on 300mm deep grow beds to sell and dropped the shallow ones off their sales site.

[Dufflight]

300mm is a good minimum size. At least with a deep GB you can fill it to a lower level and add more media later. You will have to adjust the siphon level. When I first started filling my 1000ltr GB with gravel I got half way and put in a lower siphon. When I got more motivated I finished filling it and adjusted the siphon for the higher level.:D

[GaryD]

Hi,



The 1:1 ratio is also not a hard and fast rule. It is just a fairly reliable guide.

I can remember that it was not so long ago that the recommended ratio was 2:1......and then someone thought to challenge it and it became 1:1. The fact is that, without qualification, it means nothing and is next to useless. The origins of the 300mm grow bed depth are the same.



.....but for me I see so many proven advantages for the deeper grow beds.


And they are....? No one's arguing that 300mm grow beds don't work. I'm simply demonstrating that there is no tangible evidence to suggest that 150mm beds would be any less effective and that, in fact, they do have some advantages of their own.



You will find some wacky video clips on you tube doing it all sorts of weird getups. Surley no one who seriously wants to produce fish and veggies for their family would waste good money and time on some of the wacky ideas seen on you tube ???

The You-Tube video that I referenced that features shallow beds was produced by people who have more experience of aquaponics than anyone on this forum. They operate seven AP systems, most of which feature shallow beds.

The only possible logical reason to have shallower grow beds is the saving in media cost....and that would be a real consideration if purchasing expensive but good clay pebbles.
Let's not forget lighter weight, portability, ease of maintenance/cleaning and the upfront capital cost of the beds. Using shallow beds also provides a greater growing surface area for a given quantity of media.


What you should be more concerned with is the stability of your system. Stability in temperature, pH, and general water quality increases with more volume in the total system.

An 8' x 4' grow bed that is 150mm deep contains the same amount of media as a 4' x 4' grow bed that is 300mm deep....and, since it contains the same mass, it is just as stable as the deeper one......but it also offers twice the growing area.


There is only one web site that I have seen that advocates shallow grow beds.
Not quite! They are widely used in the US and I advocate their use......for all of the reasons that I've suggested. The same shallow beds are also widely used in hydroponics where they do the same job as they do in aquaponics.....namely to grow plants.

Gary

[Murray]

Evidently we are in agreement Gary, 300mm deep grow beds are great. That's good to hear.
A wonderful well proven system that works very well.

[GaryD]

Hi Murray,

Not quite what I said.....but I understand that you've probably exhausted your arguments, so ignoring the rest of what I said is probably the most comfortable route.

Gary

[Murray]

There is really no argument, and it is true, I am very comfortable.... thanks.
I are enjoying wonderful flow of business at the moment with hundreds and of grow beds and kits out there.
I have some new products for release in the new year, and the DVD is going out at a good rate, many more than I expected.
Thanks to all that have purchased our products in 08.

Have a happy Christmas and a prosperous New Year.

[Dufflight]

I can see how a 150mm Gb might be handy but mainly as a side GB. Like when running vermiculite it is easier as a controlled side GB because it has different water requirements. Also media would make a difference. Gravel would not move around but clay does seem to give a little when on a flood and drain cycle. How does the bacteria go with out as much darkness. And the temperature would fluxuate in the plants root zone so having the GB in full sun could effect some plants. Might be interesting to trial one and see the pro and cons.

[fishfood]

Best i chime in on this one i have 9 grow beds ranging from 100 mm to500mm they have different media in them they all flood and drain they all grow well [no difference] In my book what ever you can afford and is available is the right one you will find as the system gets established the root ball on the plants gets smaller because the nuetrient is taken to the plant it doesent have to search for it

[Dufflight]

Are you able to run the shallower GB because your system is older and more stable. Or did you have the 100mm ones in from the start.

[fishfood]

Are you able to run the shallower GB because your system is older and more stable. Or did you have the 100mm ones in from the start.
I would say yes to both of those

[damien little]

Just a quick point. 2 growbeds 150mm deep but twice the surface area of one at 300 mmm deep will not offer the same biofiltration unless you are flooding both growbeds to the surface. As you are aware, if the media is not getting wet, it ain't doing a thing with regards to biofiltration. We flood to about an inch below the surface, so for this example, the 300 mm deep bed would have 72 litres less medium being effective as biofiltration. Now, at 35 bucks a bag, that's about 50 bucks worth of media wasted in the shallow growbeds, albeit that there is twice the surface area. never an argument that could be awarded a winner, just one of personal preference imho. Personally, I would never go less than 300mm, mainly because with the growbeds in full sun , in summer the shallow beds will cook imho.