Feed your DIRT

First let me nearly disqualify myself as I do not have a dirt tank. My 60g is a somewhat sterile canvas with a gravel/sand substrate and (dare I say it) plastic plants (although I do have real rocks!).

I have however been involved in organic gardening for over 30 years. In so doing, I have made tons of compost and have even made truckloads of vermicompost (composting with redworms).

In order to produce healthy plants, fruits and vegetables, you have to FEED THE SOIL. There is an incredible ecology that happens in the soil in order to breakdown organic matter into plant usable nutrients.

So your starting out with nutrient rich organic potting soil, perhaps augmented by some clay and/or other additives. After a bunch of water changes and filtration and a bunch of plants, things are looking good. Assuming decent lighting and water quality, the plants should be growing really well...but unless you take measures, things will level off and in time, plants will not grow so well. Now here's where some will be tempted to start using petro-chemical fertilizers in liquid or root tab forms. Well, if you were gonna end up doint that, you might as well not started with dirt at all - just used sand/gravel and done hydroponics!

If you have a dirt tank, you need to FEED THE SOIL and develop the ecosystem. In so doing, we'll borrow a couple of ideas from the 'deep sand bed' folks.

First, your soil needs a constant supply of organic matter so to decay and feed your soil. So put that gravel siphon down and leave the mulm alone. A layer of decaying mulm is essential in maintaining the health of your aquatic soil. If you want a cleaner look, say in front, slosh the mulm towards the more heavily planted rear of the tank rather than removing it. Of course you can do some cleanup, but try to keep as much organic waste as possible that will feed your subsoil...and ultimately feed your plants.

If you don't have sufficient stock, you still need to find a way to organically enrich the soil - perhaps by adding fish food for invisible fish ;-)

Consider adding some subsoil life. California black worms are the aquatic equivalent to redworms. They will burrow and aerate the soil, process decaying organic matter and their castings are pure organic gold in the substrate.They will also make a most excellent supplemental food source for your fish.

Malaysian Trumpet Snails will burrow in the top inch of gravel/sand keeping it aerated. This assists the bacteria that lives there and breaks down organic matter further.

I could go on and on here, but don't want to 'preach to the choir' or wear out my welcome. I'm very interested in the soil substrate aquarium and will start one when I have the space and time. I wrote this because I've learned alot about good growing soils and what I've seen so far regarding the 'dirt tank' doesn't seem to address long term organic maintenance of the subsoil, so I thought I'd toss this out as food for thought.

If you got this far, thanks for reading - hope you saw some value in it.

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Permalink Reply by Hmoobthor on November 16, 2011 at 12:15pm

thanks for the info...

people who keeps plants would know this too

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Permalink Reply by Michael V on November 16, 2011 at 3:00pm

I'm sure there are many people that 'know' this ... but we live in a fast food, throw away, petro-chemical world. If you were to ask a bunch of people how to feed plants, the resounding answer would likely be "fertilizer", rather than "compost".

In my rummaging around here in the dirt tank world, I haven't seen much about biotope or much of anything about organically fertilizing the soil bed. So maybe everybody knows and nobody talks about it???

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Permalink Reply by Jason DuBois on November 24, 2011 at 1:37am

I read a book that suggested dried rabbit poop down close to the roots to feed the plants/soil. what do you think about that?

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Permalink Reply by Michael V on December 2, 2011 at 4:46pm

Rabbit poo is good stuff, but it may very well want to float. I would opt for the more natural fertilizer in the planted tank.

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Permalink Reply by Jarrett Hunt on November 25, 2011 at 7:32am

If you have more to say about the subject please say so. I'm really interested now. If I take the clipping from one aquarium and put in on the bottom of a newly dirted tank about how long will that last? I thought about this 3 days ago when I had tons of hygrophilia leaves being tossed. I decided against it because I heard that too much organics in dirt is bad.

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Permalink Reply by Michael V on December 2, 2011 at 5:14pm

Some folks are prolly too quick to keep the tank clean. In the natural planted tank, you really do want a good layer of mulm to be constantly decomposing on/in the substrate.

Think of the forest. Take a shovel into any deciduous woods and turn over some soil. Dark, rich top soil - naturally. The leaves come down in the fall and slowly decompose. All sorts of critters in the soil food web convert that organic matter into rich humus and plant usable nutrients.

In the planted tank, fish waste, uneaten food and plant waste = mulm. A decent layer of mulm will break down and feed the 'dirt' substrate ... and consequently the plants.

If you don't allow this to happen, the nutrient rich soil you started with will become depleted as your plants use them up. In time, you're not much better off than if you'd used a sand only substrate.

So think of your dirt tank as a natural eco-system. Let the mulm decompose. Add a handful of malaysian trumpet snails and some California black worms to help in the decomposition and to keep the upper substrate aerated.

Now all things in moderation. You may want a section in front to be very clean for appearance sake...and that's okay. But let the mulm mulch and decompose in the rear where your taller plants are - they'll likely need more 'fertilizer' anyway.

The key here is like the forest, you need to be patient and let the material break down in the upper layers of the substrate. You don't want to bury organic matter too deep as anaerobic decomp of organic material can produce some ugly gases. However, if allowed to decompose aerobically, all will be good.

There is no good way to predict how long it will take to decompose a layer of mulm on the bottom of your dirt tank. It will be an ongoing process. I can say that you could have an inch of material in spots in process of decay and there is no problem with this other than appearance. As a matter of fact, you might want to research deep sand beds. Deep sand bed approaches began with SW and then migrated to FW tanks. Dirt tanks are pretty much the same with top soil down under, more closely emulating nature.

We're really just talking about organic gardening under water.

:-)

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Permalink Reply by Jarrett Hunt on December 3, 2011 at 9:02am

So I should mix in leaf clippings near the surface of the soil before capping it rather than the bottom to prevent bad gases?

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Permalink Reply by Michael V on December 4, 2011 at 11:32am

If you're determined to add leaf clippings, then yes...but they'd need to be ground up into tiny particles and put between the dirt and sand, but they're gonna want to float. I wouldn't bother. I honestly think we're better off starting out with just regular old (organic) top soil * or mineralized top soil.

By organic top soil I mean sifted garden top soil that has not seen petro-chemical fertilizers and pesticides. Mineralized top soil takes organic top soil and 'burns off' organic matter. I don't think we want a lot of organic material breaking down when we fist start a 'dirt' tank and we surely don't want organic material decomposing deep in the substrate. What we really want and need are the minerals and trace elements only found in dirt since sand is so sterile.

When I referred to 'feeding the dirt' I was more referring to the long term maintenance of the soil substrate. To let the biotope ecosystem process the mulm (fish and plant waste, excess food) and convert it into plant usable nutrients.

Any filtration inlets (if they exist) should be high and returns designed not to stir things up too much to attempt to capture detritus.

In theory, a well managed dirt tank, like a well managed organic garden, should last forever and produce some really nice plants with little/no petro-chemical intervention.

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Permalink Reply by Michael V on December 4, 2011 at 1:02pm

Thinking about this more, I think a layer of fine compost or vermicompost between the soil and the sand would be best. The idea here is organic matter that has already been decomposed - not quite humus, but close. This would also set the stage for some fine food for the California Black worms.

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Permalink Reply by Martin on December 13, 2011 at 2:02am

Your comments were very helpful and made a lot of sense thanks I will stick to your advice I like the black worm idea

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Permalink Reply by Vince on December 2, 2011 at 5:15pm

Great post!

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Permalink Reply by Michael V on December 4, 2011 at 1:25pm

Thanks guys! I was afraid it might be one of those 'tell us something we didn't already know' posts.

You know I was also thinking. What's the deal with these instructions that call for 1" of soil covered with 1" of sand. If I was to put an inch of soil and an inch of sand on top of concrete, what do you think would grow there? Maybe some grass, but not much else. I'm sure a lot of plants like amazon swords need more than 2" of 'soil'. So lets at least think about deeper beds. Oh I know, chicken little ran around and scared everybody saying deep beds were dangerous because of that evil anaerobic bacteria.

Well, anaerobic bacteria is in there, so get over it. Man up and make that bed deeper. Just don't push fresh organic matter deep into the substrate and everything will be fine. This will be something to remember when you're doing your 'gardening', moving stuff around and planting.

So how deep? Well, just my $.02, but I think we want about 2-3" of soil and 1-2" of sand...and of course, we might want it deeper in the rear than the front and perhaps some contour side to side. Maybe a hump of sorts in the middle - just more interest than flat lands.

I think the hardest part about a dirt tank is the patience. The setup and the subsequent days of water changes and filtration to get things settled. I'd also plant and let things settle and get established before adding fish. I'd say 2-3 weeks (or more)...and this may sound nuts, but I'd add a pinch or two of good fish food once or twice everyday during this period to feed the invisible critters in your emerging biotope.

Thanks for reading these ramblings. May your aqua garden grow!