[dymndgyrl]

I'm planning to convert my koi pond to a pond devoted to plants with only minnows and whichever wild critters decide to live there as fauna (otters ate all the koi). Following El Natural principles.

It is a liner pond and contains a skimmer, bottom drain and 4 external barrel filters. The sides are sloped and the bottom is bowl shaped. 17' x 16' oval and 4.5' deep in the middle.

It is in full sun, and I am in zone 8 with mild summers.

I want to cover the bottom drain (or put a standpipe in it) and put a dirt floor in - this will give me a flat surface on the bottom and also less depth (more to the liking of pond plants). Many of the plants I will still put in pots for ease of dividing and so they don't take over (lotus and waterlilies) but I would like to find something to root into the dirt bottom that is non-emergent, and perrenial.

My questions (and I would be grateful for your input, Diana) are:

How much dirt (topsoil)?
I'm hoping 1.5 ft at the deepest point would be ok, leaving me 3' of water - but 2 ft of substrate would be even better - then I could easily wade in the pond to do plant maintenance. I know in a tank that only 1" or so is recommended, so how would this translate to a larger body of water?

How much water movement (if any) and should I continue to use some or all of the filters?
I have three pumps available - a 4200gph, a 2900gph, and a 600gph. I'm guessing the bigger ones are too big (especially for lilies) and the 600 too small... and filters? I'm hoping you'll say just skip 'em.
Most water garden sites all focus on including filtration on their ponds because they all have fish to deal with (goldies or koi). But if the focus is on the plants, with only prolific and hardy minnows for fish, do I need any filtration at all?

I'll leave off for now. Thanks for any advice on this project. Here's an ariel pic of the pond.
Cheers,
Ci

 

[dwalstad]

Hello Ci,

Tricky question to answer, because this is new territory for me.

Otters, huh. This sounds interesting.

I would recommend the following:

You could leave the deep part deep. [Adding dirt to fill it up to a water depth of 3 ft deep is still pretty deep for submerged plants). Then you're going to have 1.5 ft of soil with not much growing in it. If this goes anaerobic, then you've got a real mess.] If you really want to fill up the hole, you could use sand and small rocks for your fill-in for about 2.5 ft, and then cover it with a couple inchs of soil. I did this kind of fill-in for my little pond, which was deeper than I liked.

I would add tubs with water lilies, etc to the shallow sections or add a layer of soil to the edges for emergent plants.

For sure I would try out "Floating Islands", which are floating rafts filled with emergent plants. Maryland Aquatic Nurseries (wholesale nursery) is promoting and selling them. I saw natural floating islands in South Carolina swamps, and they're really cool. If I had your pond, I wouldn't hesitate to put in several floating islands.

With all this plant growth, you shouldn't need any filtration to remove ammonia, etc. But you will almost certainly need water circulation. My little pond doesn't have any, and even though the water's only about a foot deep, it always goes anaerobic over the winter. Frogs love it, but I can't keep any fish in it.

 

[mistergreen]

yeah, you don't want to wade in to soil substrate.. it'll create a mess.
Go for pot and tub containers as suggested.

 

[dymndgyrl]

Thanks for your reply, Diana.

I am still keen on adding some kind of 'floor'. If it were planted over completely with something like sagittaria Natans (which I believe is hardy to zone 5)or elodia canadensis, that would be beautiful and provide a great environment for native aquatic critters to live in.

So you think a 1.5 - 2' base substrate of sand would not go anaerobic?

I already have various floating islands and planters in there, which were great when I had koi - really protected the plants. I would keep them, for sure. But there is alot of space in the pond, and without having to consider the needs of fish (I will only have golden minnows) I really want to take full advantage of the space for plants.

I was reading in your book (pg 130) about the idea of submerging soil for 6 weeks before planting to give it time to stabilize. Would you recommend that in my case? I can't plant till spring anyway, but I can add the substrate any time.

And one more question for now - what size pump would you put in there for water movement? (4600g pond)

Thanks again for helping me with this project.

Cheers,
Ci

 

[dymndgyrl]

yeah, you don't want to wade in to soil substrate.. it'll create a mess.
Go for pot and tub containers as suggested.

I'm hoping every inch will eventually be covered by rooted plants!

And the beauty of a (virtually) fishless pond is - if it gets murky from me or those d**nd otters or whatever - so what? It'll all settle out again and the plants won't care . . . I would have to go in to do maintenance on tubbed plants anyway - If I added pot stands they would have to go in the middle because the sides are too sloped.

 

[mistergreen]

I'm hoping every inch will eventually be covered by rooted plants!

And the beauty of a (virtually) fishless pond is - if it gets murky from me or those d**nd otters or whatever - so what? It'll all settle out again and the plants won't care . . . I would have to go in to do maintenance on tubbed plants anyway - If I added pot stands they would have to go in the middle because the sides are too sloped.

if the soil is disturbed, a lot of nutrients will be in the water column and trigger the dreaded algae.
By wading you mean walking in the pond right?
With containers, you can walk around the container and not walk on the soil.

 

[kenny1tothe6]

Very cool! I have a 50gal "El Natural" Pond and the plants grew REALLY fast! I DO live in Zone 10 Though...so that might have something to do with it. In the spring, I will be redo-ing it and making it "new"....and planting some new, better, plants. Good luck on the project! Very nice pond by the way!

 

[dymndgyrl]

if the soil is disturbed, a lot of nutrients will be in the water column and trigger the dreaded algae.
By wading you mean walking in the pond right?
With containers, you can walk around the container and not walk on the soil.

Ah, yes, point taken. I'll have to use long handled pruners or a rubber floating ring

Still, I don't see why a large pond can't be set up like a giant outdoor NPT, and I'm game to give it a try. I like the sand -on-the -bottom idea with a cap of topsoil. The soil I have in my yard is a sandy loam and has worked very well for my indoor tanks - so if I just do a few inches of that I wouldn't have to buy any - I have enough to spare.

Thanks for you kind words and enthusiasm, kenny!

 

[Diana K]

I would see a foot plus of ANY substrate as very likely to go anaerobic. I would not add that much.
6" is probably fine, and you can get the plants to root in that much, and the plants will keep it from going anaerobic as long as they are growing well. In the winter, however, most plants will go dormant, and this means little or no oxygen exchange aided by the plants. Just whatever the water movement does.

Water lilies are big plants and would really like the depth of this pond, too. Another reason for not filling it in.

However, if you really want a shallower pond I would remove the liner and fill under the liner, then replace it. That way you would have a shallower pond without that enormous mass of soil to go bad.

Planting in containers is a very good idea, to be able to remove and prune as needed, but planting directly in the substrate will allow the plants to bring oxygen down into the soil.

Substrates mix over time. I would not bother setting up a layered substrate.

How to walk in a pond that is 4' deep: build a walkway out of rock (difficult, but no chemical issues) or CMU (VERY easy, and you have all winter to get rid of the GH and KH that concrete products will introduce). Buy a wetsuit (or even a dry suit for those really cold days). Tiny boat? Maybe I am getting silly!

Drainage, filtration, and water movement: In my smaller pond (only about 250 gallons, and a hill-and-stream style) I found the substrate would go anaerobic with less than 2x the pond volume per hour of turnover. I actually ended up with over 1000 gph because I like the sound of the waterfalls.
Here is one possibility to keep the water moving through the substrate: Set up the intake using a manifold of drain pipe with LOTS of holes in it, and covered with filter cloth. This would be built in the pond so that the pipes are no farther apart than 3', and closer is better (such as a 2' spacing). Then use a pump that will give you something close to 2x your pond volume per hour. The water being pulled through the substrate will keep it aerated.

 

[Malawi]

if the soil is disturbed, a lot of nutrients will be in the water column and trigger the dreaded algae.
By wading you mean walking in the pond right?
With containers, you can walk around the container and not walk on the soil.

Another possible solution would be to place some rocks at the bottom. When working in the pond they would serve as stepping stones, while normaly beeing more or less invisible due to all the plants.

Yet another solution may be to make a collum close to the wooden patio, and use a (temporary)beam from the edge to the collum.

If a colum is undesireable, a strong beam might be used temporarily, placed parralel to the wooden patio, supporting another beam in a T shape.

BTW: The last two possibilities, are probarbly no good if the depht is more than 1.5 ft, as one would lay on the beam, and arms tend to have a limited lenght.

 

[dymndgyrl]

Thanks for all the replies, so far!

I believe that an an aggressive plant will thoroughly root the bottom if I go with a 12" to 18" layer of soil, and this will keep the soil aerobic. It would be very much like a root bound plant in a large pot. Just alot of them. In a really wide pot

On a ponding forum, I got a recommendation to plant spiral valisnaria on the bottom - it seems to be quite hardy, the person has it in a mud bottom pond in zone 6b.

Like I said before - I would keep my lotus and lilies in pots for dividing purposes, and marginals in my floating planters (there are no shelves in the pond) - but I think i will try for the "lawn" on a dirt bottom idea. I'll keep you posted about how it's working out.

I also got an idea from someone to fish out a bucket or two of water and mud from a local natural pond to "seed" the pond with native critters. They said you would be surprised and amazed at what will start appearing in the water if you do this! Can't wait till Spring . . .

Cheers,
Cindy