# Cold Tolerance of Aquatic plants



## Z1234 (Oct 25, 2016)

Hi,

I have an outdoor 80 liter (~20 gal) tank that I cannot heat and water started to freeze.










Do you know how cold water can the following species tolerate?

Vallisneria
Bacopa Monnieri
Bacopa Caroliniana
Elodea Densa
Cabomba

The tank has made it through half of the winter so far, but when water temperatures started to be below 5 degrees celsius for weeks, the plants started to take a beating, but no disaster yet.

Is there any chance it will make it to the spring?


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## Michael (Jul 20, 2010)

Several of the genera and species you list are native to SE North America, so they should survive the winter if planted in a pond. I grow _Bacopa caroliniana_ and vallisneria in my ponds here in USDA cold hardiness zone 8.

But a pond is different than an outdoor aquarium. Water temperature in a pond is moderated by the latent heat of the soil. I assume your aquarium is on some kind of stand. This, and the small volume of water, will allow the temperature to fluctuate a lot more, and become colder. If the water surface in the aquarium freezes solid, the pressure of the expanding ice could easily break the glass, or at least pop the corner seals.

Where do you live? A lot depends on your local climate.


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## Z1234 (Oct 25, 2016)

Michael said:


> Where do you live? A lot depends on your local climate.


I live in Europe, continental climate.

Based on the link below, I am in zone 6.

https://www.gardenia.net/guide/european-hardiness-zones

None of the plants mentioned above are native here (as far as I know).

Occasionally I put 5 liters of hot water into the tank to prevent water from freezing too badly.

How does your pond vallisneria and bacopa caroliniana tolerate less light during the winter? Does the surface of the pond freeze?


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## Michael (Jul 20, 2010)

We recently had low air temperatures of 18F/-8C and water temperature in the ponds fell to 40F/4C. The plants become dormant and do not grow at these temperatures, so light levels are not very important. Winter weather here is often sunny, so there is still enough light for photosynthesis.

The water surface in my ponds would freeze if I did not keep the recirculating pumps running during the winter.


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## Z1234 (Oct 25, 2016)

Michael said:


> We recently had low air temperatures of 18F/-8C and water temperature in the ponds fell to 40F/4C. The plants become dormant and do not grow at these temperatures, so light levels are not very important. Winter weather here is often sunny, so there is still enough light for photosynthesis.
> 
> The water surface in my ponds would freeze if I did not keep the recirculating pumps running during the winter.


Thanks, based on this I will keep the tank and see if it makes it to the spring. It might not be as hopeless as I thought.


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## dwalstad (Apr 14, 2006)

You are exposing a lot of tropical plants (e.g., Cabomba) to some very tough conditions. Come spring, the tank might contain a lot of dead plant matter and debris. 

In my pond, I routinely do a big spring cleanup to remove all the debris. Otherwise, the pond substrate goes severely anaerobic and the frogs die.


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## Michael (Jul 20, 2010)

My big problem with anaerobic conditions in the ponds is decaying fallen tree leaves. I try to do a cleanup right after all the leaves have fallen so that the fish do not spend the winter in anaerobic conditions at the bottom of the pond. Right now the cleanup is overdue!


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## Z1234 (Oct 25, 2016)

Thank you everyone for the input. I'll see what happens and keep on cleaning the tank as necessary. Of course there are no animals in it, except a few pond snails, that hijacked their way in. They are doing fine.

It surprised me how well some of the plants tolerated cold weather. Originally I thought when temperatures go below 10 C (50F) the tank would be gone. That was 1-2 months ago;


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## dwalstad (Apr 14, 2006)

Michael said:


> My big problem with anaerobic conditions in the ponds is decaying fallen tree leaves. I try to do a cleanup right after all the leaves have fallen so that the fish do not spend the winter in anaerobic conditions at the bottom of the pond. Right now the cleanup is overdue!


You're absolutely right. I have a wire netting cover to keep leaves out, but they still get in. I have been scooping out the leaves all during the fall every week or so. If I waited til spring, the pond would be in truly sad shape. 

I used to have only tropical plants in the pond, which always got killed by the winter cold. A nice person from the aquarium club gave me some native frogbit. That plant and some other Sagittaria collected in North Carolina waterways do well in the pond year after year.


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## Z1234 (Oct 25, 2016)

Thank you for the advice. For next year, I'll do my homework and study where the plants are native and select based on that.


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## Z1234 (Oct 25, 2016)

Because (I think) my outdoor tank was so successful last year, I've also started one this year.

After planting:










I know, far from ideal starting conditions. Plants in bad condition and just not enough. But this is what I had to cook with.

After start, an _unexpected _cold front hit the tank and water went below 5 Degrees Celsius.  This is no good, but I think as long as water temperatures are above 10 C, these plants do fine. (Pistia may have trouble...)

After 2 months the tank fully recovered:










Nicely grew in at mid summer. Algae is usually not a problem at all even though the occasional direct sunlight. On this picture there is a little bit of brown algae which came after I did a water change with tap water and no treatment. I guess the chlor/chloramine nuked the biofilms/bacteria and this gave a bit of opportunity for the diatoms to spread. I think it will quickly go away.

Inhabitants: a few endler guppy and a few Red Cherry Shrimp (only when temperature range allows)

I found that the Walstad method works very well for outdoor aquariums, where using equipment is difficult (no electricity...). In my climate the temperatures are reasonably OK between (end of) May to Sept/Oct.

I usually don't put fish in because I am not sure about their temperature tolerance. This tank is 200 liters, so the daily temperature fluctuation is not as high as with much smaller tanks.

My plan is that I disassemble the tank and give away the plants in September/October.


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## Michael (Jul 20, 2010)

Looks good, thanks for the update. This gives people in subtropical and mild temperate climates another way to enjoy planted aquaria.


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## dwalstad (Apr 14, 2006)

Z1234- Nice Tank! The plants have really grown well for you. I love the water lilies.

Christel Kasselmann's _Aquarium Plants_ (2003) has a table in the back (pp 478-481) for temperature tolerance of aquatic plants. It seems quite a few of them can go down to 4C: _Alternanthera reineckii, Echinodorus berteroi, Hygrophila polysperma, Ludwigia repens, Vallisneria spiralis_, etc. _Pistia stratoides_ goes to 15C.

In my own pond, _Limnobium spongia_ and _Sagittaria graminea_ survived winter even with thick ice layer.

Now that I'm raising guppies, I set up some outdoor containers on the deck. (The clear plastic one--a treasure--was designed for storing sweaters. It holds 18 gal, cost $8 from the hardware store, and has a lid.) The first night a frog laid 100s of eggs in the 20 gal tank. I tossed most of the tadpoles, but saved a few for each container. You can see one of them with the guppies. I think they have a calming effect on the fish. Plants and fish seem to thrive outside.

I'm planning to extend the season as much as possible, hopefully into October. I'll cover the containers with a large, clear plastic sheet and run a heater for a few hours on cold nights. All the containers hold about 15-20 gals, so they'll hold enough heat for fish/plants if the water's warm enough (80-85 F) in the evening and kept covered at night.

Here are few photos of my 4 containers. The blue one is an old horse muck bucket that was lying around in the shed.


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## Z1234 (Oct 25, 2016)

dwalstad said:


> Z1234- Nice Tank! The plants have really grown well for you. I love the water lilies.
> 
> Christel Kasselmann's _Aquarium Plants_ (2003) has a table in the back (pp 478-481) for temperature tolerance of aquatic plants. It seems quite a few of them can go down to 4C: _Alternanthera reineckii, Echinodorus berteroi, Hygrophila polysperma, Ludwigia repens, Vallisneria spiralis_, etc. _Pistia stratoides_ goes to 15C.
> 
> ...


Thank you for raising my attention on the book with the temperature tolerance table. It helps to "calibrate" my "expectations".

Based on what I saw with a few plants last year in my outdoor tank, probably "max" and "min" values in the table are a bit conservative, meaning if temperature goes out of the range for a short period of time only (i.e night, or a few days), it does not necessary mean the plant gets visibly damaged. For example I am sure that I had temperatures around or slightly above 30C, and no plants went belly up. Maybe the way to interpret the "Min" value is that the plant may survive that temperature even for a longer period of time with marginal / no growth?

Electrical heater may not be a bad idea. I have not calculated the cost of electricity, but say if the average temperature in January is 0C (coldest month here), then it may just be enough to raise the temperature by 4-5C on average to have quite some plants make it to the spring. I guess many people run heater all over the year set to ~24C when the room is ~20C...


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## greyuriel (Apr 22, 2017)

Flowgrow.de also gives temp tolerance and optimum temps.


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## DutchMuch (Apr 12, 2017)

Really cool


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## dwalstad (Apr 14, 2006)

All this is very interesting. I'm sure that the tolerance of plants is subject to some variation with plants probably outdoing exact guidelines. When I saw my Frogbit frozen in a layer of ice in my pond, I was sure that it was done for, but come spring it just came right back!

As October approaches, I'll start covering the four containers at night. I'm thinking of fastening pieces of bubble wrap over the tops using bungee cords. Next will be the heaters. I'm hoping to keep the plants and fish going until the end of October.


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## Z1234 (Oct 25, 2016)

dwalstad said:


> All this is very interesting. I'm sure that the tolerance of plants is subject to some variation with plants probably outdoing exact guidelines. When I saw my Frogbit frozen in a layer of ice in my pond, I was sure that it was done for, but come spring it just came right back!
> 
> As October approaches, I'll start covering the four containers at night. I'm thinking of fastening pieces of bubble wrap over the tops using bungee cords. Next will be the heaters. I'm hoping to keep the plants and fish going until the end of October.


Here are some pictures from my 80 liter outdoor tank last year when water temperature got close to 0C.



































To me the plants still look reasonably intact. The red leafs is not because of cold, thy looked like that already in the autumn or before. Maybe too much light, or a little bit of iron poisoning or whatever else caused that? The white/grey discoloration was also there on the Egeria/Elodea Densa before it got too cold.

Eventually all plants got frozen, because the whole tank became essentially an ice cube.

However, I *think *these plants could have survived sub 4C temperatures (mentioned in the book for Bacopa Caroliniana and some Val) much longer than _I thought_. I can not say this for sure. Definitely, when temperatures got to 0-10 C, I could see that the tank got a bit challenged, but the decline took much longer than I thought.

What I learned is that Pistia does not like cold (say ~10C) air temperatures. I use this plant to algae control when I start a tank, so this is something I keep in mind in the spring, when I setup the outdoor tank.


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## Michael (Jul 20, 2010)

The most amazing thing about this is that the tank did not burst all the seams!


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## dwalstad (Apr 14, 2006)

Michael said:


> The most amazing thing about this is that the tank did not burst all the seams!


My thoughts exactly!


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## Moarnica (Dec 12, 2017)

Z1234 said:


> Here are some pictures from my 80 liter outdoor tank last year when water temperature got close to 0C.
> 
> 
> 
> ...


Your tank is amazing and beautiful.  What's the pinkish, brownish round leaf plant? Could you please list the plant names. I'm trying to do something similar here in NZ. Winter temperature at night often goes below 10 C so I'd better be prepared. Thank you


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## zolteeC (Dec 26, 2017)

Moarnica said:


> Your tank is amazing and beautiful.  What's the pinkish, brownish round leaf plant? Could you please list the plant names. I'm trying to do something similar here in NZ. Winter temperature at night often goes below 10 C so I'd better be prepared. Thank you


I am who posted this originally, but I lost the password for my account.

Thats ordinary Bacopa Caroliniana. Normally the color is different, but the outdoor tank made it look like this. I have never seen such colors in any of my indoor tanks. I don't know what caused this. Maybe too much sun, or too cold, or perhaps too much Fe from soil, I really don't have a clue. Also the dwarf sag is quite brownish.

If your temperatures stay above 10C, then I think you have a good chance that your NPT will survive the winter with the right plants . Unfortunately winter is somewhat colder here, so I have to re-plant it every spring.

Perhaps choosing a larger tank makes sense, then temperature fluctuations are somewhat averaged out (night/day). (Mine was 80 liter originally, but then I changed it to 200 liter the following year. Both worked here.)


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## zolteeC (Dec 26, 2017)

I setup my outdoor NPT tank this spring. The tank gets direct sunlight and now it is approx 3 months old.

I attached a photo I took from above. I believe the plant is regular hygrophila corymbosa.

It has been very hot and sunny recently and the plant turned brownish - red.

Is this normal? Do you think this is caused by sun or some other issue (i.e Fe poisoning?)?

Should I shade this tank? Algae is at bay, no issue there.


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## mysiak (Jan 17, 2018)

As far as I know, red color in aquarium plants is brought out only under strong light and it's natural defense mechanism to protect chlorophyll/chloroplast from "unhealthy" light conditions. So IMHO it makes perfect sense that you see it in outdoor tank. Though I might remember it wrongly, maybe someone else will confirm/correct me..


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## DutchMuch (Apr 12, 2017)

I have ludwigia arcuata in my 3500g pond
I have never seen it get so red b4.


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## zolteeC (Dec 26, 2017)

DutchMuch said:


> I have ludwigia arcuata in my 3500g pond
> I have never seen it get so red b4.


There is no Ludwigia Arcuata in my outdoor tank. Can you take a photo?

In my tank, not all plant went red because of excess sun light. I'll shoot a few more photos later. Also, to me it appears that the plant color is changing even during the day somewhat. Maybe it's just me, is this really possible?

I uploaded some other pictures from last year:


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## mysiak (Jan 17, 2018)

I would say that it depends also on the species. Some plants go red, some don't. Bacopa in the picture seems to be red from strong light. In my tank it's green at the substrate level and reddish at the surface. With direct sunlight I would expect it to be totally red/brown. Pennywort stays green no matter what - and this is seen also in your photo.


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