Backyard Aquaponics
A place to discuss aquaponics

So I was thinking about how trout like pretty lower water temps, and I remember reading somewhere that favourable water temps for hydroponics is 25%. So I was wondering if keeping your water cool for trout has any limiting affects on plant growth.

Say for example, in the UK, during the summer you might be striving to keep water temps low for trout, would this make it difficult to grow melons, or other plants that require hot weather? Are tropical plants compatible with the colder water temps that trout require?

If anyone has any experience with trout and melons, or any other hot weather plant with cold water fish, it would be interesting to hear about it!

You might struggle to grow many tropical plants in the UK, but things like melons, tomatoes, cucumbers, chard, cauliflower, broccoli, spinach, peas, kale, capsicums etc grow perfectly well in systems with trout.

Its not so much the temp of the water, but lukewarm is ideal for growing.

What you want the most is a slow steady complete balanced nutrient supplied to the root system. Up's and Down's in the nutrient supply is what plants don't like.

Most plants will do well enough as long as the water temperature is over 60 F (15 to 16 C). I have trout temps here except for a few brief periods in the Summer where the water gets over 75 F (roughly 24 to 25 C). Low temps do delay plant growth in the spring and also encourage some diseases. I've found in my system it's better to start plants outside the system when the system water temperature is down below 60F (15 C)(but I prefer to start from plugs even at warmer temps because it's easier to space plants). Others have found slow starts and problems getting seedlings to grow with cooler water temps as well.

really interesting responses, cheers guys. I guess from the point of view of an exterior FT trout system in UK or similar climate, this means starting plants separately and and taking measures to lift water temps to 60 f / 15 C in early spring to achieve early planting and maximum growing season, and maybe to keep autumn water temps up too.

How about perennials left in system over winter? Does anyone have rhubarb, or grapevines or even passion fruit or other perennials in AP where water temps drop to near freezing? I know these plants survive winters in UK and can be grown very satisfactorily, in soil. Would it be any different for AP?

I suspect my climate here is pretty similar to yours and what I have found is that raised wicking beds get going sooner than my AP but the AP seems to do better going into fall so the two complement each other.

As long as you aren't letting the water freeze completely I suspect most perennials will overwinter just fine. I have some asparagus that has been in the system for 3 years and started showing some spears about a week ago (big plant but unfortunately the spears are too spindly - I think I needed to plant it deeper (the crown is right at the surface) but could be lots of things and it's a seedling so who knows). Lemon grass grows like a weed and comes back every year as well - It's in a 6 x 8 ft greenhouse that's only heated to 41 F during the worst week or two of winter. The water is connected to outside and gets down to 33 F and actually completely froze the top inch of water in the fish tank this year (The outdoor grow beds where the Asparagus is had snow and ice on them during the same period). I usually divide the lemon grass and just put 3 one or two lead starts back into an 18 gallon grow bed and it fills up the grow bed twice during the year. It doesn't get going until June but I harvest at the end of August and usually by the time fall is over there's plenty more). I don't think you'd have any problems with Rhubarb or grapes although I'd probably grow Rhubarb in soil because it takes up so much space. I'm not sure about the passion fruit .

My AP rhubarb gets frosts on it in winter without any problems. FT water temp doesn't get below 5C, although it would get below that in the GBs on frosty mornings.

That's great to hear about perennials overwintering happily!

Scotty; Would you say 15 degrees is a minimum temp accross the board, or would you say it varies between plants? In the UK we "grow" some veggies like leeks over winter (growth rate is obviously minimal due to very short daylight hours), so perhaps leeks could be left in GB in lower water temps?..

About passion fruit; we are able to grow a few ornamental varieties successfully, but "passiflora edulis" (the tasty one) is a different matter by the looks of it! The purple variety may work with a heated greenhouse, but by all means would be a challenging project, tempting though if you're a big fan like me!