Water temperature and plant growth

[jessieb]

Hi everyone,

I have been battling very poor plant growth over the summer months to date with all plants except the trusty spinach failing to yield much edible produce. I have spinach, lettuce, spring onions, tomatoes, chillies, capsicums and strawberries growing at present and I gave up on all varieties of squash and cucumbers as they repeatedly died after a week in the grow beds. I have concluded that water temperature is the problem with my system frequently reaching and holding 29 degrees, with the odd drop back down to 18-19 when there is a cool change. The cool changes seem to bring about a brief improvement in plant health - evident only in the color of the leaves becoming greener.

My 248 Silver Perch are doing well with no losses in recent months and only a 3.2% loss overall since I got them in April 09. Water conditions are as follows;

PH 6.4 on average (varies between 6.4 and 6.6) buffered by crushed sea shell
Ammonia 0.25 (consistent)
Nitrates varying between 0 and 5 (more so hard to distinguish from 0)

The Digger guide to earth based gardening suggest that a very warm soil is 18 degrees and therefore I am left wondering whether the plant roots are not coping well.

I augment the nutrients every six months with mineral fertilizer purchased from Murray and there is no evidence of any iron deficiencies. Interestingly my winter growth was very agressive with water temperatures maintained at 18-22 degrees through heating (won't be heating this years as it was too expensive).

If it is water temperature, given my location of Deniliquin in NSW I would expect that Victorian and South Australia aquaponicists (is there a word for the aquaponics enthusiast) would be experience similar poor growth rates?

Any thoughts and opinions are most welcome and appreciated.

[Castaway]

Do you have any shade cloth over your system? Some photos would be helpful for others to see the problem.

[Ben]

I've had similar experiences, I only started the system in April 09 so one winter and half a summer, so no longer to compare growth rates.

My lettuce and tomatoes went nuts all through winter, since November when the ambient temp went above 34 the growth dropped. Fish have been very happy with water at 30c, plants have been average except for capsicum. Even the chili stopped fruiting, and the cabbages look sick!
I was getting burnt plants so tried shade cloth, 70% is too much, 50% is a good compromise but water temp still high 20's.
I have a few stunted sick looking plants that are staying until the seedlings get to a better size to plant out.
ATM I have taken the shade cloth off due to the overcast weather.

Will be interesting to see how the systems fair in the cooler weather! I may be growing fish in the summer and veggies in the winter!

[Murray]

Root zone temp is a very big factor for almost all plants. Lettuce, for example will not do well if root zone temp gets above 22 deg.
I am currently looking around for a second hand tucker box freezer to make up a water chiller. At the moment I am not having any luck at all getting seedlings to come up, and we are running short of lettuce due to hot root zone probs.
In late Nov early Dec we had 21 days in a row where the daytime temps were above 35 deg and the hottest day was 44 deg. Those temps knocked the plants around sometning fierce.
Pawpaw trees loved it !!!

[jessieb]

Hi guys,

I echo Ben's setup/scenario Castaway. First full summer and I had to incorporate 50% shade cloth earlier this summer as the heat coming through my clear Larerlite was too intense and was stressing out the plants to the max by the end of those 40+ days with my system placed to maximise winter sun exposure. I too have a removable system where I can roll back the shade cloth when ambient temps are more reasonable.

It is always good to hear that you have similar hurdles Murray - if nothing else I am amongst good company. I'd be curious to see how your chest freezer goes - if I recall correctly, an idea floated and perhaps tried previously but the outcome never published?

Thank goodness the spinach is hanging in there (albeit not as well as during Winter) - bring on Autumn!!

Thanks for all of your relies 8-)

[Castaway]

At the moment I am not having any luck at all getting seedlings to come up, and we are running short of lettuce due to hot root zone probs.

Aha! That explains why my lettuce seeds didn't germinate at all. I thought it was just old seeds! The Bok Choi on the other hand all shot up with no problems in the same tray. I'm using the same seed sprouting system as you Murray.

[Murray]

The water gets too hot in the tray and cooks the seeds.
I have bid on a freezer on eBay....hope I win.

[johnG]

It has been very hot even up here at Mt Tamborine. My lettuce are not doing so well but still good enough to eat.

[fishfood]

The water gets too hot in the tray and cooks the seeds.
I have bid on a freezer on eBay....hope I win.

Did you win !

[Murray]

Hi FF, Yes I did get it but the freezer will not freeze, another pile of junk from eBay and a waste of 102.50
Lee has got one in his sights, I am hopeful he will be able to get it this week.
We actually plummed the eBay freezer into the floating raft system and mucked around for a few hours getting the water flow just right, made up a poly coil with fittings to act as the heat exchanger inside the body of the freezer, so we will be able to hook up the next freezer quickly when we can score one for the trials.