Turgidity of leafy greens

[Jonathan Kadish NYC AA Chair]

I visited an aquaponics farm Friday and one of the things that i was told was that it "seems like the plants aren't as rigid" when they are grown in water as you will find in the same plant grown in dirt. All of the greens they had growing were like this. Do others have the same experience or is there some imbalance in the system?

They did have a very high fish to plant ratio (several hundred large talapia 1.5-2lbs) to several hundred plants with lots of fish waste in the NFT.

 

 

[BenHehle Beamz]

it always depends on the surrounding, i guess you cant say in general plants in soil look more rigid then plants grown in hydrocultures, if you place your AP system right, and you have optimal temperature of water, then plants are same rigid as in soil. So, how was surrounding temperature, humidity and light (day time) when you visited the farm? Why plants might not look rigid, has something to do with stomata opening and osmotic pressure in protoplasts and transpiration. As the photosynthesis rate increase, the demand of CO2 of the plant also increase, so the plants needs to open the stomata to take up CO2, but at the same time it loses water from transpiration. So thats why plants look so rigid in the morning (no need to open up stomata during night) and by day time and increasing temperature and light, plants get less rigid :D

[TCLynx]

Where was this farm?  Were they in a place that this is the right time of year to be growing lettuce?  When you try to grow lettuce in a greenhouse here in Florida during much of the year, by afternoon the lettuce is struggling just because it's too hot.

[Sylvia Bernstein]

A way to get around this that I've found is if your greens are "floppy" when you harvest just put them in a produce bag in the fridge for an hour or so.  They will crisp right up.

[Harold Sukhbir]

Hi Jonathan,

This has been my observation also. The greens in the media beds have a slower growth rate as compared to the raft and are more rigid. If the gravel beds are densely planted and the media is shaded the greens won't readily wilt in the direct sunlight while the raft greens become 'floppy' under the same conditions. Increasing flow rates/DO levels and shading has greatly improved the rigidity of the greens in raft. I feel that it may have something to do with the availability of more nutrient to plants in media than in water alone but this is just an assumption. BTW very interesting tip on the freezer Sylvia, will try this next!

[Carey Ma]

I believe everyone here is on the right track. I'd suggest putting a block of ice in the grow bed stream to cool the roots and lower the nutrient concentration.

[TCLynx]

Fridge not freezer.  If you put them in the freezer they will not be nice.

 

You can also harvest and dunk in almost icy cold water or soak in cold water before washing and spinning.

 

In Raft, if the aeration isn't good you can get wilting due to lack of dissolved oxygen in the water.  If the aeration is good the plants may grow so fast that they have more trouble finding the nutrients they need if pH or other conditions are marginal.  My high pH system the plants in media less culture definitely suffer more for the iron lock out than the ones with access to media of some sort.

 

The biggest thing about limp lettuce and other greens really seems to be largely related to temperatures though.  The really crisp iceberg lettuce just doesn't normally grow well down here in FL, just not enough of a cool season for it.

[Gina Cavaliero]

Early morning harvesting and an ice bath insures a crisp product.  Typically with heating of the day, the plants will loose their rigidity but as the temps cool, they recover nicely in the evening.  Humidity has a direct effect on this too. Even a wilted green can be harvested, crisped in ice water and refrigerated and will firm back up, but its shelf life is compromised.

 

[Jonathan Kadish NYC AA Chair]

I love that I can get so many different perspectives, from gardener to scientist. Great info to consider from everyone. It was the middle of the day and about 85 and sunny in the green house so it all makes sense, so much to learn!

[Jane]

so if you have a good balance of CO2 or added CO2 would the plants be more "rigid"

BenHehle Beamz said:

it always depends on the surrounding, i guess you cant say in general plants in soil look more rigid then plants grown in hydrocultures, if you place your AP system right, and you have optimal temperature of water, then plants are same rigid as in soil. So, how was surrounding temperature, humidity and light (day time) when you visited the farm? Why plants might not look rigid, has something to do with stomata opening and osmotic pressure in protoplasts and transpiration. As the photosynthesis rate increase, the demand of CO2 of the plant also increase, so the plants needs to open the stomata to take up CO2, but at the same time it loses water from transpiration. So thats why plants look so rigid in the morning (no need to open up stomata during night) and by day time and increasing temperature and light, plants get less rigid