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presumably vals are root feeders, but what about giant hygro?
Is there a way to tell what plants feed thru roots and what don,t?
It is deceptive though as java ferns and anubias have roots and everyone says they don't feed thru the roots. Where do you find out which are which, please?
mouse
 

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Most plants are both root feeders and water column feeders. Some are more of one than the other. So called water column feeders will sprout roots and begin feeding thru their roots. Swords are heavy root feeders and will benefit the most from a healthy substrate. Hygros are both. Most plants wil get their nutrition from where ever they can get it.

Marcel
 

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no but there are rules of thumbs

e.g

Crypts, echinodorus sp., rhizome plants not including anubias and bulbs like to be root fed.

Generally stem plants like to be both fed, but take alot out of the water column.
 

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From Tom Barr:

Tom Barr said:
Actually most all aquatic plants will get nutrients through either the leaves or the roots(if they have them). Problem is that in nature often there are very low nutrients in the water column.

If you supply good nutrient levels to the water column, the plants will take it up from there.

This has been shown in numerous research studies on aquatic plants(Madsen and Cedergreen 2001 etc), and you can also try it yourself by using inorganic salts like KNO3.

Adding a little something under the plants will not hurt but neither will adding it to the water column.


Plants do not "Prefer" root uptake over water column uptake, it is simply a function of their variable environment which tends to have low nutrient levels in the water column overall.
 

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Just to add, many plants do have a "preffered" method of nutrient source which can effect the growth rate and overall look of the same plant.
For instance you mentioned Java Ferns... they do feed through their roots also and they will root in substrate if givin the chance but the plant seems to lose growth rate when too much of its roots are not freely available to the water column. I have found that they actually get a growth burst when the roots are trimmed occasionally. This is why you see most of the ferns strapped to wood or stone, the roots will rot if they get buried or get to thickly piled and it effects growth. :(
The same applies to say swords, only reversed, they will grow without being in a good nutrient rich substrate but they will not compare in growth to those that are buried and well fed.
Generally, you can tell just by looking at a plants root system to tell which they prefer... if they are hairlike roots , they are more for holding a plant in place rather then feeding and will enjoy a nutrient rich water column but if the roots are larger like crypts,swords, anubias etc. then its a good chance it "prefers" to fed through the substrate.
Of course thats not exact science , just an opinion.... :lol:
 

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Here's another opinion, and it kind of build's on Buck's observations while keeping in line with Tom's: I think the benefit of substrate fertilization is the ability to keep nutrients localized and at a relatively constant level through sustained time-release in the vicinity of plants that benefit from consistent levels of nutrients. These plants are those that tend to develop huge root systems and that we traditionally consider 'root-feeders' such as Amazon swords, lotus, crypts, or water hyacinth. While they're equally efficient at extracting nutrients from the water column and from the substrate, they seem to benefit tremendously from having their 'own' exclusive access to high nutrient concentrations at the roots.
 
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