Expert: Dana Krempels, Ph.D. - 7/3/2007

Question
how can a floating pond plant,such as duckweed,survive without having its roots in soil?

Answer
Dear Bautista,

I just found your question in the Biology question pool, and thought I could help.

Plant roots don't need to be in soil as long as there are sufficient dissolved nutrients in whatever substrate the roots contact.  This is why hydroponics works:  you just add the necessary nutrients (nitrogen, phosphorus, potassium, trace minerals) to the water the plant roots are sitting in, and voila!  The roots can absorb them just as easily directly from the water as they can from the soil.

In soil, plant roots actually grow between the soil particles, contacting water in between the particles directly.  They never actually grow into the soil particles themselves.  Roots can obtain nutrients ONLY if they are wet (only dissolved nutrients can pass into the roots), so absorbing them directly from water is actually less of a problem than getting them from dry soil.

Hope that helps!

Dana