MadSci Network: Agricultural Sciences

Re: How does hydroponics work?

Date: Tue May 12 18:12:18 1998
Posted By: Eric Biddinger, Grad Student, Horticulture, Penn State University
Area of science: Agricultural Sciences
ID: 894579113.Ag

MadSci Network: Agricultural Sciences


Thanks for the question. This just happens to be one of my favorite subjects!!!

The term "hydroponics", as used today, includes quite a range of growing systems. Hydroponics can best be defined as, "growing plants without the use of soil." There are many variations on hydroponic systems. Some replace the soil with an inert medium such as sand, gravel, perlite, rockwool, or sawdust (also called soilless culture). Other systems suspend the roots of the plant directly in the nutrient solution (Water culture) or hold the roots in the air, misting frequently with the nutrient solution (Air culture or Aeroponics).

Hydroponic systems vary greatly. The design and function depend on what plant is being grown, what the purpose of the system is, what resources are available (greenhouse, lighting, water supply, etc.).

The best way to understand hydroponics is to think about what the soil provides the plants: Water, aeration around the roots, nutrients, and physical support. All we need to do to grow plants hydroponically is to find another way to meet these requirements for the plant!

Supplying the water is done by either flooding the roots or using a media to hold the water. Nutrients are dissolved in the water. The support can be provided by the growing medium or by some part of the growing system. Finally, aeration can be achieved by bubbling air through the water, recirculating the water, or using a porous media which will hold air.

Advantages of hydroponic systems (paraphrased from Hydroponic Food Production by Howard Resh (1995)). 1) Nutrients can be completely controlled providing the plant with the right amount of nutrients for the stage of growth it is in.
2) The growing media and environment can be kept clean of disease problems.
3) No soil born insects and diseases to infect the plants.
4) Spacing is only limited by light, not water and nutrients, allowing for increased yields per unit area.
5) No weeds - enough said!
6) No water stress during plant growth increasing health and yield.
7) Better product quality (no sand in the lettuce, no discoloration of the cucumbers from laying on the ground, etc.).
8) More efficient use of fertilizers.
9)Reduced use of pesticides on the crops.
10) Higher yields!

But hydroponic systems do have their share of problems:
1) Very expensive to build and operate even a small production operation.
2) Hydroponics requires a good knowledge of plant pathology, plant nutrition, and basic chemistry.
3) A small insect problem can cause much more damage than it would in the field.
4) Bacterial diseases can spread quickly in a hydroponic system.
5) Maintenance of the plants is VERY labor intensive.
6) Constant supervision required to watch for problems.
7) Mechanical breakdowns and electrical failures can cause serious crop loss.

The use of hydroponics has dramatically increased in the last decade and will probably continue to rise. Hydroponics are used in research primarily for nutrient studies. Growers are increasingly taking advantage of the higher quality produce in order to deliver a high value crop to specialty markets and consumers. And yes, NASA has been experimenting with using hydroponics in space for quite some time.

Plants in space offer some really challenging problems. Try looking up Controlled Ecological Life Support Systems (CELSS, pronounced "cells") to find more information about plants in space. Here is a good starting point from Utah State University.

Concerning further information about hydroponics, there are a lot of good basic books out there which can be found in many libraies. Many Web pages cover the topic as well.
Thanks for the question!

Eric J. Biddinger
Grad Student - Department of Horticulture
Penn State University

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