Lesson guide · Lesson 12 · Grades 3–8 · 6 min

Oxygen at the roots

Why roots sitting in water still need air, and how an air pump gives it to them.

Open the lessonPrintable worksheet

Students will

  • Explain that roots need oxygen, even when they sit in water.
  • Name the parts that bring air to the roots in a deep water tub.
  • Describe what roots look like when they run out of air.

New words

root rot
When roots turn brown and soft and start to die, often after running short of air.

Talk about it

Fish, roots, and people all need oxygen. Where does each one get it?

Check questions and answers

  1. Why does a deep water tub need an air pump?

    • The roots need air from the water (answer) Right. The bubbles mix air into the water for the roots.
    • To feed the plant sugar Not quite. The bubbles bring air, not food.
    • To keep the water warm Not quite. The bubbles are there to mix in air.

  2. The air pump broke a while ago. What do the roots look like now?

    • Brown and soft (answer) Right. Without air, the roots start to rot.
    • White and fluffy Not quite. White roots are healthy roots. These ran out of air.
    • Bright green Not quite. Healthy roots are white. Look for brown.

  3. Which water can hold more air?

    • Cool water (answer) Right. Cool water holds more air than warm water.
    • Warm water Not quite. Warm water holds less air, so roots run short sooner.
    • They hold the same Not quite. Temperature makes a difference. Cool water holds more.

Sources

  • U.S. Geological Survey, Water Science School. Dissolved Oxygen and Water.
  • Tucker, C. Pond Aeration. SRAC Publication No. 3700. Southern Regional Aquaculture Center, 2005.
  • University of Arkansas at Pine Bluff, Department of Aquaculture and Fisheries. Aeration.
  • Lazur, A. Basics of Pond Aeration. University of Maryland Extension.
  • Wilted plants with lots of water. Southwest Yard & Garden. New Mexico State University, College of Agricultural, Consumer and Environmental Sciences, 2006.
  • Geist, L. Too Much Moisture Can Hinder Root Development. University of Missouri Extension, 2025.
  • Brechner, M., and Both, A. J. Hydroponic Lettuce Handbook. Cornell Controlled Environment Agriculture, 2013.
  • Nelson, M., G. Langellotto, and L. Nackley. Hydro Hints: Deep Water Culture. EM 9455. Oregon State University Extension Service, 2025.
  • Somerville, C., Cohen, M., Pantanella, E., Stankus, A. and Lovatelli, A. Small-scale aquaponic food production: Integrated fish and plant farming. FAO Fisheries and Aquaculture Technical Paper No. 589. Food and Agriculture Organization of the United Nations, Rome, 2014.
  • Williams-Woodward, J. Root disease management in hydroponic systems. e-GRO Alert 7(6), 2022.
  • University of Kentucky Cooperative Extension. Lettuce Diseases in Kentucky. PPFS-VG-53.
  • Colorado State University Extension. Root Disease Problems and Management in Hydroponic Systems. PlantTalk Colorado 2043.
  • U.S. Geological Survey. Chapter A6.2, Dissolved Oxygen. Techniques and Methods 9-A6.2, 2020. Table 6.2-2, oxygen solubility in fresh water.
  • U.S. Environmental Protection Agency. 5.2 Dissolved Oxygen and Biochemical Oxygen Demand. Volunteer Stream Monitoring: A Methods Manual (archived).
  • Gillespie, D. Root Zone Management of Hydroponic Leafy Greens. Handout, Greenhouse Short Course, The Ohio State University, 2019.
  • Sutton, J. C., et al. Etiology and epidemiology of Pythium root rot in hydroponic crops. Summa Phytopathologica 32(4): 307-321, 2006.
  • Kratky, B. A. A suspended pot, non-circulating hydroponic method. Acta Horticulturae 648: 83-89, 2004.
  • Kratky, B. A. Three non-circulating hydroponic methods for growing lettuce. Acta Horticulturae 843: 65-72, 2009. Copy hosted by the University of Hawaii CTAHR.
  • Fitriyah, H., Budi, A. S., Maulana, R., and Setiawan, E. Controlling the Nutrition Water Level in the Non-Circulating Hydroponics based on the Top Projected Canopy Area. IJCCS 16(2), 2022.