What plants stand in: growing media
No soil. So what holds the plant up?
- A · net pot & seedling
- B · roots
- C · air stone
A plant needs something to stand in. What could it be?
Your shoes help you stand steady. Some soak up water like a sponge.
Others let it run right through.
Roots need shoes too. Something has to hold them steady in the pot.
It also decides how much water stays near them.
Growers fill the net pot with something that isn’t soil. It holds the plant up and gives roots a grip.
It’s called a growing mediumWhat a plant stands in instead of soil, like rockwool or clay pebbles.
See it in the glossary.
- A · rockwool
- B · clay pebbles
- C · coco coir
- D · perlite
Pour the same water into two pots. One holds on to lots of it.
The other lets it run straight through.
Rockwool and coco coir hold lots of water.
Rockwool is rock, melted and spun into threads. Coco coir comes from the hairy husk of coconuts.
- A · rockwool
- C · coco coir
Clay pebbles and gravel drain fast. Water runs off, and air fills the gaps.
Clay pebbles are balls of clay, heated until they puff up.
- B · clay pebbles
Too soggy, and roots can’t get air. Too dry, and they get thirsty.
So growers pick a medium that suits their system.
Your turn. Sort the shoes.
Does each medium hold water, or does it drain fast?
Put each growing medium in a bin.
Tap a card, then a bin. Or press 1 or 2 on a card.
- Nothing here yet
- Nothing here yet
Put each growing medium in a bin.
The answer:
Holds water
- Rockwool Its thin threads soak up water like a sponge.
- Coco coir Its fluffy fibers hold lots of water.
Drains fast
- Clay pebbles Water runs off the round pebbles. Air fills the gaps.
- Gravel Water slips past the hard little stones.
Check 1 of 3
What does a growing medium do?
Show the answer
Holds the plant up and gives roots a grip. Right. It works like shoes for the roots.
Check 2 of 3
Which medium drains the fastest?
Show the answer
Clay pebbles. Right. Water runs off them, and air fills the gaps.
Check 3 of 3
The roots stay soggy all the time. What could help?
Show the answer
A medium that drains faster. Right. When water drains away, air can reach the roots.
You just learned what plants stand in when there is no soil.
Go deeper: water, air, and poresOpenClose
A good growing medium balances water and air. The tiny spaces between its bits are called pores.
Narrow pores hold on to water. Wide pores drain quickly and fill with air, which roots need.
Rockwool is made by melting rock and spinning it into fibers, a bit like cotton candy. New rockwool can raise the pH of the water, so growers may soak it first.
Coco coir is made from the fibrous husk of coconuts. It holds a lot of water but still leaves room for air.
Clay pebbles are clay heated to very high temperatures until it expands. They hold little water, and they can be washed and used again.
Perlite is volcanic glass heated until it puffs up. It is so light that it can float. Guides agree it lets in plenty of air. They disagree on how much water it holds, so it is left out of the sort.
Most hydroponic media add little or no plant food. The food comes from the nutrient solution, so the grower controls it.
Sources
- Byrd, C., A. Sharma, and Q. Ying. Selecting Growing Media for Soilless Systems. CCD-TA-02. Center for Crop Diversification, University of Kentucky, 2025. Link
- Pinkerton, M. G., B. Whitman, H. Eason, and C. Gómez. Common Media Used in Hydroponics. ENH1359/EP623. UF/IFAS Extension, University of Florida. Link
- Hoidal, N., Reardon, A., Worth, L., and Rogers, M. Small-scale hydroponics. University of Minnesota Extension. Link
- Nemali, K. Looking through the pores of a soilless substrate. Controlled Environment Agriculture (Nemali Lab), Department of Horticulture and Landscape Architecture, Purdue University, 2017. Link
- Kratky, B. A. A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce. Vegetable Crops VC-1. College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa, 2010. Link