Words

Glossary

Every new word from the lessons, A to Z, in plain language.

A

air gap
The space of air between the bottom of the pot and the top of the water.
In a Kratky container, the humid space between the net pot and the falling solution, where upper roots take in oxygen.
First in: Lesson 15, Project: grow lettuce in a jar
ammonia
A waste fish give off into the water. Too much of it hurts fish.
A nitrogen compound (NH3; in water much of it is ammonium, NH4+). Fish release it mostly through their gills, and rotting food and waste make more. It harms fish as it builds up, more so in warm water with a high pH.
First in: Lesson 18, The nitrogen cycle, step by step
aquaponics
Growing fish and plants together, so they share one loop of water.
A way of producing food that joins fish farming with growing plants in water. Bacteria turn fish waste into nutrients the plants take up, and the plants help clean the water that returns to the fish.
First in: Lesson 16, Fish and plants as partners

B

bacteria
Living things so tiny you need a microscope to see them.
Single-celled living things found almost everywhere on Earth. In aquaponics, nitrifying bacteria live in a thin, slimy film (a biofilm) on wet surfaces and change ammonia into nitrite, then nitrite into nitrate.
First in: Lesson 17, The bacteria you cannot see

C

chlorophyll
The green stuff in leaves that catches light.
The green pigment in leaf cells that absorbs light, mostly red and blue, to power photosynthesis.
First in: Lesson 5, Light and why it matters
concentrate
Plant food that is very strong. It gets mixed into lots of water before use.
A liquid or powder fertilizer in a strong form, diluted in water according to the label to make a nutrient solution.
First in: Lesson 9, The nutrient solution
cycling
Growing the helpful bacteria in a new fish system before it is ready for fish.
Building up nitrifying bacteria in a new aquaponic or fish system. Growers add a small, steady source of ammonia, often fish food, until the bacteria change ammonia into nitrite and nitrite into nitrate. It usually takes several weeks, and longer in cool water. Many growers do it with no fish in the tank.
First in: Lesson 19, Starting a system: why you wait before adding fish

D

deep water culture
A way to grow where roots hang in deep water, and a pump blows in bubbles.
A hydroponic system in which roots stay submerged in an aerated nutrient solution, usually with an air pump and air stone.
First in: Lesson 8, Six ways to do it
dissolve
To break into pieces too tiny to see and spread all through water, like sugar stirred into tea.
To mix evenly into a liquid at the level of single molecules or ions, so the mix looks clear and does not settle out.
First in: Lesson 2, What soil does, and what it does not do
drip system
A way to grow where a pump sends water through thin tubes, and drops fall onto each plant.
A system that delivers nutrient solution through tubing and emitters to the growing medium at each plant. Extra solution is either collected and reused or drained away.
First in: Lesson 8, Six ways to do it

E

ebb and flow
A way to grow where a pump floods a tray of plants, then the water drains back.
Also called flood and drain. A timer runs a pump that floods the growing tray, then the solution drains back to the reservoir and the roots are left in air.
First in: Lesson 8, Six ways to do it
EC
A number that tells you how strong the plant food in water is.
Electrical conductivity: how easily an electric current passes through water. More dissolved nutrient salts give a higher EC, often measured in mS/cm.
First in: Lesson 11, Nutrient strength: the soup test

G

grow bed
A box of gravel where the plants grow. Water from the fish tank flows through it.
In a media-bed aquaponics system, the grow bed holds gravel or clay pebbles. Tank water flows through it, the stones hold the roots, and bacteria on their surfaces turn fish waste into plant food.
First in: Lesson 23, Project: design a small aquaponics system on paper
growing medium
What a plant stands in instead of soil, like rockwool or clay pebbles.
A soilless material that holds the plant up and keeps a balance of water and air around the roots. Plural: growing media.
First in: Lesson 13, What plants stand in: growing media

H

hydroponics
Growing plants in water with plant food mixed in, and no soil.
A way of growing plants with their roots in a nutrient solution, with or without an inert growing medium, instead of in soil.
First in: Lesson 7, Growing without soil

I

invasive
A living thing from somewhere else that spreads in a new place and causes harm there.
A species that is not native to a place and whose arrival causes, or is likely to cause, harm to the environment, the economy, or human health. Released pets and escaped garden plants are two ways invasive species spread.
First in: Lesson 20, Choosing fish and plants that get along

K

Kratky method
A way to grow where you fill a tub once. As the water drops, the top roots get air.
A passive, non-circulating hydroponic method. The falling solution level leaves a growing air gap where upper roots take in oxygen.
First in: Lesson 8, Six ways to do it

N

net pot
A small cup full of holes that holds a plant up. Roots grow out through the holes.
A slotted or mesh container that supports a plant in a hydroponic system while letting roots reach the water.
First in: Lesson 7, Growing without soil
nitrate
What a second kind of bacteria makes from nitrite. Plants use it as food.
NO3−, made when nitrite-oxidizing bacteria change nitrite. Far less harmful to fish than ammonia or nitrite, and the main form of nitrogen that plants take up in aquaponics.
First in: Lesson 18, The nitrogen cycle, step by step
nitrite
What one kind of bacteria makes from ammonia. It can hurt fish too.
NO2−, made when ammonia-oxidizing bacteria use oxygen to change ammonia. It harms fish because it stops their blood from carrying oxygen well.
First in: Lesson 18, The nitrogen cycle, step by step
nitrogen
A nutrient that helps a plant grow big, green leaves.
A macronutrient (symbol N) used to build proteins and chlorophyll. A shortage shows first as pale older leaves.
First in: Lesson 4, Plant food: the nutrients and what each one is for
nitrogen cycle
The loop that turns fish waste into plant food, step by step.
The path nitrogen takes through a system. Fish waste and leftover food make ammonia, bacteria change it to nitrite and then nitrate, and plants take up the nitrate. In nature, the same kinds of bacteria do this work in soil and water too.
First in: Lesson 18, The nitrogen cycle, step by step
nutrient film
A way to grow where a thin stream of water runs down a sloped channel over the roots.
Nutrient film technique (NFT): a shallow, recirculating stream of nutrient solution flows down a sloped channel past the roots.
First in: Lesson 8, Six ways to do it
nutrient solution
Water with plant food mixed all through it.
Water with the mineral nutrients plants need dissolved in it, at a measured strength and pH.
First in: Lesson 9, The nutrient solution
nutrients
Tiny bits of plant food that roots take in with water.
Mineral elements, such as nitrogen, potassium, and iron, that a plant takes in through its roots and needs to grow.
First in: Lesson 1, What a plant actually needs

P

pH
A number that tells you how sour or how soapy water is.
A measure of how acidic or basic a liquid is, on a scale from 0 to 14.
First in: Lesson 10, pH: the nutrient lock
phosphorus
A nutrient that helps roots grow and flowers bloom.
A macronutrient (symbol P) used to store and move energy inside cells and to build DNA. Important for roots, flowers, and seeds.
First in: Lesson 4, Plant food: the nutrients and what each one is for
photosynthesis
How a leaf uses light, water, and air to make sugar.
The process plants use to turn carbon dioxide and water into sugar with light energy, giving off oxygen.
First in: Lesson 5, Light and why it matters
potassium
A nutrient that keeps the whole plant strong.
A macronutrient (symbol K) that helps control how water moves and how stomata open and close, and helps plants handle stress and disease.
First in: Lesson 4, Plant food: the nutrients and what each one is for

R

reservoir
The tub that holds the water and plant food.
The tank in a hydroponic system that stores the nutrient solution.
First in: Lesson 7, Growing without soil
root hairs
Tiny threads near the end of a root that soak up water and plant food.
Long, thin outgrowths of single cells on the root's outer layer, just behind the tip. They greatly increase the surface that touches soil water.
First in: Lesson 3, Roots: drinking, eating, breathing
root rot
When roots turn brown and soft and start to die, often after running short of air.
Decay of roots, often when warm water low in oxygen lets water molds such as Pythium attack them.
First in: Lesson 12, Oxygen at the roots
runoff
Rain or extra water that runs across the ground instead of soaking in. It can carry plant food into rivers.
Water from rain or watering that flows over the land surface into streams, rivers, and lakes. It can carry soil and fertilizer with it.
First in: Lesson 24, Water, land, and why growing methods matter

S

sensor
A small tool that measures something, like heat or pH, and sends the reading to a computer.
A device that detects a condition such as temperature, light, pH, or nutrient strength and turns it into a signal a screen or computer can record.
First in: Lesson 26, Jobs in growing: who works in this field
symptom
A sign you can see that something is wrong, like yellow leaves or brown tips.
A visible change in a plant, such as yellowing, browning, or drooping, that points to a problem. Different problems can cause similar symptoms.
First in: Lesson 14, When things go wrong: reading a sick plant

T

test kit
A set of small tests that tell you what is in your water, like ammonia and pH.
Aquaponic growers often test ammonia, nitrite, nitrate, pH, and temperature with drop tests, strips, or meters. The readings show whether fish, plants, and bacteria are in balance.
First in: Lesson 22, When things go wrong: fish, plants, or bacteria?
transpiration
Water leaving a plant's leaves as a gas you can't see.
The loss of water vapor from a plant, mostly through the stomata in its leaves. It helps pull water up through the xylem.
First in: Lesson 6, Water as a delivery system

V

vertical farm
A farm indoors where plants grow on shelves stacked one above another, under lights.
An indoor farm that grows crops in stacked layers under electric lights, often without soil, so it uses little floor space.
First in: Lesson 25, Farms in cities, deserts, and space

W

wick system
A way to grow where a strip of cloth soaks up water and carries it to the roots. No pump.
A passive hydroponic system in which a wick draws nutrient solution up from a reservoir into a growing medium by capillary action.
First in: Lesson 8, Six ways to do it
wilt
When leaves and stems go soft and droop because the plant can't get enough water.
Drooping caused by a loss of water pressure (turgor) inside the plant's cells, when the plant loses water faster than its roots take it up. In hydroponics it can mean the roots are damaged, for example by too little air.
First in: Lesson 14, When things go wrong: reading a sick plant

X

xylem
Tiny tubes in a plant's stem that carry water up from the roots.
Plant tissue made of hollow, tube-shaped cells that carries water and dissolved minerals from the roots to the leaves.
First in: Lesson 6, Water as a delivery system