Hydroponics – SS3 Horticulture and Crop Production Lesson Note (First Term)

Hydroponics is the method of growing plants in water with dissolved nutrients, without soil.

Behavioural objectives

1. Define hydroponics and explain where the word comes from.
2. Name four growing media used in hydroponics.
3. Describe the Nutrient Film Technique, Deep Water Culture and the drip system.
4. State the advantages of hydroponics.
5. State the challenges of hydroponics.

What is hydroponics?

Hydroponics is a way of growing plants using water and added nutrients instead of soil.

• Word origin: it comes from the Greek words hydro (water) and ponos (labour).
• Role of soil in normal farming: soil holds the roots and stores water and minerals. Plants do not eat soil.
• Role of water in hydroponics: the water carries dissolved fertilisers straight to the roots, so it does the work of the soil.
• Plant energy: roots do not need to spread far to find food, so the plant can put its energy into leaves and fruits.

What is a nutrient solution?

A nutrient solution is water in which the minerals a plant needs have been dissolved.

• Fertilisers: the source of the nutrients dissolved in the water.
• pH: a measure of how acidic or alkaline the solution is. It must be kept at a level the plants can use.
• EC (electrical conductivity): a measure of how strong or concentrated the nutrient solution is.

What are the main parts of a hydroponic system?

A hydroponic system is made up of parts that hold the plants and move nutrient water to the roots.

• Reservoir (tank): holds the nutrient solution.
• Pump: moves the nutrient solution to the plants in NFT and drip systems.
• Pipes, gutters or tubes: carry the solution to the roots.
• Air pump and air stone: bubble oxygen into the water, as in a fish tank.
• Growing medium: holds the roots in place.
• Timer: switches the pump on and off at set times in drip systems.

What are growing media in hydroponics?

Growing media are materials that hold the roots in place and keep the plant upright, since there is no soil.

• Coco coir: shredded coconut husks that hold water well.
• Perlite: light, white, popcorn-like granules made from heated volcanic glass.
• Clay pebbles: round balls of burnt clay that let plenty of air reach the roots.
• Rockwool: a spongy material spun from melted rock.

• Nutrients: these media supply little or no food. The nutrient solution supplies it.

What are the main types of hydroponic systems?

There are three common types of hydroponic system: Nutrient Film Technique (NFT), Deep Water Culture (DWC) and the drip system.

1. What is the Nutrient Film Technique (NFT)?

NFT is a system in which a thin film of nutrient solution flows continuously over the roots.

• Set-up: plants sit in long PVC pipes or gutters.
• Flow: a thin stream of nutrient water runs over the tips of the roots.
• Oxygen: the upper roots stay in the air, so they get oxygen and food at the same time.
• Suitable crops: leafy greens such as lettuce and kale.

2. What is Deep Water Culture (DWC)?

DWC is a system in which the roots hang in a tub of aerated nutrient solution.

• Set-up: plants sit on a floating platform, usually styrofoam, above a large tub.
• Air stone: bubbles oxygen into the water so the roots do not suffocate.
• Simplicity: it is the simplest of the three systems.
• Suitable crops: fast-growing herbs and leafy vegetables.

3. What is the drip system?

The drip system is a system in which nutrient solution drips onto the base of each plant.

• Set-up: each plant grows in its own bucket of clay pebbles or coco coir.
• Dripping: a small tube drips nutrient water onto the plant every few hours.
• Reuse: extra water drains back into the tank to be used again.
• Suitable crops: larger plants such as tomatoes and peppers.

How do the three systems compare?

How does a recirculating hydroponic system work?

A recirculating system pumps nutrient solution to the roots and returns the extra to the tank for reuse.

1. Fertilisers are dissolved in water in the tank.
2. The pump sends the solution through pipes to the plants.
3. The roots take in water, nutrients and oxygen.
4. The extra solution drains back into the tank.
5. The farmer checks the pH and EC and corrects them when needed.

What are the advantages of hydroponics?

The advantages of hydroponics are saving water, saving space, avoiding soil problems, fast growth and climate control.

1. Water saving: the water is recycled, so far less is lost than in soil farming, where water evaporates or drains away.
2. Space efficiency: plants can be grown close together or stacked in vertical farms, so more plants grow in a small area.
3. No weeds or soil pests: there are no weed seeds, and soil-borne diseases such as some fungi cannot attack the roots.
4. Faster growth: nutrients are always available at the roots, so plants often grow faster than in soil.
5. Climate control: systems are usually in greenhouses or indoors, so crops can be grown whatever the weather outside.

What is the difference between hydroponics and soil farming?

Soil farming grows crops in the ground, where the roots get water and minerals from the soil.

Hydroponics grows crops in nutrient solution, where the farmer controls what the roots receive.

What are the challenges of hydroponics?

The challenges of hydroponics are power dependency, high set-up cost and the knowledge needed to manage the system.

• Power dependency: if electricity fails and the pumps stop, roots can dry out and plants can die within hours.
• Set-up cost: pipes, pumps and sensors cost more than a hoe and seeds.
• Knowledge: the farmer must know how to mix nutrients and check pH and EC.
• Spread of disease: a disease in the shared water can reach every plant in the system.

Where can hydroponics be used?

Hydroponics can be used almost anywhere, as long as water flows, oxygen reaches the roots and nutrients stay balanced.

• Cities: it suits places where land is scarce.
• Rooftops: systems can be set up on roofs.
• Greenhouses: crops can be grown through the year.

Evaluation

1. Define hydroponics and give the meaning of the two Greek words in its name.
2. Name four growing media used in hydroponics.
3. Explain how the Nutrient Film Technique works.
4. Why is an air stone used in Deep Water Culture?
5. State three advantages and two challenges of hydroponics.

Assignment

Describe the drip system, name two crops it suits, and explain why a power failure is a serious problem for a hydroponic farmer.