R2102 4.3 Explain the considerations required when growing plants in water culture

Question 1

What is hydroponics?

Answer 1

Is the cultivation of plants in nutrient solution without soils or in an inert medium such as perlite, biochar, mineral wool, expanded clay pebbles or coir

Question 2

Advantages of hydroponics (4)

Answer 2

1. Water - there is a constant supply of available water to the roots
2. Nutrition - accurate control can be achieved and hence better growth and yield
3. Conservation of water - evaporation is greatly reduced. Loss of water and nutrients minimal in recirculating systems
4. Reduced cost - reduced labour, growing medium costs and quicker turn-around time between crops

Question 2

Advantages of hydroponics (4)

Answer 2

1. Water - there is a constant supply of available water to the roots
2. Nutrition - accurate control can be achieved and hence better growth and yield
3. Conservation of water - evaporation is greatly reduced. Loss of water and nutrients minimal in recirculating systems
4. Reduced cost - reduced labour, growing medium costs and quicker turn-around time between crops

Question 3

Disadvantages of hydroponics (3)

Answer 3

1. High initial costs of running
2. Elaborate automated systems
3. Different skills required for pH and nutrient control

Question 4

Nutrient Film Technique (NFT) (5)

Answer 4

1. Still popular as inexpensive setup
2. Plants grown in a constant flow of nutrient rich water. Flow is at a depth of 1-3mm over a flat surface. This creates a film of water which flows over the roots of the plants.
3. Water is pumped in at one end of a table then returned to the reservoir at the other end of the table.
4. To monitor pH - use nitric acid or phosphoric acid to lower pH. Use potassium hydroxide to raise pH.
5. Commercial systems will have automatic control systems such as conductivity and pH meters linked to dosage pumps. There may be visual or audible alarms for any failures.

Question 5

Issues with NFT (3)

Answer 5

1. Roots contantly submerged in a film of water this prevents aeration of the rootball
2. Being submerged in water can make plants prone to bacterial disease like pythium
3. Pump failure

Question 6

Aggregate culture (6)

Answer 6

1. Nutrient solution is broken up into water films by inert solid material
2. Materials used include rockwool, perlite and expanded clay aggregates
3. Rockwool is made from rock that has been crushed, melted and spun into fibres. Provides a lightweight, absorbant, inert and sterile rooting medium usually supplied in polythene wrapped slabs and cubes
4. Plants are drip feed nutrient solution from the top and the surplus runs out the bottom.
5. Used for tomatoes, cucumbers, peppers, melons etc
6. Rockwool can be used several times before its struture breaks down. It is not biodegradable so poses a disposal problem.

Question 7

Green wall (6)

Answer 7

1. Covering walls with foliage
2. Can protect walls from rain and provide some insulation. Some claim reduced noise.
3. Hydroponic systems extend the concept of green walls to provide platforms for grow bags for plants and a drip fertigation system.
4. Kits can be purchased to cover an area in the domestic garden
5. Interior green walls can be created
6. Plants selected for green walls based on situation and purpose. e,g, sunny sites or north facing walls; desire to grow salads and fruit.

Question 8

Aeroponics

Answer 8

Creating a fine mist of nutrients sprayed inside a tube or container in which the roots of the plants are suspended.

Does not work so well in practice due to salt precipitate and calcification of water blocks the misters.

Can work by using a sprayer spinning at high frequency which stops the blocking of the mister by salt precipiate and calcification of water.