R2102 4.1 - 4.3 Growing Media and Water Culture

Question 1

Advantages and disadvantages of hydroponics?

Answer 1

Advantages:

• Precise control of the nutrition requirements of the plants and hence better growth and yield; and of the root temperature.
• Constant supply of available water to the roots, therefore there is no chance of drying.
• Evaporation is reduced and loss of water and nutrients through drainage is minimal.
• There can be a reduction in labour and growing medium costs.
• Quicker turnaround between crops in protected environments.
• Can free up land for other uses and uses less land (especially if grown vertically).

Disadvantages:

• High initial costs to install and the controls of more sophisticated systems
• Environmental concerns as it does not break down at all easily

Question 2

How are nutrients supplied and what do you need to be careful of?

Answer 2

• The nutrient solution can be prepared on site using basic ingredients or ready-made mixes.
• Careful monitoring of the nutrient solution is vital as nutrients levels can change quickly as plants extract the nutrients for growth; the nutrient solution also does not have good buffering capability and as a result pH can change very quickly too.
• Nutrient levels are monitored using a conductivity meter (this measures salts) and by visually assessing the plants themselves.

Question 3

How/why is pH monitored?

Answer 3

• Maintenance of pH 6 to 6.5 is essential to prevent any precipitation of essential nutrients. For example, at high pH phosphorous is precipitated out but becomes more available as the pH drops.
• This is controlled by using a nutrient mix, adding nitric acid or phosphoric acid to lower the pH; and, where water is too acid, potassium hydroxide to raise the pH.

Question 4

How are pests/diseases controlled?

Answer 4

• Correct recirculation treatments need to be in place to prevent the build-up of water-borne pathogens.

Question 5

Name 2 types of hydroponic systems?

Answer 5

• NFT (nutrient film technique)
• Substrate culture (rockwool)

Question 6

How does NFT work?

Answer 6

• Method of growing in a shallow film of flowing water where the nutrient solution is constantly recirculated along plastic troughs (lined with capillary matting).
• The troughs must be on a slope with a minimum gradient of 1:100 to prevent stagnation of water.
• NFT provides a constant flowing supply of nutrient solution past the plant roots.
• The nutrient solution is pumped to feed the troughs directly or by header tank.
• The ideal flow rate is 4 litres per minute.
• The plants can be sat in troughs with holes or placed in blocks of rockwool, or something similar.

Question 7

What is substrate culture?

Answer 7

• Plants are propagated in Rockwool blocks
• Larger pores in Rockwool hold air; and smaller pores hold water
• Nutrient solution is provided via drippers to each block with a constant flow
• Excess solution leaves via drainage holes and is run to a recovery channel and run back to the supply tank. The water is recirculated after appropriate treatment (sterilization) and adjustment
• pH and nutrients are adjusted as for NFT

Question 8

Where can water culture be used?

Answer 8

• Green walls
• Vegetable production (crops of high economic value such as tomatoes, cucumbers, peppers, melons, lettuce, carnations, roses and strawberries)
• Interior landscaping – some houseplants can be successfully grown hydroponically (including those suitable for interior green walls). Usually, these use expanded clay aggregates.

Question 9

What are the considerations for using water culture?

Answer 9

• Aeration
• Nutrients, pH control, water supply & quality
• Pest & disease control
• Automation

Question 10

Name 2 types of hydroponic systems?

Answer 10

• NFT (nutrient film technique)
• Substrate culture (rockwool)

Question 11

What is substrate culture?

Answer 11

• Plants are propagated in Rockwool blocks
• Larger pores in Rockwool hold air; and smaller pores hold water
• Nutrient solution is provided via drippers to each block with a constant flow
• Excess solution leaves via drainage holes and is run to a recovery channel and run back to the supply tank. The water is recirculated after appropriate treatment (sterilization) and adjustment
• pH and nutrients are adjusted as for NFT

Question 12

Where can water culture be used?

Answer 12

• Green walls
• Vegetable production (crops of high economic value such as tomatoes, cucumbers, peppers, melons, lettuce, carnations, roses and strawberries)
• Interior landscaping – some houseplants can be successfully grown hydroponically (including those suitable for interior green walls). Usually, these use expanded clay aggregates.

Question 13

How are nutrients supplied?

Answer 13

• The nutrient solution can be prepared on site using basic ingredients or ready-made mixes.
• Essential that allowance for local quality is accounted for, particularly with regards to boron or zinc as these can become concentrated in the solution and reach toxic levels for plant growth.
• Careful monitoring of the nutrient solution is vital as nutrients levels can change quickly as plants extract the nutrients for growth.
• The nutrient solution also does not have good buffering capability and as a result pH can change very quickly too.
• Nutrient levels are monitored using a conductivity meter (this measures salts) and by visually assessing the plants themselves.