Soilless Culture, Growing Media and Nutrient Solutions
This domain tests substrate choice, preparation and nutrient solution management. You must distinguish buffering, sterilisation and recirculation risks.
Substrates and solutions
- Cocopeat: good water holding, needs washing and calcium buffering before use; watch potassium and sodium.
- Perlite: improves aeration and drainage; light and dusty.
- Rockwool: inert and uniform, but needs careful drainage and disposal.
- Nutrient solution: supply macro- and micronutrients, maintain pH 5.5–6.5 and EC according to crop and stage; tomato often near 2.0–2.5 dS/m, lettuce lower.
- Systems: drain-to-waste is simpler and safer; recirculation saves water but needs disinfection and constant EC/pH correction.
Worked example
New cocopeat reads pH 6.8 and EC 0.4. Reasoning: it is not yet buffered and may release potassium later. Action: wash with low-EC water, treat with calcium nitrate solution, then rinse and establish the feed recipe. After planting, check drainage EC daily and adjust the feed rather than guessing.
Traps that cost marks
- Planting directly into unbuffered cocopeat.
- Reusing substrate without sterilisation and introducing root disease.
- Setting pH outside 5.5–6.5 and locking out iron or manganese.
- Recirculating solution without monitoring sodium accumulation.