R2102 4.1 – 4.3 Growing Media Flashcards
Explain considerations when growing plants in containers.
- Restricted root volume
- Water retention and supply
- Drainage
- Nutrients
- Stability of compost – crumb structure needs to withstand constant wetting
- Sterile
What are the benefits of loamless compost?
- Soilless
- Lighter
- Cleaner to handle
- Cheaper – doesn’t need sterilising
- Until recently used peat now use alternatives
Peat alternatives?
- Coir (coconut fibre)
- Garden compost
- Wood based – bark sawdust paper etc
- Locally available materials such as straw wool etc
State 2 limitations of using a garden soil as a growing medium in containers.
- Garden soil has an unknown concentration of nutrients
- Soil structure may be poor/lacking in organic matter/pore space
- Soil texture may be poor, i.e. too much clay/small particles
- Pests and diseases/weed seeds may be present which affect plant growth
State the effects of growing acid-loving plants in alkaline soils.
- stunted growth
- lime-induced chlorosis
- nutrient availability decreases, e.g. phosphorus, iron, manganese and boron which may result in deficiencies
How are nutrients supplied?
- 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.
How/why is pH monitored?
- 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.
How are pests/diseases controlled?
• Correct recirculation treatments need to be in place to prevent the build-up of water-borne pathogens.
What are the considerations for using water culture?
- Aeration
- Nutrients, pH control, water supply & quality
- Pest & disease control
- Automation
Name a situation for each different type of compost.
Multi-purpose composts – raising seed, potting on, hanging baskets (specifically designed)
Ericaceous – calcifuges (loam- or peat-based and does not have added lime)
Seed composts – do not require nutrients. Large quantities of nutrients would be harmful and could even prevent germination and potential scorching of seedlings. Good aeration and good moisture retention is needed for seed composts.
Cuttings composts – require a high air-filled porosity. The main reason for cuttings failing is from fungal diseases and the cutting rotting. Adequate air in the growing medium will help prevent this. A good mix for cutting composts is 50% of a material such as composted bark and 50% of an opening material to provide good drainage such as perlite, coarse sand or grit.
Advantages and disadvantages of using peat?
Advantages –
- Light, cleaner to handle and easier to store.
- Already partially sterile and provides a uniform product.
- Good for hanging baskets as lightweight.
Disadvantages –
- As the compost is light the staking of tall, heavy plants can be problematic.
- It is often very difficult to rehydrate when dry.
- There is also the greater chance of toxicity due to reduced buffering capacity (i.e. the ability to resist changes in pH).
What is loam-based compost?
- Good physical structure, adequate and balanced supply of nutrients, free from harmful organisms.
- Materials used are loam, peat, sand and a balanced proportion of fertilisers.
- Partially sterile.
- Moss peats and sedge peats are used to aid moisture retention. Normally sterile and free from weeds, pests and diseases. Avoid very dusty forms. The best types are fibrous or granulated.
- Sand is important for adequate drainage and good structure. This should be clean and sharp, free from clay, silt, organic matter and lime. River-bed sand is suitable.
+ and – of loam-based compost?
Advantages:
- Useful for plants that are to be in containers long term, such as shrubs, as it is very stable.
- They have a high level of buffering which means they are stable and avoid fluctuating water and nutrient content.
- Clay content of loam provides a longer supply of nutrients.
- The weight of the loam provides stability for the container. Therefore good for outdoors as less likely to be blown over.
- Also good for plants that will eventually be planted in open ground as the root systems are better adapted to soil conditions.
Disadvantages:
- The weight does make the it difficult to move containers and not suitable for hanging baskets.
- The ‘fines’ can fill or block the air spaces within the growing media which are really important for drainage and aeration in the root zone.
Peat alternatives?
- Coir (starting seeds, with 50% compost? micro greens, mixed with potting mix); pest resistant, see https://www.youtube.com/watch?v=czWLku1giMI, on wormery post use. But no nutrients…
- Composted green waste (soil amendment, reducing fertiliser use and improving soil health), boost soil structure and help with water retention
- Composted bark (a rich source of organic nutrients slowly released into soil, improving fertility and adding humus to soil. Mulching around trees and shrubs as well as beds, borders and vegetable plots.)
State a limitation of using garden soil in containers.
- Soil may contain pests and weed seeds
- The nutrient content of the soil is not known
- Soil type may not be suitable for the type of plant being grown
- Soil may be too heavy if the containers need to be moved
