RHS Level 2 Certificate

Year 2 Week 8 – fertilizers and alternative growing media.

Learning objectives - fertilizers 7.6 State what is meant by the terms ‘organic fertiliser’

and ‘inorganic fertiliser’ and list TWO examples of EACH.

7.7 State TWO benefits and TWO limitations of using organic fertilisers and inorganic fertilisers.

7.8 State what is meant by: single or straight fertilisers; compound fertilisers. List TWO examples of EACH

7.9 State what is meant by the terms ‘Base dressing’, ‘Top dressing’, ‘Liquid feed’ and

‘Foliar feed’. Describe ONE situation where EACH type of fertiliser application would be appropriate.

7.10 Describe the use of Controlled Release Fertiliser (CRF) granules and state TWO benefits and TWO limitations of their use in growing media.

Learning objectives – alternative growing media

8. Understand the uses of alternative growing media

8.1 Describe the range of compost types available, and the use of EACH of these growing media as alternatives to growing in soil: including peat-based, loam-based, peat-free, multipurpose, ericaceous, seed and cutting and container composts.

8.2 State how air-fill porosity, water holding capacity, and stability of growing media affect plant growth

8.3 Describe the environmental implications of the use of peat, coir and municipal green waste in growing media.

Fertilizers – soil testing

Three approaches• Rule of thumb – suitable for non-cropping

situations.• Follow fertilizer intervals recommended –

e.g. N each year perhaps several times, P annually and K every second or third year.

• Soil testing – macro only (DIY) or full nutrient analysis via laboratory. Required to diagnose excess/deficiency accurately.

Fertilizers – organic and inorganic Organic fertilizers are made from once living

materials (Fish, Blood and Bone etc). Inorganic fertilizers are derived from non-

living sources such as rocks (Phosphate) or by synthesis from fossil fuels (e.g. Nitrogen via the Haber process).

Do not confuse with ‘organic’ growing practices

Fertilizers may be ‘straight’ (single nutrient) or ‘compound’ (more than one nutrient).

Organic fertilizers – sources and characteristicsFertilizer Characteristics

Bone meal – heat treated crushed animal bone. A compound fertilizer

Some Nitrogen, mostly phosphorous, no potassium. 4:15:0 (4% N: 15%P;0% K)

Fish, blood and bone (compound)

Contains all three macro-nutrients (with the potassium coming from rock potash) 5:5:6

Wood ash Potassium – the only organic source of potassium at about 6% by dry weight

Organic fertilizers – advantages and disadvantages

Advantages Disadvantages

Slow release – so less risk of leaching

Requires microbial activity

Recycles food production waste

Low concentrations of nutrients per volume

Encourages beneficial soil organisms

May attract vermin.

Lower soil salinity after use

Powder (meal) less easy to spread evenly

Inorganic fertilizers – sources and characteristics

Sodium Nitrate (Straight)

About 16% N by dry weight (as nitrate)

Triple Super Phosphate (Straight)

43% Phosphorous

Potassium Chloride (Straight)

60% Potassium

Growmore (compound)

7: 7: 7 (7% N: 7% P and 7% K)

Inorganic fertilizers – advantages and disadvantages

Easy to get exactly what is required

High consumption of fossil fuels – releasing CO2.

Water soluble –so soil temperature not crucial

Will leach readily if applied at the wrong time or in excess.

Very concentrated so less needed

Increases soil salinity with regular use.

Cheap ‘Straights’ are easy to over apply

Application methods Base Dressing – applied before planting Top Dressing – applied to existing planting. Foliar Feed – solution sprayed onto and

taken up by the leaves. Liquid feed – solution applied diluted to the

growing media or soil. Controlled Release Granules or tablets –

compound fertilizer in polymer shell. Release over time triggered by soil temperature.

CRF – advantages and limitations

Release linked to soil temperature and growth rates.

Expensive

Reduced leaching Polymer remains in soil and decomposes slowly

Single application – less work

Single application – hard to adjust later

Avoids high salinity in containers – unlike liquid feed

Not ideal for open ground – due to above.

Alternative Growing Media – basic concepts

Air Filled Porosity – the percentage of pores in the growing media that will hold air once gravitational water has drained.

Water Holding Capacity – used to describe the water content after drainage.

Bulk Density – weight per unit volume Stability – ability of the media to form and

retain a good structure over time.

Nutrient Content and pH

The nutrient content of growing media varies according to their use. For example cuttings compost contains no added nutrients and seed compost very little (perhaps a little added phosphate). Multi-purpose compost contains N, P and K.

pH varies though most are approximately neutral. Calcifuges will need ericaceous compost which is acidic.

Materials used – Peat based

Has good AFP and low Bulk Density, making it cheap to transport. Good WHC but hard to re-wet once dried out. Usually contains re-wetting agent because of this.

Peat contains no nutrients of its own so it is easy to add what is required.

Environmentally problematic due to destruction of wetlands and CO2 emissions from processed peat and drained bogs.

Materials – peat alternatives

Coir – made from coconut husks; good AFP and WHC. Re-wets easily, unlike peat. Low Bulk Density. Has been criticised for relatively rapid decomposition though this may be down to quality. Low in nutrients in original state

Wood waste – composted bark or sawdust. Good AFP and WHC. Higher Bulk Density than peat or coir. Low in nutrients.

Composted Green Waste – variable AFP and WHC (though British Standard now introduced). High in nutrients so not suitable for seed or cuttings mixes.

Loam based growing media

John Innes is the name of a standard formulation – not a brand name.

There are JI seed, cuttings, potting and general use composts.

Based on sieved loam, peat and sand with added lime and variable amounts of JI Base Fertilizer depending on use.

High Bulk Density makes them suitable for long term planting (but harder to handle and more expensive to transport); medium AFP and good WHC (dry out less easily than organic media).

Ericaceous version available.

Learning Outcomes - Fertilizers 7.6 State what is meant by the terms ‘organic fertiliser’

and ‘inorganic fertiliser’ and list TWO examples of EACH.

7.7 State TWO benefits and TWO limitations of using organic fertilisers and inorganic fertilisers.

7.8 State what is meant by: single or straight fertilisers; compound fertilisers. List TWO examples of EACH

7.9 State what is meant by the terms ‘Base dressing’, ‘Top dressing’, ‘Liquid feed’ and

‘Foliar feed’. Describe ONE situation where EACH type of fertiliser application would be appropriate.

7.10 Describe the use of Controlled Release Fertiliser (CRF) granules and state TWO benefits and TWO limitations of their use in growing media.

Learning Outcomes – Alternative Growing Media

8. Understand the uses of alternative growing media

8.1 Describe the range of compost types available, and the use of EACH of these growing media as alternatives to growing in soil: including peat-based, loam-based, peat-free, multipurpose, ericaceous, seed and cutting and container composts.

8.2 State how air-fill porosity, water holding capacity, and stability of growing media affect plant growth

8.3 Describe the environmental implications of the use of peat, coir and municipal green waste in growing media.