1. RHS Level 2
Certificate
Week 5: Mulches and composting

2. Quiz on weeks 3 and 4
 7 questions – 15 minutes
 Test conditions
 Better than 3 or 4 right and you are
doing well at this stage.

3. Quiz answers
1. (c)
2. (a), (c) and (d)
3. Benefit: prevents run off; levels soil; provides
fine structure for seeds; incorporates dry
fertilizers etc
Limitation: Can lead to capping; does not
improve structure overall; risk of wind erosion
if over-raked.
4. capillary
5. (b), (c) and (d)

4. Quiz answers continued
6.Sandy
7.Anyfrom: garden compost; farm yard
manure; mushroom compost; leaf
mould.
More than 3 or 4 right and you are doing
well. Less than that and you need to
review your notes.

5. Learning objectives
 5.5 List FOUR bulky organic materials used as organic
soil mulches, including chipped bark products, leaf
mould, composted straw products, cocoa shell.
 5.6 Compare the benefits and limitations of each of the
materials listed in 5.5 for use as a mulch.
 5.7 Describe FOUR methods of composting garden
waste, including aerobic and anaerobic methods,
production of leaf mould and the use of wormeries.
 5.8 Describe the contribution made by earthworms,
bacteria and fungi to the organic matter content of the
soil.
 5.9 State the importance of the ratio of ‘green’ to
‘woody’ material in the breakdown of organic matter,
and the importance of lime to the composting process.

6. Advantages and limitations of
adding organic matter to the
soil
Advantages Limitations
Improves drainage and Needs to be regularly
water holding capacity applied in bulk –
especially intensively
cultivated soils
Encourages formation of Breaks down more
‘crumb’ structure quickly in well aerated,
well drained soils
Darkens soil so it warms Can acidify the soil as it
more quickly decomposes
Improves CEC Likely to need to import
material

7. Organic Mulches - benefits
 Applied to the soil to reduce weed
growth and retain water.
 Can prevent soil capping on silty soils
 Retains warmth in the soil, producing
a more steady temperature
 Can be used to protect more tender
herbaceous perennials from frost.
 Can be decorative and protect plants
from splashes of soil

8. Organic mulches -
limitations
 Slow to break down so do not
significantly increase soil organic
matter on their own.
 Need to be thick to suppress weeds –
10cm at least.
 Can rob the soil of nitrogen whilst
decomposing
 Must not touch the stems of woody
plants or fungal diseases will enter.

9. Types of Organic Mulch -
Bark
 Chipped bark – forestry by-product.
Comes in a number of different
grades
 Easily available and a good weed
suppressant
 However it can rob the soil of nitrogen
and can be easily blown about. Some
risk of introduction of honey fungus in
wood chip products.

10. Types of organic mulch –
Leaf mould
 Essentially free if you make your own;
recycles waste. A good soil improver
if dug in before being replaced.
 Difficult to obtain in any quantity.
 Composted pine needles produce
acidic leaf mould that is good for acid
loving plants.

11. Types of organic mulch –
composted straw
 Either produced in the garden or
purchased as mineralised composted
straw (‘Strulch’).
 If mineralised, long lasting and a good
soil improver. However, expensive to
buy.
 Home made will need storage space
(takes up to two years); can rob the
soil of nitrogen and can be messy.

12. Types of organic mulch –
cocoa shell
 By-product of the chocolate industry
so recycles waste.
 Benefits – long life; pleasant smell;
easy to handle; Contains nitrogen so
does not rob the soil; good weed
suppressant.
 Limitations – toxic to dogs when fresh;
shipped to the UK so not necessarily
‘green’. Forms a hard crust which
may reduce water penetration.

13. Composting – garden
compost
 Hot Heap method (aerobic composting)–
careful balance of carbon and nitrogen and
regular aeration.
 Benefits– kills weed seeds and (some)
fungal spores; quick method (3-6 months).
 Limitation – need to store materials (browns
and greens) to get the right mix; effort of
turning; volume needed.

14. Composting – garden
compost
 Cool Heap method (anaerobic composting)-
less care with carbon – nitrogen balance, no
turning.
 Benefits – less effort than a Hot Heap; requires
less volume of material.
 Limitations – much slower than aerobic
composting (at least a year); does not kill weed
seeds or fungal spores; can produce smelly,
slimy compost if too wet/too much nitrogen.

15. Composting – leaf mould
 Fallen autumn leaves are allowed to rot in
either a chicken wire frame or punctured
plastic bags.
 Benefits – produces an excellent soil
conditioner.
 Limitations – hard to get enough leaves to
make a significant amount; slow process (1-
2 years).

16. Composting - Wormeries
 A small scale method for composting kitchen
scraps and some card or paper using brandling
worms.
 Benefits – Wormeries can be used inside the
house in the kitchen or garage etc. Produces a
high nutrient compost and a liquid feed (must be
diluted)
 Limitations – care needed to keep the conditions
right (not too wet or too acidic); regular care and
inspection required. Small scale only for
domestic use.

17. Learning outcomes
 5.5 List FOUR bulky organic materials used as organic
soil mulches, including chipped bark products, leaf
mould, composted straw products, cocoa shell.
 5.6 Compare the benefits and limitations of each of the
materials listed in 5.5 for use as a mulch.
 5.7 Describe FOUR methods of composting garden
waste, including aerobic and anaerobic methods,
production of leaf mould and the use of wormeries.
 5.8 Describe the contribution made by earthworms,
bacteria and fungi to the organic matter content of the
soil.
 5.9 State the importance of the ratio of ‘green’ to
‘woody’ material in the breakdown of organic matter,
and the importance of lime to the composting process.