Homemade Fertilisers
Students’ Sheet
Introduction
Many commercial fertilisers are available in gardening stores and garden centres for use at
home. However, there are also many websites that give advice and suggestions for making
homemade fertilisers.
Below is the introduction to an article from Gardening Know How about making fertilisers at
home.
Homemade Plant Food: Organic Plant Food
Recipes To Make At Home
“Plant fertilizer purchased from the local garden
nursery often has chemicals that not only may harm
your plants, but are not environmentally friendly.
They don’t sound particularly edible either. In
addition, they can be a bit pricey. For this reason,
many gardeners are making plant food themselves
using organic plant food recipes.”
Fertilisers are not ‘plant food’
Fertilisers are sometimes labelled
‘plant food’. This is not correct.
They contain nutrients essential for
plant growth, but they are not
energy stores and, therefore, not
‘food’.
The article goes on to describe some ‘organic plant food recipes’, including ‘Homemade plant
food’ and ‘Epsom salts plant fertiliser’.
Nutrients
Compounds essential for healthy plant growth are made from one or more atoms of certain
elements. The three elements whose compounds are need in the largest quantities are:
Nitrogen, N; Phosphorous, P; Potassium, K
The next three needed, but in small quantities are Sulfur, S; Magnesium, Mg; Calcium, Ca
Plants also need much smaller quantities of compounds of several other elements.
Activities
Activity 1: ‘Homemade plant food’
To make this fertiliser
Mix uniformly, in parts by volume:
4 parts seed meal
1/4 part ordinary agricultural lime, best finely ground
1/4 part gypsum (or double the agricultural lime)
1/2 part dolomitic lime
Questions
You will probably need to do some research to answer some of these questions.
1. Why is it incorrect to describe this fertiliser as ‘plant food’?
Science & Plants for Schools: www.saps.org.uk
Homemade Fertilisers: p. 1
2. Plants whose seeds are used to make seed meal include flax (linseed) and cotton. Find out
how flaxseed meal is made. Other seed meal is made by similar processes.
3. Find the chemical names for
(a) ‘agricultural lime’ (also called agricultural limestone), (b) ‘gypsum’, (c) ‘dolomitic lime’
4. If ‘double the agricultural lime’ is used rather than gypsum, which essential element would not
be present in the fertiliser?
5. Why is it important to ‘Mix uniformly’?
6. All of the ingredients are solids. Suggest a reason why the measurements are given in ‘parts
by volume’.
Activity 2: ‘Epsom salts plant fertiliser’
To make this fertiliser you need
1 teaspoon baking powder
1 teaspoon Epsom salts
1 teaspoon saltpetre
½ teaspoon ammonia
which you should
Combine with 1 gallon of water and store in an airtight container.
Questions
You will probably need to do some research to answer some of these questions.
1. Find out the chemical names for
(a) ‘baking powder’, (b) ‘Epsom salts’, (c) ‘saltpetre’.
2. ‘ammonia’ is solution of ammonia gas in water. It can be bought in some stores as ‘household
ammonia’. Try to find the concentration of household ammonia.
3. Find (a) the mass in g of ‘1 teaspoon’ of a solid, (b) the volume in cm3 of ‘1 teaspoon’ of liquid,
(c) the volume in cm3 of ‘1 gallon of water’.
Activity 3: Testing ‘Epsom salts plant fertiliser’
The article also says
BEFORE USING ANY HOMEMADE MIX: It should be noted that anytime you use a home mix,
you should always test it out on a small portion of the plant first to make sure that it will not harm
the plant. In addition, it is important that a home mixture never be applied to any plant on a hot or
brightly sunny day, as this will quickly lead to burning of the plant and its ultimate demise.
You will be given protocols for investigating the
effects of nutrients on the growth of seedlings
produced from germinated seeds:
Soil culture • Water culture • Floating culture
Plan an investigation to determine the
effectiveness of your homemade ‘Epsom salts
plant fertiliser’.
If there is time you may be able to carry out an
investigation.
A protocol is a plan that allows the
design of experiments by specifying
materials, equipment and methods to be
used.
It ensures that an experiment can be
replicated in other laboratories, enabling
results to be compared and their
reliability checked.
Science & Plants for Schools: www.saps.org.uk
Homemade Fertilisers: p. 2