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A Guide to Feeding Plants

Written by Angus Stewart

a green fresh aromatic herbs

Fertiliser and the nutrients they supply help plants to grow faster and healthier, and it is particularly important to have a balanced fertiliser program if you’re doing fast-growing annuals and food plants, such as herbs, fruits, vegetables and flowers. A few simple principles will help in understanding what, when and how to fertilise your plants. 

Some of the finest fertilisers can be made by recycling food scraps from the home into a worm farm or bokashi bucket, and this method also has the significant added benefits of reducing food waste and carbon emissions and saving you money on fertiliser. There are systems to suit any environment, even apartment dwellers. The bokashi bucket is a fantastic solution for those who don’t have a garden or who are low on space, while worm farms, compost and liquid manure are suitable for a range of gardens and spaces.


Let’s explore a few ways of making homemade organic fertiliser, and then look at when and how to apply these.


There are two main types of fertiliser: liquid and solid. Liquid fertilisers contain dissolved nutrients which are absorbed very quickly by the plants and thus are particularly suited to fast growing plants, such as lettuce, herbs and tomatoes. Solid fertiliser, like worm castings or a nutrient-rich compost, is a long-term fertiliser that will gradually release nutrients into the soil over the course of a few weeks and will also enrich the soil with organic humus which improves the water and nutrient-holding capacity of the soil or potting mix. Both types of fertiliser have an important role to play in plant and soil health in the sustainable garden.


Liquid Organic Fertilisers

Liquid Organic Fertilisers


Worm Juice

Worm farms are highly efficient organic fertiliser producers. Worms eat kitchen scraps and other organic waste material, such as shredded paper, and release nutrients from the complex organic molecules found therein, making them accessible to plants. The worms excrete a substance known as castings (manure), a well-balanced plant food which also contains valuable traces of humus, an important component of healthy soil. When water flows through the worm castings, the nutrients in the castings dissolve into the water, and this is how to make an organic liquid fertiliser for your plants.


Most worm farms have a tap at the bottom which can be used to release the naturally accumulating liquid in the worm farm, however it is important to remember that this liquid may be very concentrated and usually needs to be diluted before it can be applied to plants. Add water at a ratio of 10 parts water to 1 part worm juice until it becomes a light brown colour, similar to the colour of a weak cup of tea, and then it is diluted enough to apply. Another useful way to get liquid worm fertiliser is simply to pour water from a full 10 litre watering can into the top of your worm farm and then collect the resulting liquid that flows through from the bottom of the worm farm, this liquid should be dilute enough to apply straight to plants but check the colour to make sure it is light brown like weak tea. This latter method can be done once a week, if necessary.



Liquid Manure

This is an easy way to make liquid organic fertiliser if you have a chicken coop or you have access to some other source of animal manure. Wearing gloves, fill an old pillow slip or a Hessian sack with manure and put it into a bucket of water, leaving it to soak for a few days or until the water has become brown. The decomposing manure will release its nutrients into the water and you can then use this liquid to feed your plants. Colour is a good guide to appropriate concentration, and as with the worm juice above, the liquid should be the colour of weak tea. If it is darker, dilute with some more water before applying to plants.


Bokashi Bucket

The bokashi bucket is an interesting method of composting, developed in Japan and is particularly suitable for apartment dwellers as it is compact and clean. The process uses an airtight bucket with a snap-on lid which you put your kitchen scraps into and then sprinkle a bran preparation containing micro-organisms on top to begin the process of decomposition inside the bucket. The particular microbes that are added to the bucket have evolved to grow and thrive in oxygen-poor conditions, and thus the process occurs in the airtight bucket, which also conveniently makes this system clean as it keeps out pests such as mice and cockroaches. If the system is operated correctly there is no appreciable odour and the air-tight lid further mitigates any odour risk.


The bucket features a chamber at the bottom to collect the liquid from the decomposition process and a tap to remove the liquid which can then be diluted and used as liquid fertiliser. Dilute it at a ratio of 10 parts water to one part bokashi liquid. When the bucket becomes full of solid residue, this can be buried in the garden, compost heap, or worm farm, if you have one. After that the process restarts with the empty bucket.


Solid organic fertilisers


Worm castings

Liquid worm juice is great for giving your plants an instant boost, but the solids or ‘castings’ left at the end of the breakdown process are an excellent soil conditioner as well as being fantastic fertiliser. When the organic matter in your worm farm looks like the consistency of soil, then it’s ready to use. Tip the castings into a pile on a large sheet of plastic and any worms on top will burrow away from the light, allowing you to scrape off the top 2cm layer of castings. Repeat this process until all you have left in the original pile is a small pile of castings with heaps of worms in it. The ‘scrapings’ in your other pile should be worm free and can be sprinkled over your garden soil or mixed with potting mix at a ratio of about 1 part castings to 5 to 10 parts soil or potting mix.


When to fertilise

The general rule for when to fertilise is to follow the plant’s natural growing cycle – for most plants this means more fertiliser in spring and summer and about half as much in autumn and winter. However, there are some plants, like winter vegetables and spring bulbs, that continue to grow through winter and so can be fertilised more often during this time.


Liquid fertilisers can be simply diluted to the right strength (see above for how to do this) and applied to the soil or as a spray on the leaves. Solid fertiliser, such as worm castings, compost, and manure, are best applied either as a pre-planting application that is dug into the soil or, as a thin layer that is gently forked into the soil around existing plantings such as shrubs when plants are growing fastest and need more nutrients. Place a layer a few centimetres thick around the base of the plant and then place a coarse inert mulch (such as wood chip or coarse gravel) on top of that to retain moisture and keep weeds down. Solid fertilisers can also be combined with soil when making new garden beds or potting plants up to increase the quality of the soil and provide slow-release nutrients.


Making your own organic fertiliser is surprisingly easy, reduces waste, and provides a well-balanced and nutritious fertiliser and soil conditioner for the garden. Applying this to your plants according to their needs throughout the year will give you a strong, healthy and productive garden. 

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