Composting: Kitchen waste, NPK & Fertilisers

Home Style Composting

Composting is a very important section of any good gardening book – but they all fail to mention how wonderful good ol’ kitchen waste is. Some say it takes too long to break down and that it must be degraded before planting... but that is a bunch of half-truths. Kitchen waste will break down while your plants grow and the plant roots will assist with decomposition. So when you plant new seeds or seedlings - add a little kitchen waste to the planting hole, as you would fertiliser. It also is easier to add kitchen waste directly to the garden, since many gardeners do not have enough space for a compost heap or bin. Composting kitchen waste is very sustainable, since it is readily available, high in nutrients, reduces the waste on landfills and is a way of accessing a free service provided by mother nature to assist with your vegetable gardening efforts.

The lowdown: Kitchen waste has an astounding amount of nutrients and breaks down within 1-2 months depending on the season and what you put in the ground. Most things (tea bags, leaf based stuff, whole fruits and vegetables, banana peels) breaks down in 1-2 months, stuff like avocado peels take longer J.

B&B - Banana and Beet Lore
Banana peels and beet leaves are some of the the best nutrients from the kitchen (next to comfrey, but that’s not kitchen waste J) you can give the soil and the plants – I always aim for high potassium foods – not just for fruit and flowers, but for plant resistance! Earthworms love them too!

I did a nutrient study to determine, which is the best kitchen waste to add to my home-style composting, focusing on most of the main plant nutrients – NPK, Mg, Ca, Na:

Food (100g)	Nutrient	Amount of nutrient (mg)
Comfrey (herb)	N, P, K	1190, 100, 740
Banana	Mg, P, K	27, 22, 358
Beet Greens	Ca, Mg, P, K, Na, Fe	117, 70, 41, 762, 226, 2.6
Carrot Greens	Ca, P, K, Na	33, 35, 320, 69
Borage (herb)	Ca, Mg, P, K, Na	93, 52, 53, 470, 80
Turnip greens	Ca, Mg, P, K, Na	190, 31, 42, 296, 40
Orange Peel	Ca, Mg, P, K	161, 22, 21, 212
Beans	Ca, Mg, P, K, Na, Fe, Zn	37, 33, 129, 332, 25, 1, 1
Peas	Ca, Mg, P, K, Na, Fe,  Zn	25, 33, 108, 244, 5, 1.5, 1.2
Squash	Ca, Mg, P, K, Na	15, 17, 38, 262, 2
Basil (herb)	Ca, Mg, P, K, Fe	177, 64, 56, 295, 3.2

Now I only added the elements in the nutrient table that matter (values of one type of food relative to the trend amongst all the food), do not want to bore you with numbers. So regarding the table, comfrey is best, followed by borage, but these are herbs and need to be grown specifically for composting. So for kitchen waste: Beets, Bananas, Carrot, Basil … I think you get the picture J. So no throwing away carrot or beet greens! The earthworms will get you!!

Earthworms & Wormeries

Kitchen waste:
Just about anything that is plant based, leaves, roots, shoots, flowers, fruits … seeds! Anything rotten or that you won’t eat (carrot greens) go back into the ground – if it is safe to lick, it goes in!

Just have a large plastic container with a lid in your kitchen that can take about three days worth of kitchen plant material – more than three days sitting it goes really gloopy. Once full, dig a hole in the garden and plop it in there - you can plant immediately once covered. Or put in a ‘drier’. I dry any excess kitchen waste for, which there is no space in the garden – a very large plastic drum (laundry holding size) and put it in the sun – mine takes 1-2 days to dry out to a crisp! Breaks down in a snap when it is dry and then added to the soil.

Kitchen waste you can give to garden in copious amounts:

Banana peels	Carrot leaves	Beet greens	Herb leaves (everything, lavender, basil, sage…)	Herb stems	Vegetable shavings (after peeling)
Tea bags!	Spent coffee	Onion leaves	Roots (from spinach or lettuce harvesting)	Citrus peels	Rotten stuff: tomatoes, peppers, apples…
Spent spices	Flowers (rose petals, squash flowers)	Turnip and radish greens	Peels (pineapple, squash, carrots, potato)

Basically anything that is plant-based can go into the ground – do not bother with processed foods like bread, cheese – as these have little nutrient value for plants in terms of NPK. If you do throw whole fruits (with seeds) into the ground, expect to have some germinate – simply pluck them out and throw them back onto the soil, if you do not want to keep the plants they produce.

I always add some compost and fertiliser to the soil in addition to the kitchen waste (every month during summer, every two during winter).

Compost should be well degraded as to not burn the plants, so use ‘diluted’ add about half the volume of compost to the soil you want.

For granulated fertiliser – sprinkle on, DO NOT FOLLOW THE SUPPLIERS INSTRUCTIONS – USE LESS – a lot less – sprinkle a little bit only to dot about the ground, every two months. That should be enough, as fertilisers are synthetic and potent – so a little goes a long way. Rather use powdered fertiliser that is added to water, follow the supplier’s instructions for these as they are less potent and more "bioavailable" – can be used once a month to every two weeks without plant burn.

The fertilisers I use are:

2:3:2 NPK Granulated fertiliser (Cultura)
2.5:1:5 NPK Soluble powdered fertiliser (Starke Ayres Nutrifeed)

The Starke Ayres stuff is wonderful – the plants respond really well to this and can be used often (every two weeks for the tomatoes – cause they are hungry!).

I also add wood ash to my garden regularly as it contains a lot of potassium and other wonderful bioavailable nutrients for the garden... also used as cutworm control J

Update - 2017 - 

Please have a look at my series Sustainable, Productive & Economical Vegetable Gardening comprising of several articles in which I have expanded on my conservation agriculture principles in the garden:

            Part 1: Vegetables Worth Growing
            Part 2: Conservation Agriculture
            Part 3: Integrated Organic Gardening
            Part 4: Vegetable Garden Planting Guide & Management

Organic Composting Methods: Related Posts

Vermicomposting

Green Manures

Instant Compost

Comfrey: Organic fetiliser

Soil Profiles

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