Kitchen scraps can feed a garden, though not always in the way the tips suggest. Some household items are useful, some do very little, and nearly all of them work better through a compost bin than straight on the soil. This guide goes through the five most common ones and says what each does.
What works, and what is garden mythology
A lot of household fertiliser advice circulates without evidence. It is worth sorting, because some of it damages Australian gardens.
| Item | Verdict |
|---|---|
| Compost from kitchen scraps | Excellent. The best use of household waste |
| Worm castings and worm liquid | Very good, and easy to produce at home |
| Coffee grounds | Useful in compost. Do not use as a thick mulch |
| Crushed eggshells | Marginal. The calcium releases far too slowly to matter |
| Banana peels | Fine in compost; buried whole they just rot slowly |
| Epsom salts | Only where a magnesium deficiency has been identified |
| Diluted urine | Effective nitrogen, but not on natives |
| Milk, vinegar, sugar water | No credible benefit |
The five items, one by one
1. Coffee grounds
Used grounds contain a little nitrogen and improve soil texture once they have broken down. Add them to the compost as a green ingredient, or scatter them thinly and rake them in. A thick layer on the surface sets into a crust that sheds water, and fresh grounds can check seedlings. Our guide to the benefits of coffee grounds in plants sets out the limits.
2. Eggshells
Eggshells are calcium carbonate, and they break down over years, not weeks. They will not cure blossom end rot on tomatoes, which is nearly always caused by uneven watering and not by a shortage of calcium in the soil. Crush them finely and put them in the compost, where they do no harm.
3. Banana peels
Peels hold some potassium, which becomes available only as the peel rots. Buried whole beside a plant they decompose slowly and attract rats and fruit fly. Chop them into the compost or the worm farm.
4. Vegetable scraps
Peelings, outer leaves and tops are the backbone of a good compost heap. Dug straight into a bed they take nitrogen from the soil while they rot, so compost them first or bury them in a trench that will not be planted for a couple of months.
5. Tea leaves
Loose leaves are a mild green ingredient for compost. Many tea bags contain plastic fibre that never breaks down, so tear the bag and compost the leaves only.
Kitchen waste will not replace a balanced feed entirely, and our explainer on the science behind fertilisers covers what each nutrient does. How much difference any of it makes depends on what you are starting with, so identify your soil first; our guide to soil types explained shows how to tell sand from clay from loam in about a minute.
The rule that overrides everything in Australia
Do not use any of this on Australian native plants. Our soils are naturally very low in phosphorus and nitrogen, and natives evolved accordingly. Grevilleas, banksias, hakeas and waratahs are damaged or killed by ordinary nutrient levels because they cannot regulate their uptake.
Compost, coffee grounds, manure and household fertilisers all add nutrients natives neither need nor want. Keep them for the vegetable garden, citrus and exotic ornamentals, and use a certified low phosphorus native blend on natives or, in most cases, nothing at all.
Composting is where the real value is
Around a third of the average Australian household bin is food and garden organics, and in landfill that produces methane. Composting it at home turns the same material into the one soil improver that helps both sand and clay.
- Balance greens and browns: roughly one part nitrogen rich material (scraps, grass, coffee grounds) to two or three parts carbon rich material (dry leaves, shredded paper, cardboard).
- Keep it damp, not wet, like a wrung out sponge. In a Brisbane wet season, cover it; in a Perth summer, water it.
- Turn it every week or two for faster breakdown.
- Site it in shade in hot climates so it does not dry out.
- Keep it secure. Rats, bush turkeys and possums are all common visitors in Australian suburbs.
- No meat, dairy or oil in an open bin.
Many Australian councils now run food and garden organics collections, and a number offer subsidised compost bins and worm farms, which is worth checking before buying one.
Worm farms suit Australian conditions
They handle food scraps faster than a compost bin and produce both castings and liquid. Keep the farm in full shade: worms die above about 30°C, which is easily reached in an Australian summer, and a farm in afternoon sun will cook. Go easy on citrus and onion, and drain the liquid regularly, diluting it to the colour of weak tea before use.
What not to put on the garden
Do not use wood ash on Australian natives or acid loving plants. It is strongly alkaline and pushes the pH up, which locks out iron. Do not use fresh manure, which burns roots and can carry weed seed. And do not dump prunings in bushland or over a back fence, which is one of the main pathways by which garden plants become environmental weeds.
Preparing the ground properly at planting time matters more than anything you add later, as our guide on how to prepare the soil for planting explains, and our guide to green gardening and eco friendly practices extends the same thinking to water, mulch and pest control.
Common questions
Are coffee grounds good for plants?
In compost or raked thinly into soil, yes. As a thick mulch they form a crust, and they should be kept off natives.
Do eggshells stop blossom end rot?
No. Blossom end rot comes from irregular watering, which stops the plant moving calcium into the fruit. Water evenly and mulch.
Can I bury kitchen scraps straight in the garden?
You can trench them in a bed that will rest for a couple of months. Around growing plants, compost them first.
Ready to plant?
Kitchen scraps go furthest when they are topping up good soil, not rescuing bad soil. Stock up in our potting mixes, mulches and fertilisers collection, and put the results to work on a productive planting from our fruit trees range or the wider trees collection.
