A banana peel is loaded with potassium. An eggshell is mostly calcium carbonate. Neither one does much sitting in landfill, but steeped in water for a week or two, they turn into two of the cheapest liquid feeds I make in my own garden.
What You Need
I keep this dead simple. No dehydrators, no blenders, no special kit.
- 2 to 3 banana peels (skins only, the fruit’s for eating)
- 4 to 6 eggshells, rinsed
- A 2 litre jar or an old ice cream tub with a lid
- Tap water, left out overnight if yours is heavily chlorinated
- A second jar, because I run peels and shells as separate brews
The Method
I keep banana peels and eggshells apart because they feed different things and I want control over the dose of each.
- Chop the banana peels into rough chunks and drop them into a jar. Cover with water, seal, and leave on the bench out of direct sun.
- Give it a shake once a day. After 5 to 7 days it’ll smell faintly sweet and a bit fermented. That’s your potassium feed, ready to strain.
- For the eggshells, crush them first. The finer you crush, the faster the calcium leaches out. A rolling pin over a tea towel does the job.
- Cover the crushed shells with water in the second jar and leave for a full 2 weeks. Eggshells are slow. Rush this step and you’ll get shell grit in water, not a usable feed.
- Strain both brews through an old sieve or a scrap of shade cloth before use. Compost the solids or toss them straight back onto a bed.
In the tropics and warm subtropical zones, the banana peel brew ferments faster, sometimes in 4 days over summer, so check it early or it’ll turn properly sour instead of just yeasty. In cool temperate and cold zones over winter, give it the full week, and don’t be surprised if it takes closer to 10 days on a cold bench.
How to Use It
Both brews are strong enough that they need cutting before they go anywhere near a plant.
- Banana peel water: dilute 1 part brew to 10 parts water. Use it on flowering and fruiting crops, tomatoes, capsicum, chilli, zucchini, anything that’s just set fruit and needs the potassium to fill it out. Water it in at the base every 2 weeks.
- Eggshell water: dilute 1 part brew to 5 parts water. I save this one for tomatoes and capsicum copping blossom end rot, and for brassicas early in their run. Once a fortnight is plenty.
- Don’t tip either one on seedlings at full strength. Both will burn young roots.
The Payoff
Neither brew replaces a proper balanced fertiliser. What they do is patch two specific gaps, potassium for fruit fill and calcium for cell strength, using scraps that were already headed for the bin. I reckon that’s a bottle or two of specialty feed I’m not buying each season, for the cost of a jar and a bit of patience. Once you’ve got a rhythm going, keep a jar brewing at all times so there’s always a batch ready when the tomatoes start setting fruit.
The only real downside is remembering which jar is which before you water. I’ve dosed a tray of seedlings with full strength eggshell brew by mistake once, and it was not a good week for that tray.
