Homemade Organic Fertiliser, What Actually Feeds a Pot (2026)

Last updated: 22 September 2026

> Quick Answer: The only homemade organic fertiliser that properly feeds a pot is a fermented oil cake feed, roughly 0.05% nitrogen. That is about 470 mg a litre as applied, against 160 mg for rice rinse water and nothing published at all for banana peel water. Eggshells supply calcium only, and coarsely crushed shell is close to inert.

Start with the number that settles most of the argument. Rape seed cake, the sarso khali sold as garden input across north India, is 5.2% nitrogen, 1.8% phosphate and 1.2% potash in the TNAU Agritech tables. Everything else on a kitchen counter is a rounding error next to it.

A feed, though, is not the material it came from. Soak 100 g of cake in a litre of water, dilute it before it goes near a root, and that 5.2% has become roughly 0.05%. That is the whole story of homemade fertiliser, and nobody writing recipes does the division.

Why is a homemade feed so much weaker than the recipe sounds?

Two dilutions happen and only one is visible: the water already inside the raw material, then the water you add.

Rice water shows the cost. A 2023 field trial measured washed rice water at 160.11 mg/kg total nitrogen, 90.92 mg/kg phosphorus and 118.11 mg/kg potassium, rising to 220.11 mg/kg nitrogen after three days of fermentation. A 15:15:15 mineral fertiliser is 150,000 mg/kg of each, so rice water is roughly a thousandth of it.

How do you make an oil cake liquid feed that works?

Weigh 100 g of milled mustard cake into a litre of water in a covered pot, stir, and leave it three to four days in the shade, a day longer in winter. Then dilute one part into ten parts water. Three details matter more than that recipe.

• Powder, not slabs. Cake leaves a press hard and microbes work on surfaces. A slab in a jar for four days is still a slab.
• Do not strain it. This is the one that quietly wastes the feed; the arithmetic is below.
• Cover it. Open fermentation in an Indian September invites fruit flies.

The jar is a nitrogen feed, not a soil improver, so it sits alongside compost rather than replacing it. For where each dry input belongs, see which garden input fixes what.

How much nitrogen does that feed actually carry?

About 470 mg per applied litre, which is arithmetic on the TNAU figure rather than an assay. Watch it happen: 100 g of cake holds 5.2 g of nitrogen, a 1:10 dilution makes about 11 litres, and 5.2 g over 11 litres is 473 mg.

Feed, as applied	Nitrogen per litre	Basis
Rice rinse water, as is	about 160 mg	Measured, 2023 field trial
Rice rinse water, fermented 3 days	about 220 mg	Measured, same trial
Cake feed, 100 g/litre, diluted 1:10, solids poured	about 470 mg	Calculated at 5.2% N
Cake feed, strained	well below 470 mg	Most N is protein bound
Banana peel soak	no published figure	Never measured
Crushed eggshell	none	Calcium only

Cake rows are arithmetic on a published average, not an assay of any bag.

Now the straining trap. Mechanically pressed mustard meal runs 34.9% crude protein, and protein nitrogen does not dissolve in four days; soil microbes release it over weeks. Pour the jar with its sediment and that protein mineralises in the pot. Strain it and you bin most of it.

Does banana peel water do anything for a pot?

It adds some potassium and essentially no nitrogen, and the dose is genuinely unknown. Potassium leaches readily because it is not chemically bound, unlike nitrogen locked in protein.

The published composition is a mess too. Review figures for banana peel potassium disagree by more than an order of magnitude depending on cultivar, ripeness and drying, and none measures what a soak extracts, which is the only number a gardener needs.

So it is not useless and it is not a feed. For the potassium, chop the peel and bury it, where all of it decomposes in place.

When do eggshells become available calcium?

Not this season, and not at all if you crushed them by hand. Eggshell is 94 to 97% calcium carbonate, genuine liming material, and the Iowa State trial that established it tracked soil pH across a corn and soybean rotation, not across weeks.

Particle size decides the rest. The same paper cites a greenhouse study finding finely ground shell effective and coarse shell essentially ineffective. Carbonate has to dissolve to work, dissolution happens at surfaces, and a half shell has almost none for its weight.

Two things follow for a terrace. Eggshell holds no nitrogen, phosphorus or potassium, so a hungry pot gets nothing at any grind, and the version that works is a flour, not a squeeze of the palm.

Which kitchen scraps do essentially nothing?

Rice water, tea water and used coffee grounds, at household quantities. Each has a real number behind it and each is too small.

Coffee grounds are the instructive one. Oregon State University Extension puts them at 1 to 2% nitrogen with a pH of 6.5 to 6.8, which kills the acidifying myth, and notes that uncomposted grounds have their nitrogen tied up first by the microbes breaking them down. Short term they remove nitrogen rather than add it.

Spent tea leaves behave the same way in smaller quantities, and compost extracts are no better: the WSU Extension review of the compost tea literature found published results variable and largely unreplicated.

None of that argues for binning the scraps, only for composting rather than steeping them. Compost is where a small quantity of weak material still counts.

What does a cake feed cost per litre?

A little over ₹2, which usually ends the argument for a terrace. SatRas mustard oil cake powder is ₹229 for 900 g on 22 September 2026, so one pack makes nine jars at 100 g each: about ₹25 a jar and roughly 99 litres of feed.

It is milled to powder rather than slabs, the form the jar needs, and it is cake left after SatRas presses its own mustard oil in a wooden kolhu, not solvent-extracted meal. That matters: solvent extraction drops mustard meal from 34.9% crude protein to 26.0%. For the price ladder, see what mustard cake costs per kg in India; for dry application, how much neem khali and sarso khali a pot needs carries the per-container quantities, and the four-input plant care set covers the rest.

Where a homemade feed runs out

Four limits, all of them real.

• No assay on any of it. Every nitrogen figure here is a published average for a category. Your bag was not tested, and pressed against de-oiled moves it by a quarter.
• Nitrogen is not all a pot runs out of. A cake feed is thin on potassium and carries no micronutrient guarantee.
• Liquid does not build soil. Potting mix collapses over a season and no jar fixes structure.
• The arithmetic is generous. It assumes complete mineralisation. Real release is partial and slow, which is the point of an organic feed and its ceiling.

Frequently asked questions

How long does a homemade liquid feed keep once it is made?

Use it within a few days. A fermenting jar keeps changing, and past roughly a week the smell turns as the microbial population shifts towards anaerobes. None of that harms a plant, but a jar left a month is not the material the recipe described. Mix small batches.

Are banana peels better buried in the pot than soaked in water?

Generally yes. Burying chopped peel puts the whole peel into the container, where it decomposes and releases potassium in place. A soak extracts only the soluble fraction, and no published study measures what that fraction is. Burying also avoids a jar of sugary water.

Do crushed eggshells stop blossom end rot in tomatoes?

Not reliably. Blossom end rot is usually a calcium delivery problem driven by uneven watering, not a shortage of calcium in the soil, so a slow carbonate rarely changes anything within a season. Steady moisture does more, and coarse shell reacts too slowly to matter to a fruiting plant.

Can a liquid feed replace compost in a container?

No. A liquid feed supplies soluble nutrients and nothing else. Compost supplies bulk, water-holding capacity, structure and a microbial population, which is what stops a potting mix collapsing into a dense block by season's end. They do different jobs and a pot wants both.

Does adding jaggery or sugar to the jar make the feed stronger?

It adds no nutrients. Sugar feeds microbes, which speeds fermentation and shifts the smell, but contributes no nitrogen, phosphorus or potassium of its own. If anything, a large sugar addition gives those microbes reason to hold nitrogen back rather than release it.

Is cow dung slurry stronger than a kitchen scrap feed?

Stronger than scraps, weaker than oil cake. Well-decomposed farmyard manure averages about 0.5% nitrogen in the TNAU tables, roughly a tenth of rape seed cake, so a dung slurry sits between rice water and a cake feed. Its real value in a pot is bulk organic matter, not the nitrogen.