Mustard Cake (Sarson Khal), Wood Ash and Gobar for Plants

“Thori si raakh daal do, aur khal bhigo ke do.” It’s advice every desi gardener has heard, and it’s mostly right, with conditions. Mustard cake (sarson khal) is a strong, smelly nitrogen feed; chulha ash is a potassium-and-lime sprinkle that suits some pots and hurts others; and gobar is gentle, excellent food only once it’s properly aged. This guide puts the three side by side, with pot amounts, the fermented khal method, and the safety rules nobody mentions.

Sarson khal, raakh and gobar compared

They aren’t rivals. Many good home gardeners use gobar compost as the base in the potting mix, sarson khal as the monthly feed in the growing months, and ash only now and then for fruiting plants.

Mustard cake fertilizer: dry and liquid

Sarson khal is the pressed cake left behind in the kohlu after mustard oil comes out. Nurseries sell it as flakes, lumps or powder. It’s one of the richer natural nitrogen sources a home gardener can buy, which is why roses and lemons respond to it so visibly. It’s also used as cattle feed, so a clean, dry, fresh-smelling bag is what you want. A musty or mouldy one goes straight back.

Dry use

Crush it to a coarse powder. Scrape the top 2 to 3 cm of soil aside, sprinkle 1 level tablespoon evenly around a medium pot, well away from the stem, cover it and water. Once a month in the growing months (roughly February to April and September to November in most of Pakistan and north India) is enough. It works slowly and can draw ants and fungus gnats if it’s left on the surface, so always cover it.

How to make mustard cake liquid fertilizer

1. Weigh: about 100 g of crushed khal (a small fistful) for 1 litre of water.
2. Soak: in an old bucket or bottle with a lid that sits loosely, so gas can escape. A tightly capped bottle can bulge or burst.
3. Wait: 3 to 5 days in summer, up to a week in winter, stirring once a day with a stick. Keep it in shade and outdoors if you can.
4. Expect the smell: it will be strong and sour. That’s normal. Fuzzy coloured mould on top means throw it out.
5. Dilute: 1 part of the liquid to 10 parts water. A 250 ml cup of khal liquid makes about 2.75 litres of feed.
6. Pour on damp soil: 250 to 500 ml per medium pot, never on leaves, never on dry soil.
7. Repeat: every 2 to 3 weeks in the growing months. Skip it in 45 °C heat and in deep winter, when plants rest.

The leftover sludge can be buried in a big pot or added to compost. Wash the bucket and turn it upside down so it can’t collect rainwater.

Why never on seedlings? As mustard cake breaks down it releases sharp compounds that can stop seeds sprouting and burn tender young roots. Give an established plant only, and wait about two weeks after dry khal before sowing seeds in that pot.

Wood ash for plants: chulha raakh done right

Ash from a wood chulha, dry leaves or uple (dried dung cakes) holds the potassium and calcium the fuel had, and almost nothing else. It’s the original “pot ash”: the word potassium comes from potash, ash soaked in pots to make lye and soap. That tells you the first safety fact. Wet ash is caustic. It can sting skin and badly irritate eyes.

The rules for ash

• Only clean fuel: untreated wood, twigs, leaves, dung cakes. Never coal, charcoal briquettes, barbecue lighters, plywood, painted or polished wood, cardboard with print, or anything with plastic in it. Those ashes can carry metals and chemicals into food plants.
• Cold and sifted: let it cool fully for a day, then sieve out chunks.
• Gloves on, nose covered: don’t breathe the dust, keep it off your face, and never let children play with it.
• Soil, not leaves: mix 1 level teaspoon into the top soil of a medium pot, then water. Ash on leaves burns them.
• Not every two weeks: once every 2 months at most, and only for plants that like it.
• Not with other feeds at once: keep ash a week apart from fresh gobar or urea, as the mix releases ammonia and wastes the nitrogen.

Is wood ash good for all plants?

No, and in many Pakistani and north Indian homes it’s needed less than people think. Ash raises pH. Much of the soil across the Indus and Gangetic plains is already alkaline, and hard tap water pushes pots further that way. More alkaline soil locks up iron, which is why curry leaf, lemon and rose often get yellow leaves with green veins. So chillies and tomatoes at flowering can take a pinch; lemon a little, rarely; curry leaf and pots with a white crust on the soil, none.

Cow dung fertilizer for plants: only when it’s aged

Fresh gobar is too strong for pots. As it rots it heats up and releases ammonia, which burns roots, and it carries gut germs such as E. coli, fly eggs and weed seeds. It also smells, which neighbours on a shared balcony won’t thank you for.

Aged gobar is a different thing entirely. After at least 3 months (6 is better) in a heap that’s been kept damp and turned, it becomes dark, crumbly, cool to the touch and smells like soil. That’s gobar khad, and nurseries sell it bagged.

How to use it

• At potting: 1 part aged gobar to 3 or 4 parts soil and sand or cocopeat.
• As a top-up: 1 cup spread on top of a medium pot every 1 to 2 months, then water.
• Dry uple: sun-dried dung cakes aren’t composted, just dried. Crush and compost them first, or use their ash as above.
• Edible leaves: keep it on the soil, not on leaves, and wash herbs well before eating.

A simple test: if you can still see straw bits and it smells like a cattle shed, it isn’t ready.

Where each fits: lemon, rose, chillies and curry leaf

• Lemon (nimbu): aged gobar in the potting mix, sarson khal monthly from late winter to autumn, a teaspoon of ash only once or twice a year. Lemons are hungry, so a nursery citrus feed often earns its place too.
• Rose: the classic khal plant. Liquid khal every 2 to 3 weeks from bud to bloom, gobar compost twice a year. Skip ash if the soil already crusts white.
• Chillies (mirch): gobar in the mix at planting, then a pinch of ash and some khal when the first flowers appear. Too much nitrogen early gives leaves and few chillies.
• Curry leaf (kari patta): aged gobar and compost, khal lightly now and then, no ash. It prefers soil on the less alkaline side. The full curry leaf growing guide covers sun, winter care and pruning.

Tulsi does well on gobar compost alone; heavy khal gives soft, leggy growth. The tulsi guide has the rest. More pot-feeding ideas live in the Zero-Waste Kitchen section.

Mustard cake, wood ash and cow dung: questions people ask