Homemade Fertilizer for Cannabis: 9 Free DIY Recipes

You can make solid homemade fertilizer for cannabis from kitchen scraps and household leftovers: used coffee grounds, banana peel tea, wood ash, brewer's yeast, bean water, eggshells, worm castings, veggie cooking water and even diluted urine. Grow shops sell plenty of nutrients, but what's already in your house can give your plants a real boost for free.

That way you can run a top-shelf cannabis grow without paying for brand-name nutrients: you make your own, naturally and 100% eco-friendly.

Homemade fertilizers for cannabis

Coffee grounds

Used coffee grounds are a classic homemade cannabis fertilizer: if you brew a cup in the morning, save the grounds and mix them into the soil. Coffee's acids help beneficial bacteria thrive, and those microbes help your plants grow strong. You can also use leftover brewed coffee: dilute half a cup in 1 liter (about 1 quart) of water and let it sit for 24 hours. Use this mix to water the soil once a week.

Banana peel tea

Banana peel tea is a potassium-rich homemade feed, and almost everyone has bananas at home, so save the peels. How do you make banana tea for plants? The recipe: boil 1 liter of water with 3 banana peels and a tablespoon of sugar. Boil for about 10 minutes, let it cool, take out the peels and use the liquid to water your plants and load them up with potassium and amino acids. Banana peel tea is meant for flowering: growers swear by it as a homemade way to fatten up buds. You can start using it during the last six weeks of flowering.

That's why the recipe calls for sugar, a popular homemade trick for bulking up buds; if you're out of sugar, use honey instead. These are the go-to homemade boosters for bigger buds.

Wood ash

Wood ash from a fireplace or wood stove works as cannabis fertilizer, so when winter rolls around, don't toss it.  Two things to keep in mind: the wood should come from broadleaf (hardwood) trees, and the ash is best used during flowering. It has to be pure wood ash, and you should store it for a week in a dry place before mixing it into the soil.

You can also make a mix by diluting half a cup of wood ash in 1 liter of water and letting it sit for a few hours, or combine coffee and ash. Then water your cannabis plants with it to boost potassium and phosphorus. Go easy, though: wood ash is very alkaline and raises soil pH.  

Remember, this is one of the best homemade fertilizers for cannabis plants in flower.

Brewer's yeast

Heads up: brewer's yeast isn't the same yeast you use to bake bread. Brewer's yeast is rich in minerals, amino acids and protein, and it's a multipurpose fertilizer. To use it, dissolve a tablespoon of brewer's yeast in 1 liter of water. Your plants will get a load of phosphorus, potassium and minerals, ideal for the flowering stage.

Bean or lentil water

Bean water is an organic cannabis fertilizer that's great for roots, since legumes are packed with auxins (natural plant hormones that drive root growth).  To make it, soak a cup of legumes, like beans or lentils, in 1 liter of water for a day. Warm the legumes up a bit in their soaking water, then strain out the liquid. Water with it and your roots will go wild.

Legumes are known as highly nutritious seeds, and they've become popular for boosting plant growth, root development and even the way plants stretch toward the light.

Eggshells

Eggshells are one of the most natural cannabis fertilizers out there. They're mostly calcium carbonate, so they work as a slow-release source of calcium, plus small amounts of other minerals, and that makes them excellent for feeding your plants.

Worm castings

Worm castings (worm humus) are, along with eggshells, one of the best homemade fertilizers for cannabis. They're especially good during the vegetative stage.

You make worm castings by putting organic scraps in a compost bin with red wiggler worms, which eat the scraps, break them down and turn them into a soil-like manure that's pure gold, loaded with N, P, K, Fe, Mg, C, Zn, B, Cu, Mn, auxins, and humic and fulvic acids.

Water from cooking spinach and other veggies

When you steam or boil spinach (and plenty of other vegetables), a lot of their nutrients end up in the water. Once it cools down, you can use it as part of your regular watering to add potassium, calcium and iron.

Urine

It might sound gross, but human urine belongs on this list of homemade cannabis fertilizers because, when it's fresh, it's a decent, non-toxic source of nitrogen, phosphorus and potassium. Nitrogen is the most useful part, which makes it another good liquid fertilizer for the vegetative stage. Urine has to be heavily diluted before it goes into your growing medium; never apply it straight.

What nutrients does cannabis need in veg and flower?

In the vegetative stage, cannabis plants need high levels of nitrogen, which they use to build plenty of healthy leaves and stems, plus medium levels of phosphorus, which they need for a strong root system.

Keep up this feeding plan during the first weeks of flowering too, to get through the “stretch,” the stage when plants need a lot more nitrogen. Once flowering is in full swing, keep nitrogen low and bump up phosphorus, since that's what drives heavy flowering and bud production.

Potassium is needed at every stage, but especially during flowering, ideally at twice the nitrogen level. That's because phosphorus increases the number of buds, while potassium increases their size and weight.