Natural fertilizers are an environmentally-friendly and affordable choice that can help keep your indoor plants healthy and growing fast. Also known as natural plant food, these homemade fertilizers allow you to create nutrient-rich formulas using household items, resulting in a cost-effective DIY option. Whether you want a zero-waste process or just want to avoid harsh chemicals, these high-quality natural houseplant fertilizers will give your soil the nutrient boost needed to support long-term growth.
When making your own fertilizer, you can always add crushed eggshells for calcium, banana peels for potassium, coffee grounds for nitrogen, Epsom salt for magnesium and sulfur, green tea for increased acidity, wood ash for more alkalinity and molasses for general macro-nutrients. For quick absorption, a liquid recipe may be the perfect solution.
To inspire you, we’ve compiled a list of the best natural fertilizers for indoor plants. From green tea to cooking water, these simple homemade fertilizers will give your houseplants the nutrients necessary to grow naturally healthy and strong.
What Is A Natural Fertilizer?
A natural fertilizer is a plant, mineral or animal by-product that provides nutrients for plants to grow sustainably. These organic fertilizers generally break down slowly and deliver vital plant nutrients such as nitrogen, potassium, phosphorous, calcium, magnesium, iron and essential vitamins. The best homemade fertilizers for indoor plants are minimally-processed, cost-effective, easy to source and offer the right combination of nutrients.
How To Fertilize Houseplants Naturally
Creating your own fertilizer is a surprisingly simple way to tend to your houseplants in a cost-effective and environmentally-friendly manner. With a few common household items including kitchen waste, you can develop homemade fertilizer that is just as effective (if not more) than store-bought fertilizer.
There are two main types of fertilizer: organic and inorganic. Inorganic or synthetic fertilizers are commercially produced out of processed minerals, while organic fertilizers are made from living plant or animal sources. While you can purchase organic and inorganic fertilizers at retail locations like garden centers, a natural recipe made at home will always be a cleaner and safer choice.
The N-P-K Ratio Explained
If you’re interested in making your own organic fertilizer at home, the first thing you need to understand is the N-P-K ratio. This term refers to the nutrients nitrogen (chemical symbol N), phosphorous (chemical symbol P), and potassium (chemical symbol K). While multiple micronutrients are necessary for plant growth, these are inarguably the most important.
If you’ve ever shopped for store-bought fertilizer, you may have noticed that the N-P-K ratio is displayed on the bag. This indicates the amount of nitrogen, phosphorous and potassium contained by volume in a specific fertilizer blend as a series of three numbers.
If a 100-pound bag of fertilizer is labeled 12-12-12, that means it contains twelve pounds each of nitrogen, phosphorous, and potassium. If a bag of the same size is marked 6-8-4, it contains six pounds of nitrogen, eight pounds of phosphorous, and four pounds of potassium. The remainder of the bag contains filler that adds bulk and makes the fertilizer easier to spread.
It’s important to note that while all fertilizers will contain at least one of these elements, a particular formulation may be missing components. In that case, the ratio will display a zero for that nutrient.
Nitrogen, phosphorus and potassium each play a separate but equally important role in healthy plant growth. They break down as follows:
- Nitrogen: This nutrient is most heavily involved in the growth of foliage and stems. High-nitrogen fertilizers are ideal for leafy plants including hoya, monstera, and philodendron. Fertilizers that are high in nitrogen can also stimulate more rapid growth in the early stages.
- Phosphorous: This nutrient is crucial for the development of healthy root systems while amplifying the ability to produce blooms. Flowering plants like African violets, Madagascar jasmine, and peace lilies.
- Potassium: This nutrient is critical for virtually all aspects of plant growth and productivity and can make plants sturdier and more resistant to disease and insect activity. Potassium-rich fertilizers are often used for food-producing plants like fruit trees, zucchini, and tomatoes, but they are also appropriate for houseplants including tillandsia.
Popular Natural Fertilizers For Houseplants
Crushed eggshells are a great source of multiple nutrients, most predominantly calcium carbonate. Calcium carbonate is critical for strengthening the root systems and cell walls while also lowering soil acidity. Crushed eggshells are also a good source of magnesium, phosphorous, and potassium.
An unexpected benefit of crushed eggshells is their use as a pest deterrent. Slugs and snails have soft bodies that are easily punctured by the sharp edges of eggshells, while larger pests like deer are kept away by the residual aroma of eggs.
To incorporate eggshells into your fertilizer, start by saving any eggshells you use while cooking. Rinse the shells in warm water, leaving the membrane intact if possible to preserve the nutrients, and then let the shells dry completely before storing them in the freezer. An empty egg carton is a great place to store the broken shells until they’re ready to be processed. As a general rule, you’ll need about 4 to 5 eggshells for each plant you intend to fertilize.
Once you’ve accumulated enough eggshells, you can crush them into a fine powder. You can use tools like a food processor, rolling pin, or mortar and pestle. Be sure to wear a mask during this process, as it is easy to inhale fragments of eggshell. Finally, sprinkle the eggshells around the base. Over time, the calcium carbonate and other nutrients will leach into the soil and strengthen your plants.
We know that potassium is important to plant health as it is represented by the K in the N-P-K ratio. It so happens that bananas are one of the main dietary sources of this essential nutrient. Banana peels are also rich in potassium, as well as calcium, iron, and vitamins A and C.
There are several simple ways to use bananas as a fertilizer. First, you can place bananas in a jar and fill it with water. Let this mixture steep for a few days to allow the nutrients from the peels to infuse into the water. Then just use this nutrient-enhanced water to hydrate the soil around your houseplants.
If you don’t have time to wait for the banana peels to steep, you can also puree banana peels with water in a blender or food processor and pour the resulting mixture around the base of your plants.
Coffee grounds are full of nutrients essential to plant growth, including calcium, chromium, iron, magnesium, nitrogen, potassium, and phosphorous. In addition to enriching the soil, coffee grounds may play a role in absorbing the heavy metals that can contaminate soil. Finally, coffee grounds can attract worms which are valued by gardeners as their presence aerates the soil, leading to better drainage and increased nutrient availability.
To make high-quality organic fertilizer, start by spreading used coffee grounds out on a baking sheet. Next, dry them out by leaving them in the sun or baking them in the oven on low heat to keep the grounds from getting moldy. Finally, scatter the dried grounds on the soil surrounding your houseplants. A little goes a long way when employing this technique, so sprinkle the grounds sparingly. If you overdo it or allow the grounds to pile up, they can create a barrier that keeps water from penetrating the soil.
There is another popular method for transforming coffee grounds into fertilizer. Like banana peels, grounds can be infused with water. Pour two cups of used grounds into an empty five-gallon bucket, then fill the vessel with water and combine thoroughly before letting the mixture steep overnight. This nitrogen-rich blend can be spritzed onto leaves and stems to strengthen them, or added to the soil as a liquid fertilizer.
Many people drink green tea because of its many health benefits, and as it turns out, this popular beverage is equally advantageous for plant growth. Packed with nitrogen, phosphorous, and potassium, green tea hits the N-P-K ratio trifecta. Green tea leaves also contain other key nutrients including calcium and magnesium.
Because teas contain tannic acid, you’ll want to limit the use of green tea-based fertilizers to houseplants like azaleas and ferns that thrive in acidic soil. Plants that prefer neutral or alkaline soil won’t respond well to this organic treatment.
Like coffee grounds and banana peels, green tea is easily converted into a liquid fertilizer. Just soak used green tea bags in water and use that to water your houseplants, making sure to use cooled water instead of hot tea. As an alternative, you can cool down tea bags after use, and then cut them open and collect the loose leaves. Then sprinkle a thin layer of the leaves on top of the soil, almost like you would use mulch.
Molasses is a thick, sticky substance made from refined sugarcane that is often used to add sweetness or flavor to food. Packed with nutrients and micronutrients like calcium, copper, iron, and magnesium, molasses is highly beneficial to plants. In addition to providing a quick and efficient source of energy, molasses promotes fertility and deters insects and diseases.
To make a nutrient-rich molasses fertilizer, mix two tablespoons of molasses into a gallon of warm water. Unsulfured molasses is preferred, as sulfur can kill off important microbes. Put the mixture in a spray bottle and mist it directly onto houseplants, but don’t apply it more than once or twice per month. Otherwise, it can become too reliant on the fast energy boost.
Comprised of magnesium and sulfur, Epsom salts are a popular household remedy. Many people like to add a scoop of Epsom salts to a hot bath to help relieve muscle tightness and the pain associated with it.
Some gardeners believe that Epsom salts can also improve plant health, as their high concentration of magnesium could increase a plant’s ability to absorb nutrients like nitrogen and phosphorous. However, this assertion is still highly-debated in the world of horticulture.
If you’re a believer in the potential power of Epsom salts as a fertilizer, simply dissolve a small quantity of them in a spray bottle with water. Generally speaking, you’ll want to use one teaspoon of Epsom salts per gallon of water. Spray this mixture only on plants that are suffering from a magnesium deficiency since the solution can be harmful to other plants.
If you enjoy unwinding in front of a wood-burning fireplace, wood ash can be a great homemade fertilizer for your indoor plants. High in lime, potassium, and other trace elements, wood ash can help improve the health of your plants when properly applied. While wood ash from hardwoods like oak and birch will have the highest concentration of minerals and nutrients, ash from softwoods like can also add value.
Wood ash is most effective as a fertilizer when added to your compost bin. Though you can scatter wood ash directly into your soil, it can produce lye and salt when wet which may harm your plants. Composting the wood ash removes that risk.
Derived from collagen in the skin, bones, and connective tissue of animals, gelatin is an organic protein that is often used for culinary purposes. Because it is high in nitrogen, this inexpensive kitchen ingredient is also well-suited for use as a houseplant fertilizer. Chemical fertilizers containing nitrogen tend to break down very quickly in soil, which can weaken stems and foliage. Gelatin breaks down more slowly, reducing the risk of nitrogen buildup.
To make gelatin fertilizer, mix one packet of powder into a cup of hot water. You’ll want to use unflavored gelatin and not the sugary, fruit-flavored variety. Once the gelatin is fully dissolved, you can add three additional cups of cold water for a final ratio of about seven grams of powdered gelatin to one quart of water. Finally, pour the liquid fertilizer into the soil around your houseplant. You can use this fertilizer about once per month for the best results.
Used Cooking Water
When we boil foods like eggs, grains, legumes, and vegetables, nutrients like calcium, nitrogen, and phosphorous are released in the cooking water. Instead of pouring these valuable minerals down the drain, you can use the leftover cooking water to nourish your houseplants.
Not only will this provide an immediate nutritional boost, but it will also improve your soil’s ability to retain moisture over time. This quality makes used cooking water the ideal fertilizer for moisture-loving plants like crotons and calatheas.
Of all of the homemade organic fertilizer options, used cooking water is probably the easiest to use. Once it has cooled down, you can use cooking water to fertilize your plants with no additional processing. It is important to note though that not all cooking water is good cooking water.
Heavily salted water will harm plants more than it will help them. Conventionally-grown produce may also harbor hazardous pesticides, so stick to recycling water that was used to boil organic produce only.
Corn Gluten Meal
Many homemade fertilizers include household byproducts like cooking water and coffee grounds. Corn gluten meal is an industrial byproduct that results from the wet-milling of grain. Because it is high in protein, corn gluten meal is often used as filler in feed for animals like pets, poultry, and livestock.
In recent years, it’s also become popular with home gardeners as an organic pre-emergent herbicide. Though its efficacy in that realm is under debate, its high percentage of nitrogen makes it an excellent organic fertilizer.
Despite the similarity in names, corn gluten meal is not interchangeable with the ground cornmeal you can find at the grocery store. However, you can pick it up at most stores that carry plant supplies. Once you’ve purchased corn gluten meal, you can dust a thin layer over the surface of the soil and then blend it in carefully, being careful not to disturb the roots.
Aquarium water is filled with ammonia, nitrogen, phosphorous, potassium and other trace nutrients that promote good plant health. While fish need to be in clean water for optimal health, this dirty water also also contains organisms that, while harmful to fish, are beneficial to plants.
It’s important to note that not all aquarium water is suitable for use as a fertilizer. If you have a saltwater aquarium or if you’ve been a little lax about changing out the water in your fish tank, you should steer clear of your plants with it.
Even when filtered and maintained, aquarium water should only be used on ornamental plants and not edible ones due to the risk of chemical contamination. Under the right circumstances, using aquarium water can be a nutrient boost for your houseplants.
Benefits of Homemade Fertilizers
While fertilizer is mostly purchased by farmers, home gardeners also make up a significant amount of the market. As fertilizer prices continue to rise, even the small amount required for houseplants can be quite costly.
Many of the ingredients used to make homemade fertilizers are the byproducts of other household items. If you’re already buying eggs to cook with, you can save money by incorporating this natural ingredient into a fertilizer, creating a zero-waste process.
Safe and Organic
While organic homemade fertilizers are made from nontoxic goods found around the house, inorganic store-bought fertilizers are made up of minerals and synthetic chemicals. Certain ingredients found in inorganic fertilizers are poisonous when swallowed, making them dangerous to pets and small children.
Chemical fertilizers often contain heavy metals including lead, mercury, and cadmium which can cause health problems after prolonged contact. Many studies indicate that exposure to chemical fertilizers may increase the risk of cancer in both children and adults. There is also a more pressing danger to take into consideration. Ammonium nitrate, which is a key ingredient in many fertilizers, is highly combustible under the right circumstance.
While it may take some effort and time, making your own fertilizer at home can be a great investment that results in healthy and beautiful indoor plants. There’s also something comforting in knowing exactly what ingredients are contained in your organic fertilizer. Homemade organic fertilizer can even enrich your soil and improve it over time, offering an environmentally-friendly option for conscious gardeners.
Environmentally-Friendly and Sustainable
We already know that synthetic fertilizers can cause health issues in humans, but they can also be detrimental to the environment. While fertilizers are used to promote plant growth, overuse can reduce soil fertility in addition to attracting pests like aphids and mites.
But the harmful effects of fertilizer aren’t restricted to your own home and yard. Chemical fertilizers contain substances like ammonia, carbon dioxide, and methane, all of which contribute to the rising levels of greenhouse gas levels thought to be behind global warming.
Excess fertilizer is also frequently washed away from lawns by rain, which can cause runoff into waterways, lead to the growth of algae blooms and potentially harm aquatic life.