Fertilizer is an important soil amender that supplies the vital macro and micronutrients plants need to grow healthy. Indoor and outdoor plants have different fertilizer needs, as indoor plants grow slower and need fewer nutrients. However, you still need to apply fertilizer to your indoor plants.
Here are a few ways to naturally fertilize indoor plants:
- Determine what nutrients your plants need.
- Decide on the right type of fertilizer for your plants.
- Time your fertilizer application well.
- Water your plants before fertilizing or repotting.
- Amend your soil’s pH to ensure nutrient release.
- Only fertilize your plants when necessary.
- Make your compost and compost tea.
- Mix crushed eggshells into your potting soil.
- Add used coffee grounds and tea leaves to the pot.
- Use bone meal for young or newly repotted plants.
- Add Epsom salts to the soil for magnesium.
- Bake and powder your banana peels for quick potassium.
- Fertigate with cooking water and broth.
- Buy a balanced natural fertilizer with OMRI certification.
- Dilute your fertilizer and use less than recommended.
- Apply your fertilizer to the soil evenly.
- Mix your fertilizer into the soil whenever possible.
In this article, I’ll explain all these steps and methods you can use to naturally fertilize your indoor plants and keep them fed and healthy for a long time, so read on!
1. Determine What Nutrients Your Plants Need
Fertilizers and pesticides are both necessary for overall plant growth.
Plants need several nutrients to help them grow, develop, and be productive, and fertilizers are used to supply these nutrients. These nutrients are broadly classified into macronutrients, secondary, and micronutrients, depending on the amount needed by plants.
The Three Key Macronutrients
Macronutrients needed by plants include:
These nutrients are typically labeled as NPK on commercial fertilizers and are found in varying ratios in different fertilizers. For the most part, a balanced ratio of NPK is useful, though plants may need different nutrients at different stages of their lives.
Nitrogen helps plants develop foliage and photosynthesis, where sunlight and water are utilized to transform nutrients into energy. Phosphorus is vital to the process of root development, which is especially important as root development is what ensures that plants can absorb nutrients from the soil.
Nitrogen and phosphorus are particularly important for crop plants and ornamental plants, as plants can only be productive if they have sufficient nitrogen and phosphorus.
Potassium is important to help plants uptake water from the soil and disperse it through the entire plant. As water is the medium through which plants can uptake nutrients, plants must have sufficient potassium, especially when using a lot of nutrients.
Plants like tomatoes need potassium-heavy fertilizers in the latter half of their fruiting season. The potassium helps the plants stay hydrated while consuming large amounts of nutrients, preventing fertilizer burn, which takes a long time and a lot of effort to fix in tomato plants.
Micronutrients play an important role in producing various amino acids and overall plant physiology. While these nutrients may be naturally present in garden soil, they may not be present in potting soil and must be supplemented with fertilizer.
Choosing a Fertilizer With the Right Nutrients
If you’re rooting your plants in garden soil, performing a soil analysis is a good idea to determine what nutrients your plants need.
For potting soil, you’ll have to add a balanced fertilizer with all the plant nutrients — macro, secondary, and micronutrients — to ensure your plants have everything they need to grow.
It’s also important to identify your plants’ growth stage. Newly repotted plants and seedlings need a phosphorus and nitrogen-heavy starter fertilizer to help them root faster.
You might need to alternate between phosphorus and potassium heavy fertilizers for your ornamental and fruiting plants. You might also need to apply a broader nitrogen-based fertilizer for the rest of the year.
The fertilizer you use will depend on the composition of your potting soil and the size of your plants.
Determining the right ratio of NPK and the micronutrients your plants need will help you holistically fertilize your indoor plants. That said, you can purchase NPK fertilizers at your garden store or online for your plants.
2. Decide on the Right Type of Fertilizer for Your Plants
There are several ways you can categorize fertilizer.
Inorganic fertilizers are synthetic and designed to supply plants with nutrients instantly unless they’re designed to be slow-release fertilizers.
All-natural fertilizers are slow-release, and the nutrients are released through microbial activity. On the other hand, organic or natural fertilizers are fertilizers derived from natural sources and produced through natural activity.
Types of Natural Fertilizers
Compost and manure are the most commonly known natural fertilizers, but several different natural fertilizers have their benefits. Most natural or organic fertilizers have a high percentage of nitrogen and are usually preferred for their additional benefits like improved water retention and overall soil quality.
Apart from compost and manure, there are different types of natural fertilizers like worm castings, fish emulsions, blood meal, bone meal, and kelp-based fertilizers. Different types of natural fertilizers can also be combined to feed your plants with the right ratio of nutrients.
Other Factors to Consider
Deciding the right type of fertilizer for your plants depends on the nutrients needed, the type of soil you’re using, the season, the immediacy of your plant’s requirements, and ease of use.
Seasons affect plant growth as most plants have a growing season, a time when they actively uptake nutrients and use them for growth and productivity. It’s essential to ensure that plants have the right nutrients accessible to them at different points of the growing season.
The immediacy of your plant’s nutrient requirements will determine whether you use liquid or solid fertilizers. Liquid fertilizers are easier for plants to uptake, which makes them good for immediate usage. Even if natural fertilizers are slow-release, liquid versions ensure that the nutrients are available to your plants faster.
When it comes to ease of use, liquid fertilizers tend to be easier to use since they can be distributed evenly or applied to the leaves directly if required. However, solid fertilizers can be mixed into the soil to improve the overall soil quality and feed your plants for a longer duration, even if they’re harder to handle.
The type of fertilizer you choose will depend on what your plants need.
3. Time Your Fertilizer Application Well
Timing your fertilizer application is important to ensure your plants have the nutrients they need when taking up and utilizing them.
Before the Growing Season
As I’ve mentioned, most plants have a growing season, which begins in early spring. During this season, plants can take up more nutrients from the ground as they utilize them to grow new roots and foliage, develop, and produce flowers and fruits.
However, natural fertilizers are slow-release, which means you need to incorporate the fertilizers into the soil well before the plants need them. This ensures that the microbes, soil pH, and moisture have enough time to break the fertilizers down and release the nutrients into the soil.
Before Going Into Dormancy
You could add compost, manure, or composted manure into the soil during fall, just before plants go into dormancy. As these natural or organic fertilizers are slow-release, they won’t build up in the soil and cause fertilizer burn.
During the dormant period, compost and manure disperse into the soil, attract organisms, and improve water and nutrient retention of the soil. Incorporating organic fertilizers into your soil this far in advance is a good way to ensure that you’ll need fewer fertilizer applications in the growing season.
When Preparing the Soil for Planting
Another time to apply fertilizer is when preparing the soil for planting. You can mix your natural fertilizer with your potting soil before placing your plants in, and this will supply your plants with enough nutrients for a few months.
Indoor vs. Outdoor Considerations
Indoor plants grow much slower than outdoor plants, so they need less fertilizer overall. But potting soil tends to have a high drainage capacity, so you might need to fertilize more often. Frequent fertilization is especially necessary for potted plants, as the limited soil means the nutrients get used up quickly.
It’s also important that you time your fertilizer applications so you’re not fertilizing them in the heat. This means you should avoid incorporating fertilizer when the days are very long and hot unless you supplement the additional nutrients with enough water to ensure uptake.
You should also avoid fertilizing your plants at midday and only add fertilizer in the morning or the evening when your plants are less likely to be heat-stressed. Plants can absorb more nutrients if they’re fertilized in the morning, especially if you’re feeding them with liquid fertilizer.
4. Water Your Plants Before Fertilizing or Repotting
Watering your plants before fertilization is essential to protect your plants from damage, particularly from fertilizer burn.
Plants need water for fertilizer and nutrient intake. The roots of your plants absorb nutrients from the soil suspended in water. The water is also used to disperse nutrients through the plant so it reaches the leaves, where they can be converted into sugars for the plant’s use.
Most fertilizers, even natural fertilizers, contain mineral salts. These salts are what supply the nutrients to the plant, but if they accumulate outside the plant, they draw the moisture out of plant tissue. The plant then gets dehydrated, leading to wilting, yellowing, and scorching of the foliage and roots in a process known as fertilizer burn.
Watering your plants is important because the right amount of soil moisture holds on to the nutrient. Water also gets the fertilizer wet so it can be dispersed easily through the soil and aids in breaking the fertilizer down to release nutrients.
Maintaining soil moisture at the appropriate level is important. If you see puddles of water in your pots, you’ve added too much water, and any fertilizer you apply will get washed away.
5. Amend Your Soil’s pH to Ensure Nutrient Release
Soil pH is often known as the master soil variable that affects the components and characteristics of soil and influences its nutrient makeup and fertility.
Soil pH is important for many reasons. But when it comes to fertilizing your plants, managing the soil pH is vital to ensuring nutrient release and availability. Nutrients are released from organic matter when they’re acted on by the acidic or alkaline nature of the soil.
The Link Between Macronutrients & pH Level
The macronutrients nitrogen and potassium, as well as the secondary nutrients like calcium, magnesium, and sulfur, are easily available in soils with pH values between 6.5 to 8.
On the other hand, phosphorus is more readily available to plants in mildly acidic soils with pH values between 6 to 7.
Raising & Lowering Your Soil’s pH
Depending on the nutrients your plants need, you should amend your soil pH to ensure that the nutrients will be available to your plants. Amending the pH is especially important if you need to ensure that the nutrients are made available to your plants quickly.
Natural fertilizers like compost and manure are useful for lowering the pH values of your soil by breaking up the soil particles and buffering them with organic matter. To increase the pH value of your soil and make it more alkaline, you can use lime or wood ash.
Wood ash is also a good source of potassium and calcium for plants and may also supply some phosphorus, so keep that in mind before you add it to your soil.
6. Only Fertilize Your Plants When Necessary
It’s vital that you only add fertilizer when your plants need it. Unused fertilizer, especially the more soluble ones like bone meal or fish meal, can lead to fertilizer burn, even if the fertilizers are organic or natural. High concentrations of plant nutrients in the soil can be more detrimental than helpful.
Risks of Overfertilization
Plants are rooted in potting soil rather than fertilizers because too much fertilizer can impede plant growth. If you supply plants with fertilizers when they don’t need them, the nutrients will only accumulate in the soil, leading to an unnecessary concentration of mineral salts and nutrients.
Plants that intake too much nitrogen, phosphorus, or potassium frequently show leggy growth, too much foliage, insufficient flowers and fruits, and general malaise. These plants may grow too quickly, making them vulnerable to disease and attacks from pests like mites and aphids.
Applying fertilizers when plants don’t need them, like midway through their dormant period, can also lead to fertilizer runoff and pollution. Unused fertilizer sits on the surface or drains into water bodies and groundwater, polluting it.
Nitrogen-rich fertilizers are particularly polluting. While natural fertilizers may not poison the water, they encourage the growth of algae which cover the surface of the water bodies and suck up all the oxygen.
With indoor plants, the excess fertilizer simply runs off through the drainage hole, and the wastewater may pollute nearby water bodies or groundwater sources.
Timing your applications to ensure that all the nutrients will be used up in time is crucial to ensuring that you don’t waste fertilizer and burn your plants with excess nutrients.
7. Make Your Compost and Compost Tea
Compost is one of the best natural fertilizers you can use to fertilize indoor and outdoor plants. It improves overall soil quality in many ways.
Compost is a great natural fertilizer because it:
- Aerates the soil by breaking up soil particles
- Improves water and nutrient retention as compost holds onto water well
- Balances the pH value of the soil by buffering the soil particles and making the soil more acidic
- Suppresses pests and plant disease because of the work of the microorganisms
Composting is a great way to use your organic waste and prevent it from releasing methane and other greenhouse gasses into landfills. The process itself is easy, and there are many ways in which you can make your compost, regardless of how small or big your household is.
Outdoor composting is ideally done in a box of at least three cubic feet (0.08 m3) to ensure sufficient volume for hot composting. This doesn’t mean you can’t compost in an apartment. Using smaller composting units or methods like vermicomposting or bokashi composting are all ways you can compost in small spaces.
You can also use compost to make compost tea, which is a liquid extracted by steeping complete compost in water. This liquid is not only useful as natural fertilizer, but it’s also a good pesticide when applied to the foliage and stems of your plants.
Making your compost and compost tea is a great way to use up kitchen scraps and supply your plants with the nutrients they need. You can also customize your compost tea by adding other fertilizers like fish emulsions to meet the specific needs of your plants.
8. Mix Crushed Eggshells Into Your Potting Soil
A great way of adding lime to your soil to neutralize the pH value to something more alkaline is by adding crushed eggshells into your potting soil.
Eggshells & a Calcium Boost
Crushed eggshells are a good source of lime and contain about 95% calcium carbonate, which is a great way to naturally add calcium to your soil. Calcium deficiencies lead to stunted growth in plants and discoloration in the leaves due to interveinal chlorosis.
Calcium is a difficult element to disperse through the leaf tissue, so watering your plants thoroughly until the water drains out of your pot should be the first step. If your plants still demonstrate a calcium deficiency, you can try adding crushed eggshells.
Plants fertilized with eggshell powder tend to grow taller than plants that haven’t received the additional calcium and pH amendment present in eggshells.
How to Make Your Soil More Alkaline With Eggshells
To use eggshells, they first need to be dried. You can leave them to dry in the sunlight or a low oven.
Once they’re dried completely, the eggshells can be ground to powder in a regular grinder. You can use up to 3 tablespoons (1.5 oz) of crushed eggshells in a pot, depending on the size and nutrient requirements of your plants.
Ideally, you should mix the eggshells with your potting soil or other fertilizer before placing your plants into the pot. If you need to add the eggshells in the middle of the growing season, work the powder into the first few inches (5+ cm) of soil after watering your plants to ensure good dispersal to the fine root hairs of your plants.
9. Add Used Coffee Grounds and Tea Leaves to the Pot
Coffee grounds and tea leaves are excellent sources of nutrients for your plants and can be used in many ways.
Apart from their nutritive benefits, both coffee grounds and tea leaves can be used to:
- Improve soil drainage
- Aerate the soil by separating the particles
- Neutralize soil pH values
- Provide mulch coverage allowing for improved water retention in hot weather
- Repel snails, slugs, and other pests from your potting soil
Coffee grounds and tea leaves are both good sources of nitrogen. They also have some amount of potassium and phosphorus, which can be supplied to plants slowly as they’re broken down.
Tea leaves also contain tannins, which benefit soil pH values and the soil’s ability to break organic matter down to release nutrients into the soil.
Applying Them to Your Soil
The best way to use coffee grounds and tea leaves is to sprinkle them on top of the soil. In humid weather, the grounds may attract mold. So you might want to use a rake and work the grounds and leaves into the first few inches (5+ cm) of soil to ensure there’s no unnecessary mold growth on top of your potting soil that might affect plant health.
Like all natural fertilizers, coffee grounds and tea leaves are slow-release. They’re best used as supplemental nutrition during the growing season as plants are preparing to flower.
10. Use Bone Meal for Young or Newly Repotted Plants
Bone meal is one of the best sources of phosphorus among natural fertilizers. It’s also a good source of calcium. Bone meal is great to mix in with compost, manure, or other nitrogen-heavy fertilizers to round out the nutrients supplied to your plants.
Phosphorus helps with root development, which is one of the most important functions of applying fertilizers to plants. Well-rooted plants can go deeper in search of moisture and nutrients and survive poor weather conditions like heavy winds and rains.
Bone meal is especially important for seedlings and newly repotted plants, as they need to grow roots quickly to survive and avoid transplant shock. Early root growth also ensures bigger yields in the flowering and fruiting season.
Methods for Using Bone Meal
Good bone meal is dried before grinding it down to ensure that it breaks down faster in the soil. Raw bones that are ground down will take longer to release nutrients into the soil.
Like eggshells, bones can be dried in a low oven or bright sunlight, though baking is an easier process. Commercial bone meal is made by steaming bones.
Apart from mixing bone meal with nitrogen fertilizers, it can also be used as a top dressing. This is especially useful for plants with limited or shallow root systems as the bone meal breaks down into the top few inches of soil, next to the fine roots of the plants.
11. Add Epsom Salts to the Soil for Magnesium
Epsom salts have many benefits for you and your plants. The salts themselves are the compound magnesium sulfate, which supplies your plants with the micronutrients they need to grow healthier and have larger yields.
Just about all types of plants do well with Epsom salts as fertilizers, from trees, shrubs, and lawns, to indoor plants that might not find sufficient magnesium and sulfate in their potting soil.
Epsom salts don’t accumulate in the soil as they’re water-soluble. If you’ve accidentally added too much, you can water your pots till the fertilizer drains out quickly. This water solubility also means that the nutrients are available to your plants for immediate use.
How Often & How to Use It
You can feed your plants with Epsom salts every month, using about two tablespoons for every two gallons (7.6 liters) of water. The salts should be applied to the root zone, around the drip line, and not too close to the base of the plant unless the plant is a rose or otherwise hardy.
Mixing Epsom salts in with your nitrogen-heavy fertilizers like manure is also a good way to make your own complete natural fertilizer for your indoor plants.
12. Bake and Powder Your Banana Peels for Quick Potassium
Banana peels are a fantastic natural slow-release fertilizer that supplies potassium to your indoor plants. They also contain nitrogen and phosphorus as well as several micronutrients, which makes them an excellent way to fertilize your indoor plants naturally. Consistent usage of banana peels helps plants grow bigger, yield more, and become disease resistant.
Depending on how much time you have, you can use banana peels as a natural fertilizer in several ways:
Dry Them Out & Powder Them
The fastest way to supply nutrients to your plants is to dry the peels out in an oven and powder them.
Cut your banana peels up into small pieces and bake them in a low oven on a baking tray. Once the peels have crisped up, you can grind them down into a coarse or fine powder as desired. Finer particles will ensure that your plants receive the nutrients faster, and the microbes in your soil will be able to break them down faster.
Banana peel powder is not water-soluble, so the soil pH and microbial action are what will release nutrients. If your potting soil is completely free of any actual soil, you might want to add at least a handful of compost or manure to introduce microbes into your mix. This will ensure that the organic matter of the peels will be broken down faster.
Make a Liquid Fertilizer
You can also make a liquid fertilizer by steeping banana peels in water in a covered container. After 2-3 days of steeping the peels, you’ll end up with a nutritious fertilizer that can be applied to the surface of your leaves.
A liquid banana peel fertilizer is useful when your plants need an immediate boost in potassium, as foliar applications supply the nutrients directly to the leaves. As the leaves receive the nutrients directly, you bypass the process of nutrient dispersal through the plant’s stem.
Foliar applications are a good way to supplement nutritional deficiencies while waiting on nutrient release from fertilizers mixed into the soil.
13. Fertigate With Cooking Water and Broth
Cooking water and broth made of bones left behind after making stock are great sources of nutrition for your plants. Cooking water left behind after cooking vegetables, rice, meat, or bones tends to carry some of the nutrients released in the heating and cooking process. These nutrients are great for plant growth and are an effective natural fertilizer.
Just as you can use your kitchen scraps in different ways that I’ve mentioned in this article to fertilize your plants, you can use the wastewater from your kitchens as well. This wastewater, also known as gray water, contains nutrients your plants can use.
It’s important to remember that cooking water and broth won’t supply a definitive amount of any nutrient. The minerals and nutrients present in the cooking water or broth will depend on the vegetables or meat cooked in the water. Generally, cooking water is a great way to supplement the micronutrients necessary for plant growth.
The water-soluble minerals will be easily absorbed by plants, which makes cooking water a great way of supplementing nutrition through more traditional fertilizers. It can be used during the growing season to support plant growth and reduce the amount of waste from your kitchens.
14. Buy a Balanced Natural Fertilizer With OMRI Certification
While you could make your own natural fertilizer by composting or using your kitchen scraps, you don’t have to. You can purchase natural fertilizers from the market. Most commercially available natural fertilizers are a mix of compost, manure, or composted manure with other natural fertilizers like kelp or fish emulsion.
All-natural or organic fertilizers will be labeled with the NPK ratio, so you know exactly how much nitrogen, phosphorus, and potassium you are applying to your plants. They may also have some secondary or micronutrients like sulfur, iron, calcium, and zinc unless the nutrient has been specified on the packet.
What Are Balanced Fertilizers?
Balanced fertilizers refer to those which have a more or less equitable ratio of NPK that supplies your plants with all the nutrients they need. These fertilizers are a good starting point to amend your potting soil with. As time passes, you can keep an eye out to see if your plants have any deficiencies and add additional fertilizers accordingly.
What an OMRI Certification Really Means
OMRI certification refers to a certification offered by the non-profit organization of the same name, which determines if the product is truly organic. As the term organic can be applied indiscriminately by manufacturers, an OMRI certification helps determine if the product is actually made of natural processes.
OMRI checks the fertilizers and ensures that it meets the standards in the Code of Federal Regulations for organic products. The certification is listed on the label as ‘OMRI Listed,’ which guarantees that the fertilizer is actually derived from natural materials through natural processes.
For example, you can grab a bottle of OMRI-certified fish & kelp fertilizer.
15. Dilute Your Fertilizer and Use Less Than Recommended
Even with natural fertilizers, it’s possible to use too much.
Excess fertilizer can have several detrimental effects on plants, including:
- Excessive foliage growth
- Reduced yield
- Growth that’s leggy and too quick
- Reduced resistance to disease and pest attacks
- Warped growth
- Fertilizer burn
Most commercial fertilizers come with a recommended amount. Using less than that recommended amount is better for your plants as you can see how effective the fertilizer is without burning your plants. Adding more fertilizer is much easier than attempting to rescue a plant suffering from fertilizer burn or excess fertilizer.
Diluting your fertilizers (especially liquid fertilizers like compost tea, manure, or fish emulsions) ensures that the nutrients are carried in a water medium and dispersed thoroughly.
Dilution ensures that the plants only get the nutrients they need rather than accumulating excess in the soil and that the available nutrients are taken up quickly.
Liquid mediums are the best way to apply fertilizers to indoor plants as they need low concentrations of nutrients supplied frequently. Liquid mediums are a great way to apply nutrients regularly in necessary quantities.
Diluted fertilizers are also easier to spread as they can be dispersed through the soil easily. This allows the nutrients to reach the deepest parts of the soil and the fine root hairs, which are sensitive and crucial for quick nutrient uptake.
16. Apply Your Fertilizer to the Soil Evenly
Even fertilizer application is necessary to ensure that plants can grow evenly and sustainably. If fertilizer is concentrated in any one area, the plant will send its roots out and focus on growth where the nutrients are most available. This results in lopsided growth that affects overall plant stability.
Applying fertilizer evenly is easier if your fertilizer is diluted or carried in a liquid medium. When it comes to solid fertilizers, you have to be careful to sprinkle the fertilizers over the surface in a thin, even layer before working them into the soil.
Use a rake or a tool to work the fertilizer into the top few inches (5+ cm) of soil evenly at about the same depth, as fertilizer that goes deeper will be accessed first by the roots of the plants. Be careful to apply fertilizer about an inch (2.54 cm) from the edge of the pot along the drip line of your plants.
Fertilizers applied too close to the base will be taken up first and might cause fertilizer burn on the uptake. Applying fertilizer close to the base only works if you’re supplying a starting solution to seedlings or newly repotted plants so they can grow roots out quickly.
The best way to ensure a uniform application of fertilizer is to measure out your fertilizer and mix it thoroughly with your potting soil, especially if you’re repotting your plants.
17. Mix Your Fertilizer Into the Soil Whenever Possible
Mixing your fertilizer into the soil is the best way to ensure an even supply of nutrients for your plants. Surface fertilizer applications are useful for supplementing immediate nutrient requirements during the growing season, but they have their limitations.
Fertilizers applied to the surface take a long time to disperse through the soil and be acted on by microbes, which delays nutrient release. As a result, only a small amount of powdered or liquid fertilizer can be applied to the surface to ensure proper dispersal and nutrient uptake.
The Best Time to Add Fertilizer
Ideally, you should work natural fertilizer into the soil just before the dormant period starts, in early autumn. Then you can mix the fertilizer into your potting soil before the growing season in early spring or whenever you repot your plants. With supplemental applications, working the fertilizer into the first few inches is sufficient.
Not only does it ensure good nutrient dispersal, but it also prevents mold growth and won’t attract any pests like flies because of the smell.
Naturally fertilizing your indoor plants is a simple process.
Here are a few key points that you should remember:
- Determine what nutrients your plants need and decide on the right type of fertilizer.
- Time your fertilizer application and always water your plants well before you apply any fertilizer.
- Make your own fertilizers at home with kitchen scraps and cooking liquid.
- Buy a balanced natural fertilizer with OMRI certification.
- Dilute your fertilizer before using it.
- Mix your fertilizer into the soil evenly.