At last, you have a beautiful indoor garden and you want to make sure your indoor plants have everything they need to grow. Plants need nutrients to grow beautiful flowers, lush green foliage, strong roots and help fight diseases. So, if you’re looking for the best fertilizer for indoor plants, we can help.
Unlike in an outdoor garden, where it rains, the sun shines and your plants can grow new roots to search for food and water, the nutrients available to indoor plants are limited to the soil in their pot. Therefore, supplementing their soil using a good quality fertilizer is essential.
The right fertilizer will complement the energy from the sun and the nutrients in the soil to make sure your plants have everything they need. Too many people overlook the importance of fertilizing indoor plants. However, a proper routine of fertilizing your indoor plants is essential to ensuring sustainable, healthy, beautiful plants.
When your plants are new or recently re-potted, your plants don’t need much (if any) additional fertilizer. If you have just purchased your plant from a garden centre, it is unlikely that it will need to be fertilized immediately. However, after a period of time (6 – 8 weeks), your plants have consumed most of the nutrients in the soil and you will need to start thinking about fertilizing.
The real secret to fertilizing indoor plants is to provide small amounts of fertilizer as your plant grows.
If your indoor plant is not actively growing, it doesn’t need fertilizer. That is, if it is winter, or during periods of limited growth, you don’t need to fertilize your plant. However, if your plant is actively growing it needs help supporting its growth. So, during summer, or when the light and temperature increases, you need to fertilize your plant.
There are hundreds of fertilizer products available to gardeners. And, many are specially formulated for indoor gardening. But, choosing one and knowing how to use fertilizers can still be confusing.
So, what is the best fertilizer for indoor plants, when and how often should you fertilize your indoor plants, and finally how do you fertilize indoor plants. We want to provide you with all the answers so you can be confident knowing that you are using the best fertilizer for your indoor plants.
Not every indoor plant is the same. Believe it or not, they all have different personalities and needs, like humans! So, you need to get to know your indoor plant and adjust your approach to feeding it accordingly.
But, before we think about feeding your indoor plants, let’s think about the following:
- Plant Type: Some of your plants will be heavy feeders (e.g. Ficus) while others are not and will not need additional fertilizer for months (e.g. succulents).
- Volume of Soil: Smaller pots will require less fertilizer than your larger pots.
- Light Levels: the more light your plant enjoys, the more nutrients your plant also need to support growth.
Which type of fertilizer is best for indoor plants?
Finding the best fertilizer for your indoor plant can be tricky because there are so many different types available.
Let’s firstly look at the different types of fertilizers – liquid, granular and slow release, and how each type of fertilizer works.
Liquid Fertilizer
Liquid fertilizers for indoor plants are usually added to water and applied at regular intervals (sometimes every time you water, sometimes at every other time you water). Some formulas are only applied to your plants once or twice a month.
These types of fertilizers provide a steady supply of nutrients that you can fairly precisely control such as more when the plant is actively growing and less when the plant is not actively growing. However, if you use liquid fertilizers, you need to remember to add the fertilizer to the water at regular intervals. Perhaps noting these on your calendar might help.
Granular Fertilizer
Granular fertilizers are dry pellets that are mixed into the soil. They are especially useful when first potting or repotting an indoor plant because you can mix the fertilizer evenly throughout the soil. Granular fertilizers are clean to handle with no mixing. However, granular fertilizers dissolve when your plant is watered making it very hard to control the release of nutrients over a longer period.
These types of fertilizers are inexpensive and frequently used outdoors but are not really a good choice for fertilizing indoor plants.
Slow-Release Fertilizer
These types of fertilizers have quickly become a favourite for indoor gardeners. There are various forms of slow release fertilizers – spikes, rods, pods and pellets – all of which slowly release the nutrients using time release coatings that slowly dissolve. Slow-release fertilizers are a great choice for small pots giving you confidence that over fertilization is not happening. However, there is no real way of knowing how quickly the nutrients are dissolving other than relying on the information provided by the manufacturer.
Slow-release fertilizers can be expensive but last much longer than the other types of fertilizers.
Organic versus Non-organic Fertilizers
Organic fertilizers are those that are made from natural ingredients. These fertilizers are broken down and release nutrients when the soil is warm and moist. Organic fertilizers often have lower concentrations of nitrogen, phosphorous and potassium, so you will need to use more. But, organic fertilizers are slower to release their nutrients reducing the risk of over-fertilization. They are generally a gentler form of fertilizer and often contain many other beneficial nutrients that feed plants.
In contrast, non-organic fertilizers provide nutrition in form that your plant can immediately use. However, this rapid release of nutrients increases the risk of burning the roots of your plant.
If you opt for a non-organic fertilizer, you should also think about adding some organic matter to your indoor plants, such as compost or manure, to increase overall soil health. Obviously, you need to be careful what you are using indoors because some organic matters may also feature an offensive odour.
So, in summary:
Type | Pros | Cons |
Liquid | Lots of control over the release of nutrients Can suspend feeding during winter or dormant periods | You have to remember to add the fertilizer (at the appropriate intervals) when watering |
Granular | Simple to use Inexpensive Effective when mixed into the soil when potting a plant | Uneven distribution of nutrients through the soil. No control over the release of nutrients |
Slow Release | Simple to use Releases nutrients into the soil over a period of time | Higher cost, but lasts longer Sometimes uneven distribution of nutrients through the soil (mainly sticks) No control over the release of nutrients |
Organic | Made from natural ingredients Gentler on plants Contain other nutrients beneficial to plants | Slower to release nutrients Lower levels of required nutrients so may need to use more than non-organic types |
Non-organic | Manufactured artificially and contain minerals or chemicals Start releasing nutrients immediately | Risk of over fertilization or burning the roots of your plant Need to supplement soil with other organic material |
In my opinion, the best fertilizers for indoor use are liquid and slow-release because they are both convenient and allow you to control the release of nutrients. I would recommend organic fertilizers because there is less likelihood of burning the roots of your plant and these are very natural fertilizers for indoor plants.
Important!
Always follow the instructions on fertilizer labels. Too much fertilizer can kill a plant or scorch its leaves and too much fertilizer is often worse than not enough. Many well meaning indoor gardeners over water and over fertilize their indoor plants.
Macro and micro-nutrients: How important is nutrient make up?
All fertilizers for indoor plants contain the same basic macronutrients that plants need to grow, including nitrogen (N), phosphorus (P), and potassium (K) and are often referred to as NPK.
Each macronutrient has a specific function:
- Nitrogen encourages healthy foliage growth.
- Phosphorous encourages the production of flowers, seeds and fruit and is essential for healthy root growth.
- Potassium encourages a strong root system and helps with the production of fruit too, and it also gives plants their ability to resist disease.
In addition to these macronutrients, better-quality fertilizers also contain micronutrients such as boron, magnesium, and manganese that will encourage healthier growth.
There are also many specially formulated fertilizers on the market that address the optimum nutritional requirements of certain types of plants (e.g. orchids, indoor vegetables, african violets, etc). These are worth using if you have indoor plants with special needs.
How do I read the nutritional information?
So, now you understand the types of fertilizers and the macronutrients that indoor plants need to thrive. But how do you know what each bag or bottle contains? There are labelling standards that all manufacturers must follow. These are helpful in comparing fertilizers.
Remember the acronym NPK. Most fertilizers display a three-part number, something like 5-10-5, on the package. This measurement refers to a percentage of three major nutrients (nitrogen, phosphorus and potassium) in the fertilizer.
As an example, one of our recommended fertilizers for indoor plants says 6-12-6 on the label. It therefore has a composition of 6% nitrogen, 12% phosphorus and 6% potassium and the rest of the fertilizer will be minor nutrients and fillers (in this case 76%).
For indoor plants, fertilizers with balanced nutrient ratios (4-4-4 or 10-10-10) or 1:2:1 ratios work best (10-20-10 or 6-12-6) but others with different ratios are just fine.
Best fertilizer for indoor plants – our top 8
There are a lot of different types of fertilizers and the composition of each fertilizer may be different, so we have shortlisted some of the best fertilizer for indoor plants options for you:
| Name of Fertilizer | Type/ Nutritional Composition | Other Information |
|---|---|---|
  Jobe's 5001T Houseplant Indoor Fertilizer Food Spikes, 50 Pack(2) | Slow Release 13-4-5 | Lasts up to 2 months Pre-measured spikes are simply inserted into the soil around your plant No mess, hazards or smells |
  Miracle-Gro Water Soluble All Purpose Plant Food, 10 Lb | Granules 24-8-16 | Lasts 1 - 2 weeks For indoor plants simply add to the watering can |
  Osmocote 274150 Smart-Release Plant Food Plus Outdoor & Indoor, 1 LB | Slow Release 15-9-12 | Lasts up to 6 months Very versatile fertilizer, can be used indoors and outside Mix the pellets into the soil at the top of the pot and water regularly Contains 11 essential nutrients |
  Miracle-Gro Indoor Plant Food, Fertilizer Spikes, 2.2 Ounce (2 Pack)  | Slow Release 6-12-6 | Lasts up to 2 months Simply make a small hole in moist soil and insert the plant food spike |
  J R Peters Inc (52064) Jacks Classic No.4 20-20-20 All Purpose Fertilizer | Liquid 20-20-20 | Lasts up to 4 months Especially good for foliage plants For indoor plants simply add to the watering can |
  Espoma PT4 4-Pound Plant-Tone Organic 5-3-3 Plant Food | Organic Slow Release 5-3-3 | Lasts up to 4 weeks Mix into the soil 15 essential nutrients Enhanced with bio-tone beneficial microbes. |
  Miracle-Gro Performance Organics All Purpose Plant Nutrition Granules, 2.5 lb. - All-Purpose Plant Food - All-Purpose Formula for Vegetables, Flowers and Herbs - Feeds up to 240 sq. ft. | Organic Granules 9-2-7 | Lasts up to 6 weeks Mix into soil and water Fast results in as little as 7 days Shaker jug makes for easy application |
  Liquid Indoor Plant Food, All-Purpose Indoor Plant Fertilizer, Liquid Plant Food, Easy Peasy Plants House Plant Fertilizers 4-3-4 Plant Nutrients, House Plant Food | Lasts Same as 16 oz Bottle | Organic Liquid 4-2-4 | Lasts up to 3 weeks High concentrate reduces plastic bottle use by 50% Specific ratio of NPK for indoor plants with added sulphur promoting better nutrient uptake |
My personal favourite best fertilizer for indoor plants is Espoma Plant-Tone because it is an organic fertilizer that can simply be mixed into the soil. The packaging is resealable and can easily be stored in your cupboard. No messing around with watering cans and measuring cups, what could be more easy?
When to fertilize indoor plants?
For outdoor plants the seasons influence their growth. In spring, when there is an increase in light and temperature, a plant responds by growing and preparing to grow fruit or flowers. In winter, when there is a decrease in light and temperature, a plant responds by becoming inactive or dormant, some even shedding their leaves.
In contrast, indoor plants may not experience the same changes in light and temperature. Their indoor environment is generally more stable with artificial and controlled lighting and temperature. However, most indoor plants still have a period of dormancy in autumn and winter and a period of increased growth in spring and summer. Strangely, they still sense seasonal changes in light and temperature even though they are indoors and less exposed to changes in light and temperature.
Therefore, it is not always easy to know when the best time may be to fertilize indoor plants but there are some common tips and tricks:
- Don’t fertilize your indoor plant immediately after purchase. Most garden centers regularly fertilize their plants and it is unlikely to need fertilizing straight away.
- Don’t add fertilizer to potting mixes unless the fertilizer product is formulated for this. Most potting mixes have fertilizer included and adding more could burn the roots of your plants.
- Don’t fertilize your indoor plants in winter or during (semi) dormant periods. Fertilizing at this time can result in poor growth and leave them susceptible to bugs and diseases.
- If your indoor plant is still actively growing throughout the cooler months, continue to fertilize your plant but reduce the amount of fertilizer and the frequency (by at least half).
- If your indoor plant is actively blooming throughout the cooler months, continue to fertilize as normal to support its growth and health.
- After winter, normally around February (in the northern hemisphere) and around August (in the southern hemisphere) begin fertilizing your indoor plant. This will help it prepare to grow foliage, flowers and fruit.
- If your indoor plant is not doing well, do not over fertilize as this can kill the plant. Instead, check that it has adequate light and water (perhaps check its label for guidance) and that its soil is not contaminated (e.g. signs of over fertilization, ants in the soil, poor quality soil).
How do I use fertilizers and how often should I fertilize my indoor plants?
The questions of how to and how often to fertilize indoor plants are two of the most common questions. These questions are actually quite easy to answer. But the simplest advice is to always follow the instructions on the fertilizer labels. Each fertilizer is different. To start you should follow both the frequency of application and amount to apply from the directions. Then you can make adjustments as needed.
Generally, liquid fertilizers are added to water and applied at regular intervals (sometimes every time you water, sometimes at every other time you water). It is important to follow the directions on the amount of fertilizer to water. Some are pre-mixed in the recommended ratios making it even easier for the indoor gardener. Some liquid fertilizers are meant to be applied directly to the roots. In this case, avoid the leaves and apply to the soil so the fertilizer gets straight to the roots. Other liquid fertilizers recommend being applied directly to the leaves. In this case, use a spray bottle and saturate the leaves well.
Granular fertilizers should be used as often as, and in the method described in the fertilizer directions. Remember that granular fertilizers release nutrients into the soil quickly when the plant is watered, so more frequent feedings than other types of fertilizers may be required. Granular fertilizers can be mixed into the soil when repotting, but check that your potting mix and the fertilizer instructions support this.
Slow-release fertilizers should also be applied according to the instructions. Be careful because these fertilizers can last up to two months or more. Don’t assume that because the stick or pod is no longer visible that you need to add more fertilizer. Slow-release fertilizers are inserted directly into the soil, generally away from the stem of the plant. The fertilizer can be more concentrated immediately next to the stick or pod. It is possible for slow-release fertilizers to be releasing nutrients but not necessarily in the areas where there are roots. So spread your spikes or pods around the pot evenly, especially if you are treating a large indoor plant.
What happens if I over fertilize?
We all want our indoor plants to thrive and grow beautiful foliage, flowers and fruit. We want to provide the best plant food for indoor plants. But too often this love turns into a common mistake made by many indoor gardeners – too much fertilizer.
If too much fertilizer is applied, regardless of the type of fertilizer, the water in the soil becomes ‘salty’ and burns your plant’s roots.
If you see a whitish crust on the surface of the soil or around the rim of the pot, these are both signs of over fertilization.
If you suspect over fertilization or a build up of salts in the soil, you can drench your indoor plant.
Preventing over fertilization
Fertilizers can build up in the soil. The best way to prevent this, is to essentially wash any remaining fertilizer from your pots two or three times per year. This is done by drenching your pots with a lot of water, allowing the water to flow gently through the pot. Then let the pot drain completely.
Diagnosing sick indoor plants
Trying to work out what is wrong with your indoor plant? The following table of symptoms that may help you diagnose which nutrient your plant is craving.
| Potential Cause | Symptoms |
| Lack of nitrogen | Old growth leaves that are yellowing. Foliage that unnaturally lighter in colour when it is supposed to be dark green. |
| Lack of phosphorous | Plants do not produce flowers or have dropped flowers. Leaves are unnaturally purple or reddish in color. Old foliage that is abnormally dark green. Leaves that have a burnt appearance at the tip. |
| Lack of potassium | Wilted old growth. Leaves that look scorched or blackened in appearance. |
| Lack of magnesium | Old growth leaves with yellow edges. |
| Lack of calcium | New leaves that are misshapen or warped. |
| Too much fertilizer | Whitish crust on the surface of the soil or around the rim of the pot |
Again, be gentle. A rapid change in the level of nutrients may shock or burn your plant.
Conclusion
So, you now know how to provide your indoor garden with just the right amount of tender love and care to ensure that your indoor plants have everything they need to grow beautiful flowers, lush green foliage, strong roots and fight disease. Finding the best fertilizer for indoor plants can be tricky but with a little knowledge you will be able to pick the right type and feeding schedule for your plants.
Slow-release fertilizers are very low maintenance with most able to provide nutrients to your plants for many months. Liquid fertilizers offer more control over the amount of nutrients your plants are getting but require a little more time investment. Granular fertilizers are great if you don’t want any hassle.
Keep a look out for resealable packages, smaller quantities and containers that can be easily stored in the home environment. And remember, to keep these out of reach of children and animals.
My personal favorite is Espoma Plant-Tone because it is an organic fertilizer that you simply to mix into the soil. There is low risk of over fertilization because it is organic and no messy mixing.
Don’t forget to get to know your plants and their needs. A little time invested in reading about your plants can be fun, relaxing and bring great results. Your plants will return your love and care by contributing to the health and wellbeing of your indoor space and providing oxygen.
Remember, life is better with indoor plants!
