Houseplant Fertilizers: The Best Indoor Plant Fertilizers (Reviewed and Compared)
Houseplant fertilizers help feed indoor plants with all the nutrients they need to thrive. The best indoor plant fertilizers should contain a balance of minerals to ensure plants have healthy roots, lush foliage, and beautiful flowers. Fertilizers for houseplants can be like liquid plant food, nutrient-rich granules, or slow-releasing pods.
Choosing the best type of houseplant fertilizer can be tricky. Although there are types of all-purpose liquid plant food, some houseplants have specific nutrient requirements. So, you need to choose one that contains the right balance of micro- and macro-nutrients that individual house plants need.
This article contains a complete guide to houseplant fertilizers. You will learn about the various types of organic and liquid plant fertilizers. Also, a detailed review of the top indoor plant fertilizers will help you choose which is the best one for your potted plants.
Why Indoor Plants Need Fertilizer
Houseplants need fertilizing to provide nutrients for healthy growth. Regular feeding replenishes the potting soil with minerals that indoor plants require. It’s vital to fertilize indoor plants because—unlike outdoor plants—they have no supply of organic matter. Applying fertilizer at regular times ensures your houseplants continue to grow healthy.
Scientifically speaking, fertilizer is different from plant food. Most plants generate their own food by absorbing water and carbon dioxide. However, plants also need other nutrients that are found in the soil such as nitrogen, phosphorous and potassium. Fertilizers provide these nutrients to the plants.
Plants get their food during photosynthesis when they get energy from light. Plants absorb carbon dioxide from the air and water from the soil. These combine to produce sugars that the plant uses for food. So, plants feed themselves by making their own food.
Of course, plants need more than food to thrive. Fertilizing plants regularly ensures they get essential macro-nutrients—nitrogen, phosphorus, and potassium—that are usually lacking in potting soil. Even though plant food technically isn’t a fertilizer, most people use the term interchangeably.
When Should You Fertilize Houseplants?
Fertilize your houseplants when they are actively growing during the spring and summer. The frequency of applying fertilizer depends on the type of houseplant. Some houseplants are heavy feeders and require fertilization as often as every week. Other slow-growing houseplants may need feeding monthly, or even less frequently.
Types of Houseplant Fertilizers
There are generally three types of fertilizers for indoor plants: Liquid houseplant fertilizers are added to water that you apply when needed when watering plants. Granular plant fertilizers are mixed into the soil, and they release nutrients when plants get water. Slow-release fertilizers gradually release nutrients into the soil.
Many houseplant owners choose types of organic houseplant fertilizers rather than synthetic ones. Organic indoor plant fertilizers help improve the quality of soil and “feed” plants with essential nutrients. Usually, kelp, fish emulsion, worm tea, compost tea, or plant extracts are ingredients in the most popular organic fertilizers.
The Best Fertilizers for Indoor Plants
What is the Best Type of Fertilizer for Indoor Plants?
Choosing the best type of houseplant fertilizer depends on several factors. Apart from getting the mineral balance right for your plants and the soil type, you have to decide on the kind of fertilization method. Each method of fertilizing plants has its advantages and disadvantages.
What kind of fertilizer is best for your houseplants? Here are a few things to consider when choosing between the different types of indoor plant fertilizers:
Liquid fertilizers—Liquid plant food is easy to apply and control. You just have to dilute to the appropriate strength and fertilize your plants when they need feeding. Choosing liquid fertilizers means you can hold off fertilization during the dormant winter months.
A disadvantage of liquid fertilizers is having to remember to fertilize. Also, it can be tricky to get the quantities just right. If you only have a few houseplants to feed, you can end up throwing fertilizer away because a teaspoon can make a gallon of liquid plant food.
Slow-release fertilizers—Pods, spikes and capsules slowly release nutrients into the potting soil. The advantage of these is that you don’t have to remember to feed plants. However, it’s difficult to control how much nutrients get into the potting mix. Slow-release plant fertilizers are more suitable for small pots.
Granular fertilizers—This type of fertilizer is best when repotting a plant in fresh soil. The granules are worked into the soil, and they release nutrients when you water the plant. Similar to slow-release fertilizers, it’s difficult to control the strength of fertilization.
Organic houseplant fertilizers—Organic fertilizers can be liquid, granular, or slow-release fertilizers. The advantage of organic liquid plant food is that it is environmentally friendly and improves the soil structure. Also, there is less risk of root burn and excess mineral in the soil when using organic fertilizers for houseplants.
What’s in Houseplant Fertilizer?
Fertilizers for indoor plants contain a combination of micro- and macro-nutrients. The three essential minerals are nitrogen (N), phosphorous (P), and potassium (K). The best houseplant fertilizers also contain other nutrients such as calcium, iron, magnesium, zinc, and boron.
On plant fertilizers, the nutrient balance is written as N-P-K, or it could be a series of three numbers.
The Best Type of Fertilizer for Indoor Plants
The best kind of indoor plant fertilizer depends on the type of plants you grow. Generally, flowering plants need a higher ratio of phosphorus. In contrast, non-flowering indoor plants need more nitrogen for healthy growth. For most indoor plants, a balanced plant fertilizer is ideal.
For example, 7-9-5 NPK is ideal for small potted flowering plants such as African violets or begonias. However, other types of flowering houseplants need a 1-3-1 combination. Green, leafy tropical indoor plants need a higher nitrogen ratio. Or a balanced indoor plant fertilizer is ideal such as 5-5-3 or 5-5-5. One of the most common all-purpose liquid plant foods is a 20-20-20 fertilizer.
Commercial potting mixes are specially formulated for specific plant types. So, a soil medium for cacti and succulents would have a different ratio of nitrogen, phosphorus, and potassium than a potting medium for calatheas, hoyas, or peperomia. Also, flowering plants require a different type of fertilizer than plants that never flower indoors.
The Best Indoor Plants Fertilizer Reviews
Let’s look in more detail at some of the best indoor plant fertilizers. Here you’ll find some types of liquid plant “food,” fertilizer granules, organic indoor plant fertilizers, and slow-release fertilizer sticks.
1. Miracle-Gro Plant Food (Liquid), Feeds Indoor Houseplants
This liquid plant food is an all-purpose houseplant fertilizer by Miracle-Gro. The balanced fertilizer has an even N-P-K ratio of 1-1-1. The handy pump application means you can feed plants directly from the bottle. Or, you accurately measure fertilizer to dilute with water to hydrate all types of houseplants.
This all-purpose fertilizer is also suitable if you grow edible plants indoors. The manufacturer recommends feeding plants weekly with this plant food.
2. Espoma Company Organic Indoor Plant Food
This liquid organic houseplant fertilizer is easy to use and mix. The balanced, all-purpose plant feed has an N-P-K ratio of 2-2-2 and is suitable for any type of indoor plant. The liquid fertilizer is made from poultry manure, kelp extract, fish protein, and bone meal.
This houseplant liquid fertilizer has micro-nutrients added to help keep your plants healthy. Additionally, beneficial microbes keep soil healthy and fertile. The handy measuring cap helps reduce the risk of over-fertilizing houseplants.
3. Organic Liquid Seaweed and Kelp Fertilizer
Kelp and seaweed are excellent natural fertilizers that feed your plant with the essential three macro-nutrients. The kelp fertilizer by Bloom City contains natural enzymes to improve the health of plants. Because this is a natural product, there is no risk of over-fertilizing.
This kelp extract fertilizer contains seven species of sea plants. The seaweed extract strengthens roots and improves soil for vigorous plant growth. Unlike some cheap seaweed fertilizers, this product doesn’t contain fillers. It has a wide range of naturally occurring enzymes, sugars, and growth hormones that your indoor plants need.
4. Osmocote Smart-Release Plant Food Plus Outdoor & Indoor
This granular, slow-release plant fertilizer keeps your plants fed for up to six months. The formula has an N-P-K ratio of 20-20-20 and contains copper, boron, iron, manganese, and zinc. The granules are coated with resin to release nutrients gradually when you water the plant.
To use this granular houseplant fertilizer, work in the granules to the top 3-inch (7.5 cm) layer of potting soil. The manufacturers have a “no burn” guarantee if you use the fertilizer correctly.
5. Miracle-Gro Water Soluble Plant Food
This multi-purpose fertilizer is suitable for all types of houseplants and outdoor plants. The plant food is in granular form that you mix with water before feeding plants. The N-P-K ratio is 18-18-21, so it’s excellent for all kinds of plants. The manufacturers recommend feeding plants every one to two weeks.
As well as having the three crucial nutrients for plants, the plant food has traces of magnesium, copper, iron, and zinc. You only need one teaspoon of plant food for every gallon of water.
6. Miracle-Gro 1001502 Liquid All Purpose Plant Food
Another type of fertilizer is this liquid concentrate by Miracle-Gro. The formula has an N-P-K ratio of 12-4-8, which makes it excellent for houseplants and outdoor plants. A high level of nitrogen ensures rapid plant growth and lush green leaves. Follow the instructions to reduce the risk of root burn.
For best results, apply the liquid, all-purpose fertilizer two to four times a month. The balance of micro- and macro-nutrients will help replenish lost minerals in plant soil.
7. Jobe’s Indoor Plant Food Spikes
Fertilizer food spikes are an ideal way to keep your plants fed without remembering to apply plant food. These Jobe’s food spikes have an N-P-K rating of 13-4-5. The high nitrogen levels mean these fertilizer sticks are an excellent choice for indoor foliage plants.
To use plant food spikes, make a hole in the potting soil and insert the spikes. Cover with soil and water your plant as often as it needs—generally when the top layer of soil dries. Replace the spikes every month to ensure your plant gets enough nutrients to grow healthy.
8. SUPERthrive VI30148 Plant Vitamin Solution, 4 Ounce
This liquid houseplant fertilizer uses kelp to provide the essential vitamins and minerals that indoor plants need to thrive. The natural ingredients help to develop healthy soil and roots to promote healthy growth. The fertilizer is suitable for all indoor plants, as well as spraying on flowers and fertilizing lawns.
Unlike other types of houseplant fertilizers that rely on an NPK ratio, this is a vitamin growth supplement with high nitrogen levels.
9. Earthworm Technologies TeaDrops Organic Liquid Indoor Houseplant Food – All Purpose House Plant Fertilizer
TeaDrops produces an entirely natural liquid plant food that is suitable for all types of plants. An advantage of this liquid plant food is that there is no smell, measuring, or mess using the fertilizer tea bags. The nutrients, minerals, bacteria, and fungi encourage vigorous indoor plant growth.
This fertilizer has a low N-P-K rating because the ingredients stimulate the natural growth in plants.
To use TeaDrops fertilizer, you put one packet of fertilizer in a gallon (3.7 l) of water. Allow to steep for 24 hours and then use to feed your plants. The natural ingredients don’t cause root burn. TeaDrops also produces fertilizers for outdoor plants, as well as slow-releasing fertilizer capsules.
10. Jacks Classic All Purpose Fertilizer
This 20-20-20 fertilizer for indoor plants by Jacks has a balance of nitrogen, phosphorous, and potassium. The mineral balance makes this plant food ideal for foliage plants to ensure lush, healthy growth. Jacks fertilizer also contains micro-nutrients such as copper, iron, boron, zinc, and manganese.
To use this water-soluble houseplant fertilizer, mix the granules in water. Then apply directly to the soil to fertilize your plants every two weeks.
This all-purpose liquid plant food is also suitable for feeding marigolds, perennials, shrubs, vegetables, and lilies.
When to Fertilize Indoor Plants?
Fertilize indoor plants when they are actively growing during the spring and summer. Fertilize indoor plants at the start of spring, and continue until late summer—feeding the plants as often as necessary. Stop fertilizing plants that grow indoors during the fall and winter months. Plants are dormant during these months and you should hold off feeding them during this time.
The soil’s freshness also determines the right time to fertilize indoor plants. If you repot your plants in spring with fresh potting soil, you won’t need to feed plants for the next two months. Most modern potting soils are fortified with fertilizer for particular types of plants.
How Often Should You Fertilize Indoor Plants?
During the growing season—spring and summer—fertilize indoor plants regularly. How often you need to apply fertilizer depends on the plant’s growth rate. Some indoor plants grow vigorously and need fertilizing every two weeks. Indoor plants with a slow growth rate need feeding every three or four months.
Avoid fertilizing your houseplants too often. Applying a high concentration of fertilizer or feeding too frequently can cause a buildup of mineral salts. In time, plants can suffer from root burn and wilting growth. Flushing the soil is a way to rid the potting medium of excess fertilizer residue.
How to Fertilize Indoor Plants?
The way to fertilize indoor plants properly depends on the type of fertilizer you are using. In all cases, follow the manufacturer’s instructions and never over-fertilize. For example, many liquid fertilizers for indoor plants only need one teaspoon of liquid in a gallon (3.7 l) of water.
How to fertilize houseplants with liquid plant food
Here how is to use liquid fertilizer to feed indoor plants:
- Use the measuring cup or spoon and dilute the liquid fertilizer as per the manufacturer’s instructions.
- If the all-purpose liquid fertilizer is designed to be applied to the roots, ensure you pour the solution straight into the soil. It’s essential to avoid splashing the leaves.
- If the fertilizer is for leaf application, fill a spray bottle with the diluted solution and spray on the leaves.
How to fertilize indoor plants with granular fertilizer
To use granular fertilizer, this is what you should do:
- Mix in the granules into the top 3-inch (7.5 cm) layer of potting soil.
- Thoroughly water your houseplant to release the nutrients.
- Allow all the water to drain from the pot completely.
How to use slow-release fertilizer for indoor plants
Fertilizing houseplants with slow-release spikes, pods, or capsules is the easiest way to feed houseplants. This is what you should do:
- Create a hole in the soil or several holes if you have a large pot.
- Insert the slow-release houseplant fertilizer spikes directly in the soil.
- Choose a place about halfway between the plant’s stem and the edge of the pot.
- If you have a plant in a large pot, insert several fertilizer sticks to ensure an even distribution of fertilizer.
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