The number of fertilizers for indoor plants can seem overwhelming, but shopping is easier if you know a few basic facts. First, fertilizers provide different amounts of essential macronutrients to your plants: nitrogen, phosphorus, and potassium (these are listed as N-P-K ratios on the packaging). Some fertilizers also provide plants with varying amounts of micronutrients and microbes to help the plant take up more of the valuable nutrients in the plant food. Fertilizers are available as liquid, granule, or slow-release formulas—each type has advantages and disadvantages. “Indoor plants use nutrients from the soil during periods of active growth (typically from spring through fall),” says Jessica Walliser, horticulturist, author, and co-founder of SavvyGardening.com. “Because Indoor plants are growing in the restricted environment of a container of potting soil, it’s important for us to provide them with nutrients.” The best fertilizers for indoor plants provide a balanced amount of macronutrients to your indoor plants. Because it’s easy to over-fertilize houseplants, it’s important to follow the instructions on the packaging carefully and err on the side of caution. “Choose fertilizers with low NPK numbers, opt for organic options whenever possible, and don’t forget that many potting soils have fertilizer already in them,” Walliser says. Our top pick for the best fertilizer for indoor plants is Espoma Organic Indoor Houseplant Food. It’s easy to apply since the cap doubles as a measuring tool, and because it’s a liquid, you’re less likely to accidentally give your plants too much fertilizer. Here’s our full list of the 11 best fertilizers for indoor plants. Keep in Mind: It may not have a high enough amount of phosphorus for flowering houseplants. The fertilizer’s blend of 2% nitrogen, 2% phosphorus, and 2% potassium works well for most houseplants, so there’s no need to have multiple types of fertilizers on hand for various plants. Plus, because it’s less potent than some, there’s less risk of overdoing it. Beneficial microbes in the product help the plant take up all the nutrients that are included in the fertilizer. For best results, you’ll need to reapply every two to four weeks. This is not as often as some other types of fertilizers, but it does require a bit more work than the long-lasting slow-release fertilizers you only need to apply every few months. We also like that, because the Espoma Organic Indoor Houseplant food uses non-toxic ingredients, it’s safer to use around people and pets. However, if you have flowering plants, you may want to get a fertilizer with a higher concentration of phosphorus. Price at time of publish: $28 Type: Liquid | Nutrient Levels: 2-2-2 | Organic or Synthetic: Organic | Suggested Frequency of Use: Every two to four weeks | Quantity: 8 ounces Keep in Mind: It’s not made with organic ingredients, so it’s not suitable for organic gardeners. To use this fertilizer on houseplants, simply mix half a teaspoon of the liquid fertilizer with a gallon of water in a watering can and soak the base of your plants. You should plan to apply every one to two weeks during the growing season. Be sure to follow the instructions carefully to avoid applying too much and burning your plants. For outdoor plants, you can use more of the fertilizer: 1 tablespoon of fertilizer per gallon of water. This formula is relatively potent, providing 24% nitrogen, 8% phosphorus, and 16% potassium. This is a good amount more than a number of other fertilizers designed for houseplants. The high concentration of nitrogen can help foliage plants grow, and the phosphorus will give flowering plants a boost, too. It’s important to note that the Miracle-Gro Water-Soluble All-Purpose Plant Food is made with synthetic ingredients rather than organic ones. This means they will eventually deplete the soil’s quality. People who prefer to use organic fertilizers for indoor plants will want to avoid this option. Price at time of publish: $6 Type: Liquid | Nutrient Levels: 24-8-16 | Organic or Synthetic: Synthetic | Suggested Frequency of Use: Every one to two weeks | Quantity: .56 pounds Keep in Mind: It has a strong seaweed smell that shoppers may not like. Bloom City’s fertilizer is made with a blend of seven species of organic seaweed and kelp. It’s processed in order to extract the fibrous pulp that can create a brackish appearance. To apply it to your indoor plants, mix 5 to 10 milliliters per gallon of water in your watering can and pour the solution over the soil. You can also spray it on the leaves if you are applying it to a lot of plants or in a large area. It’s a good multipurpose formula; in addition to houseplants, you can use the fertilizer outside on vegetables, herbs, fruiting trees, and lawns. You can apply this to houseplants every time you water or once to twice a month if spraying outside. Because the fertilizer is made of seaweed, it has a strong, unpleasant smell that might bother you, especially if used in large quantities. Some shoppers noted that this formula smells better than most, and all fertilizer has the potential to leave behind a lingering odor, so this may not be a deterrent to most shoppers. Price at time of publish: $17 Type: Liquid | Nutrient Levels: Not listed | Organic or Synthetic: Organic | Suggested Frequency of Use: Use at every watering | Quantity: 32 ounces Keep in Mind: It can be easy to overfeed your plants with this type of fertilizer, so be sure to follow the instructions carefully and err on the side of caution. After you insert the spike, the nutrients are gradually released into the soil over time without you needing to do anything more. Plus, the nutrients are released near the roots—right where the plants need them most. The directions on the packaging tell you how many spikes are needed based on the diameter of your pot, which will help prevent you from accidentally overfeeding your plant. These fertilizer spikes provide 13% nitrogen, 4% phosphorus, and 5% potassium. The high nitrogen level should help increase foliage growth substantially. Although this product doesn’t have as much phosphorus as some fertilizers, it should work well for flowering houseplants too. Keep in mind that over-feeding your plants with this type of fertilizer will cause them to wilt, turn brown, and lose their leaves. Make sure not to add a new spike to your soil for at least 60 days to avoid over-fertilizing your houseplants. It’s also important to note that these spikes are designed for houseplants, not vegetables or outdoor plants. Price at time of publish: $7 Type: Granule (spikes) | Nutrient Levels: 13-4-5 | Organic or Synthetic: Synthetic | Suggested Frequency of Use: Every 60 days | Quantity: .01 ounces/30 spikes Keep in Mind: Since it’s a granule product designed for both indoor and outdoor plants, it’s very easy to over-apply. For new container plantings, add 2 tablespoons of fertilizer per gallon of soil and water well. After three or four weeks, you can apply the fertilizer as a top dressing by scratching it into the top inch of soil and following the application guidelines based on your plant’s height. These instructions are intended for both indoor and outdoor plants, so indoor plants with less soil may not need as much. As with any fertilizer, it’s important to follow the instructions carefully. Granule fertilizers can be easy to over-apply by accident, so we recommend using a little less than the recommended dosage for your indoor plants to avoid giving them too much. Price at time of publish: $19 Type: Granule | Nutrient Levels: 6-4-5 | Organic or Synthetic: Organic | Suggested Frequency of Use: Once a month | Quantity: 64 ounces Keep in Mind: Depending on how many indoor plants you have, one bottle may not last very long. Thanks to the innovative pump top, which makes it super easy to dispense the perfect amount of product, you can add the liquid fertilizer directly to the soil in your houseplant’s container. The manufacturer recommends one pump for small pots and two pumps for large pots. Or, if you prefer to apply this liquid fertilizer in a diluted form, you can mix four pumps with a quart of water and apply to your plants with a watering can. You will need to reapply once a week, which admittedly is more often than many other types of fertilizers. However, it’s so easy to use that we don’t mind applying it often. Depending on how many indoor plants you have, you can choose to buy a single bottle, this two-pack, or stock up with a six-pack of fertilizers. Price at time of publish: $11 Type: Liquid | Nutrient Levels: 1-1-1 | Organic or Synthetic: Synthetic | Suggested Frequency of Use: Once per week | Quantity: 8 ounces Keep in Mind: It’s made of synthetic ingredients rather than organic. Osmocote’s Smart-Release Plant Food keeps working for up to four months after you apply it. Although that may sound unbelievable, it works because each granule of the fertilizer is coated with a resin that controls how quickly the nutrients are released into the soil. And since the nutrients in Osmocote’s fertilizer are released based on changes in temperature, the plant will receive more nutrients during the growing season (when they need them most). This fertilizer contains 15% nitrogen, 9% phosphorus, and 12% potassium, and it works for many different plant varieties and growing conditions. It also comes with the company’s no-burn pledge, which promises that your plants won’t get burned when you apply it at the recommended rate. Keep in mind that it is a synthetic product and not suitable for organic gardening. To apply, sprinkle one scoop of fertilizer for every 2 gallons or 4 square feet of soil, mix it into the top 1 to 3 inches of soil, and then water as you normally would. The directions include appropriate amounts for different sizes of pots: for example, 1 teaspoon is recommended for an 8-inch pot. Price at time of publish: $10 Type: Slow-release granules | Nutrient Levels: 15-9-12 | Organic or Synthetic: Synthetic | Suggested Frequency of Use: Every four months | Quantity: 1 pound Keep in Mind: It’s easy to overfeed with granule fertilizers, so follow the instructions carefully. For houseplants and container-grown plants, simply mix two heaping tablespoons of the fertilizer per gallon of soil (which is roughly equal to the soil in a 4-inch pot). You can mix this granular fertilizer in with the potting soil during planting or gently work the fertilizer into the top inch of soil for established plants. This fertilizer provides a balanced mix of nutrients, which is what makes it so suitable for a wide array of plants. It contains 4% nitrogen, 6% phosphorus, and 5% potassium. It’s made from fish bone meal, alfalfa meal, fish meal, potassium sulfate, and kelp meal. Use it once a month for houseplants and about once every eight weeks for flowers, trees, and shrubs. Keep in mind that granulated fertilizer can be very easy to over-apply, so be extra cautious not to feed your potted plants too much or too often. Follow the instructions closely to avoid damaging your indoor plants. Price at time of publish: $14 Type: Granule | Nutrient Levels: 4-6-5 | Organic or Synthetic: Organic | Suggested Frequency of Use: Once per month | Quantity: 64 ounces Keep in Mind: You’ll need to use up to eight pods at a time for large plants, so you may run out of fertilizer more quickly than others. The Earth Pods will break down over time and slowly release nutrients directly into the soil near the root zone. You’ll need to reapply them every two to three weeks. These capsules can be used on flowering bulbs, houseplants, annual flowers, and flowering shrubs. For small plants, you’ll only need one or two EarthPods, but you may need up to eight for large plants. To give your cut flowers an added boost, simply dissolve one or two capsules in a vase of lukewarm water and place the stems directly inside. While many easy-to-use spikes, pellets, and fertilizer capsules contain synthetic ingredients, we like that the EarthPods Organic Flower Food Fertilizer spikes are made with organic ingredients. The packaging is even made from recycled paperboard printed with soy ink, minimizing this product’s long-term impact on the environment. It’s important to note that the manufacturer doesn’t disclose the exact nutrient breakdown in its fertilizer capsules, so you won’t be able to compare it to other products based on its N-P-K contents. Be sure to follow the instructions carefully to ensure you don’t accidentally over-feed your plants. Price at time of publish: $38 Type: Capsules | Nutrient Levels: Not Listed | Organic or Synthetic: Organic | Suggested Frequency of Use: Every two to three weeks | Quantity: 4 ounces/100 capsules Keep in Mind: It has a strong lingering smell after applying. In general, herbs don’t require a ton of fertilizer, so this granular fertilizer contains 2% nitrogen, 5% phosphorus, and 3% potassium to give them an all-around boost. The phosphorus in particular helps it produce more greenery, resulting in more herbs for you to harvest and enjoy. Additionally, the fertilizer also contains a proprietary blend of healthy bacteria and mycorrhizal fungi that help break down nutrients into the soil and improve the soil quality over time. The product instructions recommend that you apply this fertilizer every four to six weeks. Because it’s a granular fertilizer, it can be easy to apply too much fertilizer, so follow the directions carefully. Like most fertilizers, Jobe’s Organic Granular Plant Food has a strong smell. However, many users reported that the scent lingers for a long time, so we recommend applying the fertilizer in a well-ventilated area for best results. Price at time of publish: $9 Type: Granule | Nutrient Levels: 2-5-3 | Organic or Synthetic: Organic | Suggested Frequency of Use: Every four to six weeks | Quantity: 4 pounds Keep in Mind: It can be difficult to apply without spilling. We like that this is a liquid fertilizer, which is easier to apply correctly than a granular fertilizer. You can apply this product every two weeks during the growing season—just mix 1 teaspoon with one gallon of water and apply to the base of the plant with a watering can. We wish the bottle had a pouring spout, as it can be a little difficult to apply this fertilizer evenly without spilling. Be extra careful when pouring it to avoid getting it on yourself or on nearby surfaces. Price at time of publish: $15 Type: Liquid | Nutrient Levels: 1-7-6 | Organic or Synthetic: Synthetic | Suggested Frequency of Use: Every two weeks | Quantity: 16 ounces
What to Know About Fertilizers for Indoor Plants Before Shopping
Fertilizer Type
The best fertilizers for indoor plants are available in three main forms: liquid, granular, and slow-release. Liquid fertilizers are diluted with water and applied through a watering can. No matter what form you choose, we recommend shopping for organic fertilizers over those with synthetic ingredients. “Organic liquid fertilizers are my first choice for indoor plants because it’s easy to control the amount and frequency of their application,” Walliser says. “Plus, liquid fertilizers are available for plant use very quickly.” Granule fertilizers are sprinkled on top of the soil and then mixed into the soil with water. This type of fertilizer is often less expensive than liquid or slow-release options, but it can be easy to apply too much fertilizer if you don’t follow the instructions carefully. Slow-release fertilizers inject nutrients into the potting soil over an extended period of time. They may cost more than other types of fertilizer, but one application will last for several months, so you won’t need to re-apply as often. Many are made from synthetic rather than organic ingredients and they are available in several forms, such as pellets, spikes, pods, and capsules.
Nutrient Levels
As a general rule, the best fertilizers for indoor plants will provide a balanced level of nitrogen, phosphorus, and potassium, but keep in mind that not all houseplants will need the same nutrients. Flowering plants will benefit from a fertilizer that’s high in phosphorus, which supports blooms, while young houseplants will do well with a fertilizer high in nitrogen that encourages healthy growth.
Organic or Synthetic
Traditional synthetic fertilizers may be a little more fast-acting than an organic one, but organic fertilizers are made with all-natural ingredients that’ll have better long-term effects. To ensure that an organic fertilizer is safe for your organic garden, it’s a good idea to ensure it is OMRI-listed, which means it is approved by the Organic Materials Review Institute.
Suggested Frequency of Use
Always follow the manufacturer’s instructions when applying fertilizer to your plants, as this is the best way to ensure you don’t over-apply it. The best fertilizer for indoor plants will not help your houseplants if you put on too much. Depending on the type you choose, you may have to add new fertilizer every time you water your plant, or you might be able to wait several months in between. Keep in mind that houseplants need more fertilizer during the growing season and may have different needs during the winter months.
Quantity
When shopping for the best fertilizers for indoor plants, be sure to check not only the size of the package but how much fertilizer you will need to apply every time. Package size varies greatly between products, and some fertilizer packages may not go as far as you think—especially if you have a lot of houseplants.
Your Questions, Answered
Can you make homemade fertilizer?
It is possible to make your own fertilizer, but keep in mind that homemade fertilizer isn’t necessarily better than store-bought options, Walliser says. Repurposing leftovers from your favorite fruits may be harmful and coffee grounds are a better bet for your compost pile than your houseplant collection. Mixing ingredients can be a tricky proposition, too. You may not end up with the desired ratio of nitrogen, phosphorus, and potassium, which can result in too much of one nutrient to your plants and not enough of another. Often the best fertilizer for indoor plants is one you buy, but if you want to go the homemade route, Walliser recommends making worm casting tea from your vermicomposting bin, or just scooping a small trowel of worm castings into your potting soil two or three times a year. (Note: You can purchase worm castings if you don’t have a vermicomposting bin.)
How often do your plants need fertilizer?
Unfortunately, there isn’t a simple answer to this question. How often your plants need fertilizer will depend on a number of factors, including what type of fertilizer you use, the time of year, and the needs of your specific plants. Depending on your climate, houseplants may not need much fertilizer in winter. “If I’m using a liquid product, I fertilize my houseplants about once every four to six weeks from March through September while the plants are in an active state of growth,” Walliser says. “If you’re using organic granular products or synthetic slow-release fertilizers, only apply once or twice from March to September.”
Who We Are
Renee Freemon Mulvihill is a freelance writer who specializes in home and garden topics. To write this roundup of the best fertilizers for indoor plants, she researched products online and spoke with Jessica Walliser, a horticulturist, author of Container Gardening Complete, and co-founder of SavvyGardening.com.
