Houseplant Fertilizers: A Beginner’s Guide

Caught up in acronyms like NPK, distinctions between organic and synthetic, and a range of seemingly complex phrases to decipher? With all the information available, houseplant fertilizing can seem like a technical and complicated care task.

However, once you understand the basics of feeding and the needs of your plants, it is no more difficult to manage than any other garden chore.

Let’s dive into the basics of houseplant fertilization, simplifying the process to ensure your indoor garden thrives.

Plant Nutrients Explained

There are a few essential resources plants need to survive – light, water, and nutrients. Light and water are easier to understand and track, but nutrients can seem more complex.

Plant nutrients are in three basic categories: macronutrients, secondary nutrients, and micronutrients. You’ll recognize the macronutrients as NPK on fertilizer packaging (nitrogen, phosphorus, potassium), but secondary nutrients like calcium and micronutrients like iron are also essential to monitor.

All these nutrients play vital roles in plant growth, but each is needed in slightly different amounts. In other words, a macronutrient like nitrogen is no more important than a micronutrient like iron; plants just need more nitrogen than iron to grow successfully.

Nutrients are found in the soil and are transported to parts of the plant that need it as moisture is drawn up through the roots. As nutrients are absorbed, the soil is replenished outdoors by decaying plant debris and other activity.

However, houseplants are confined in containers indoors, with a finite amount of soil to work with.  That means the available nutrients are slowly used up over time or leach from the soil as water escapes from the drainage holes. Eventually, too few nutrients will be left to keep the plant alive, requiring action from you in the form of fertilizing.

Types Of Fertilizers

When searching for fertilizers for your houseplant, several different types are available.

Liquid fertilizers are the most commonly used on houseplants. They are typically diluted in water and poured over the soil as part of your regular watering schedule. These nutrients are immediately available, requiring regular top-ups.

You can sprinkle granular fertilizers on top of the soil or mix them in when repotting. This will release nutrients over time as you water. They typically last longer than liquid fertilizers, especially with larger pellets, although there is a greater risk of overfertilizing if you don’t follow the instructions closely.

Fertilizers can also be organic or synthetic. Organic fertilizers derived from plants or animals, such as seaweed-based fertilizers, add nutrients to the soil over time as the organic molecules break down. Unlike many organic fertilizers, synthetic fertilizers contain a certain amount of nutrients and deliver quicker results but don’t contribute to soil health.

Do All Houseplants Need Fertilizer?

If you’re a hands-off plant parent, you may be wondering how important fertilizing is for each of your houseplants. But if you want to keep your plants alive long-term, it’s not something you should skip.

When you first purchase your plants, you probably won’t need to fertilize for a while. Growers typically mix fertilizer into the houseplant soil, maintaining nutrient levels for a while. However, the plant will eventually use those nutrients up, and that’s where fertilizer comes in.

Houseplants don’t need much fertilizer, typically growing slower indoors than outdoors. But all houseplants will benefit from feeding at some point, especially if you haven’t replaced the soil in a while.

There are a few factors that influence how much fertilizer your houseplants need. Species is the first factor, as some plants are heavier feeders than others. The environment also plays a role in determining how quickly the plant grows and, by extension, how quickly the nutrients are used up. The quality of the soil and time between repotting will have an influence, too.

Regardless of the amount, you should fertilize all your houseplants at some point during the growing season, including your succulent houseplants.

What Fertilizer Is Best For Houseplants?

The ideal fertilizer for your houseplants may change depending on the types of plants that you have.

Most common houseplants are leafy and tropical. To completely replenish the soil and provide all the nutrients needed, I like to use a balanced fertilizer with relatively equal parts nitrogen, phosphorus, and potassium. Good fertilizers should also contain some secondary and micronutrients for all-around plant health.

Balanced fertilizers are also useful for most succulent plants. Alternatively, you can look for a fertilizer slightly lower in nitrogen to prevent leggy growth, keeping your geometric succulents compact.

A nutrient imbalance may be to blame if you have any flowering houseplants struggling to flower. In that case, choose a fertilizer slightly higher in phosphorus to promote flowering at the right time.

Ultimately, it’s best to research the nutrients your houseplants need most to choose the best fertilizer for that time of year.

When To Feed Houseplants

Houseplant growth changes throughout the year based on the seasons and environment. It stands to reason that your feeding schedule should change, too, based on these adjustments.

Most houseplants don’t go completely ‘dormant’ during the cooler months, as some people claim. However, slight drops in temperature and fewer hours of sunlight during the day lead to slower growth than in the spring and summer months, using up less nutrients.

I follow this general schedule throughout the seasons, with some adjustments depending on the specific plants. Monitoring plant growth and soil health is essential to ensure you feed at the right time without overdoing it.

Spring and Summer

Apply your first round of fertilizer a few weeks before spring begins (or a few weeks before your last frost if you live in a colder climate). This will boost nutrients in the soil as growth increases, assisting new leaf and stem development.

Continue feeding your houseplants throughout the warmer months, slowing down if you notice any signs of overfertilization. Liquid fertilizers are usually applied every few weeks, while granular fertilizers are applied around once a month. Slow-release fertilizers last even longer and are generally only needed once per season.

Make sure you follow the instructions on the packaging. Different products have different concentrations and may need to be diluted before application. They will also generally guide you on how often to feed your plants.

To stay safe, I prefer to apply houseplant fertilizers at half strength. You can always apply more if needed, but it takes much longer for your plants to recover from accidentally overfeeding than underfeeding. Half-strength fertilizers applied at regular intervals should provide enough nutrients for your houseplants to thrive.

Fall and Winter

During the cooler months, your houseplants will not grow as vigorously as during spring and summer. Adjusting your fertilizing schedule will prevent accidental overfertilizing that may stunt growth the following season.

Most houseplants will benefit from a complete fertilizer break in fall and winter. You can continue feeding in the fall if you feel your plants need a few extra nutrients, simply fertilizing less often than you would during the warmer months. Avoid feeding at all in winter when little new growth emerges.

If you live in a much warmer climate with plenty of light year-round, your houseplants may grow well into fall and winter. In that case, you can continue feeding in limited amounts, increasing as spring approaches.

How To Feed Houseplants

Before you start feeding, make sure your houseplants are well-watered. If you fertilize when the soil is dry and the plants are stressed, you risk burning the roots if you use synthetic fertilizer (although organics don’t typically cause nutrient burn). If you’re using a liquid fertilizer diluted in water, you don’t need to worry about watering beforehand to avoid overwatering.

The application method will depend on your chosen product. Liquid fertilizers are poured evenly over the soil or absorbed through the drainage holes by submerging the pot in the diluted fertilizer solution.

Granular fertilizers are usually sprinkled over the top of the soil and gently worked in. Whenever you water, nutrients will be released and absorbed through the roots. You can also purchase houseplant fertilizer sticks you may stick into the soil to break down slowly over time.

Avoid getting any fertilizer on the leaves or stems whenever you’re feeding, as this wastes the fertilizer and may cause leaf scorch. Focus on the soil only, where nutrients are most useful. Also, ensure you empty any pot covers or drip trays after feeding if you have used liquid fertilizer.

Remember that fertilizers won’t be useful if the soil in the container is poor quality. If you continuously have to feed your houseplants and they still show signs of struggle, it’s probably time to repot.

Signs of Overfertilization

When you notice these issues just after fertilization, flush the soil with water until it runs clear. This will remove as much of the excess synthetic fertilizer as possible. Hold off on fertilizing for a while to give your plant time to recover.

If flushing the soil doesn’t solve the problem, you can try repotting into fresh soil. This will allow you to trim the damaged roots, leaving space for new and healthy growth.

In both cases, this should not be an issue with organic fertilizers. It’s extremely hard to cause nutrient scorch to plants with an organic product! However, it’s not entirely impossible, so err on the side of caution.

Signs of Underfertilization

When you’re ready to fertilize, don’t overcompensate by applying more fertilizer than needed. Follow the instructions and adjust your routine to avoid problems with overfertilizing in the future.

Final Thoughts

Fertilizing is a vital part of houseplant care. Follow these steps to give your houseplants exactly what they need at the perfect time.