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An Essential Guide to Plant Fertilizer

Dec 1st, 2023

As indoor plant enthusiasts, we all want our leafy companions to thrive and bring a touch of greenery to our homes. While providing them with adequate sunlight and water is crucial, another essential factor that’s often overlooked is the use of fertilizer. Just like humans need a balanced diet to maintain good health, plants require a steady supply of nutrients to flourish — this is where plant fertilizers come into play.

How & why to use fertilizer on your plants

Why use plant fertilizer?

Soil loses its fertility over time, and the potting mix in our indoor planters gradually depletes of essential nutrients. Plants growing in these depleted conditions may exhibit signs of nutrient deficiency, such as stunted growth, pale or yellowing leaves and reduced flowering or fruiting. Fertilizers provide a replenishment of these essential nutrients, enabling plants to grow strong, healthy and vibrant.

emmaline (✿◠‿◠) on Instagram: "My current watering mix for my houseplants! I will typically make a batch and use it until empty and refill it. It’s super simple and produces beautiful plants! I laid out the benefits below! Rainwater: 🌿 does not contain salts, minerals, treatment chemicals like hard tap water. 🌿 contains macro-nutrients that are the most useful form of nitrogen that fosters the plant growth. 🌿 easy to access (in most areas) and store in containers for future use 🌿 eco-friendly and sustainable Fertilizer: 🪴 you can fertilize with every watering using only a half strength fertilizer solution. 🪴 continuously fertilizing gives the plant what it needs to thrive as houseplants leach nutrients every watering. 🪴 follow the label to avoid over-fertilizing, which can damage plants and send excess fertilizer into the environment. 🪴 I use miracle gro fertilizer but you can use any fertilizer you like. Hydrogen Peroxide: 🌱helps encourage healthy root growth because of the extra oxygen molecule. 🌱helps plant roots absorb nutrients from the soil which means faster, healthier, and more vigorous growth. 🌱helps discourage unwanted bacteria/fungi/pests that may be lurking in your soil - used HP for gnats and they are gone! ___ #houseplants #plants #rainwater #waterplants #wateringplants #fertilizer #plantfertilizer #plantpests #planttips #houseplanttips #houseplantcaretips #plantcare #plantcaretips #plantcareisselfcare #plantcareguide"

13K likes, 112 comments - plantwithemmaline on September 21, 2021: "My current watering mix for my houseplants! I will typically make a batch and use it until empty ..."

The main nutrients in plant fertilizers

Plants require a variety of nutrients for optimal growth, but the three most crucial ones are nitrogen (N), phosphorus (P) and potassium (K). These are often referred to as macro-nutrients, and their levels in fertilizers are typically indicated by a three-number ratio on the label. For example, a fertilizer labeled 10-20-30 contains 10% nitrogen, 20% phosphorus and 30% potassium.

Okay, so now we can translate the numbers, but what exactly does each nutrient do for the plant? Thankfully, it’s pretty easy to spot when a nutrient is lacking in your plant once you know what to look for. 

Nitrogen is essential for leaf growth and plays a vital role in photosynthesis. It also contributes to the overall green color of plants (it helps with the production of chlorophyll), so when there is not enough nitrogen, leaves start to turn yellow.

Phosphorus is crucial for root development, flower and fruit production and seed formation. Phosphorus is also important for energy storage and transfer, so when a plant is deficient in it, leaves can develop a purple or reddish hue.

Potassium regulates water and nutrient uptake, enhances disease resistance and promotes strong stems and roots. When a plant is deficient in potassium, leaf edges can turn brown and crispy.

While we’re at it, actually, here are just a few other more specific signs and symptoms you can watch out for in your plant. 

  • Interveinal chlorosis: A.K.A. “yellowing of the area between the leaf veins.” This is a common symptom of magnesium deficiency, which is important for chlorophyll production and enzyme function.
  • Pale green or yellow spots on leaves: This can be a sign of a deficiency in sulfur which is important for amino acid synthesis and protein production.
  • Holes in leaves: This can be a sign of boron deficiency, as long as you're sure that it’s not due to insects. Boron is important for cell wall development and nutrient transport — without enough of it, weak leaves can develop small holes or tears.
  • Twisted or misshapen leaves: Zinc is important for enzyme function and growth regulation, and when it is deficient, leaves can become twisted, misshapen or stunted.

Different types of fertilizers

Fertilizers can be broadly categorized into two main types: organic and inorganic.

Organic fertilizers are derived from natural nutrient-rich sources like animal manure, compost and plant matter. They release nutrients slowly over time, making them less likely to cause nutrient burn and are more environmentally friendly. You can even make your own natural plant fertilizers with food scraps!

Inorganic fertilizers are manufactured from synthetic chemicals. They provide a quick boost of nutrients, but excessive use can lead to leaching into waterways and environmental pollution. These are typically more readily available at gardening or hardware stores than the organic varieties. 

Determining what fertilizer to use

When choosing a fertilizer, there are a few factors to consider first:

Plant type: Different plants have varying nutrient requirements. For instance, flowering plants typically require more phosphorus, while foliage plants need more nitrogen.

Nutrient needs: Assess the overall health of your plant to determine its nutrient needs. Signs of nutrient deficiency can guide your fertilizer choice. Reference the list of signs and symptoms above to get a better idea of what your plant needs!

Growth stage: Different stages of plant growth, such as seedlings, flowering and fruiting, may require specific nutrient ratios.

Fertilizer form: Fertilizers come in various forms, including liquid, solid and slow-release granules. Choose a form that suits your application method and preferences. 

Easy, right? 

It seems a little intimidating, yes, but don’t get too stressed about it. You can always ask an online forum for extra details, or you can head to your local gardening center to ask an expert in person. 

How to actually use fertilizers

Now that you’ve picked out your fertilizer, it’s time to apply it onto your plants. It’s not rocket science, but it’s worth becoming acquainted with this fairly simple step-by-step process before actually applying your fertilizer. 

Test your soil: Before applying fertilizer, test your soil using a soil pH meter to determine its nutrient levels. This will help you avoid over-fertilization which can damage your plants.

Adjust application based on plant growth: As your plant matures, its nutrient needs may change. Make sure to adjust the frequency and concentration of fertilizer accordingly, as your plant may have aged out of its previous phase since the last time it was fertilized.

Read the label (carefully): Gotta love a generic safety warning, right? That being said, always follow the instructions on the fertilizer label, as application rates vary depending on the type and concentration of the fertilizer.

Water the plant thoroughly: Watering before and after fertilization ensures the nutrients are properly absorbed by the roots. Overwatering might wash away the nutrients, and under-watering may concentrate the fertilizer too strongly in one area.

Avoid over-fertilization: Over-fertilization can lead to nutrient burn, characterized by leaf scorch and stunted growth.

You got this!

Fertilizers play a vital role in maintaining healthy and thriving indoor and outdoor plants. By understanding the importance of nutrients, choosing the right fertilizer and applying it correctly, you can provide your leafy companions with the essential nourishment they need to flourish in your home. Remember, a balanced approach to fertilization will ensure your indoor plants not only survive, but thrive!

Have fun, green thumb!

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Featured photo courtesy Pixabay/congerdesign

Author of Article

Colleen Ford is a South African who now lives in Spokane, Washington. She loves to travel, camp (in warm weather) and bake.

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