Fertilizer 101: Some Common Pitfalls to Avoid

One of my earlier mistakes in gardening was regarding the use of fertilizer– either from too much of it or too little.  I had been too eager to see immediate results for my seedlings, that I practically bought every single product that had the words “organic fertilizer” on the label. Later on, I realized that I only needed a few basic ones,  and the rest were simply redundant. In fact, I also discovered that I didn’t have to buy since I could produce them from my own kitchen scraps ( See my blog post “DIY Organic Fertilizer from Kitchen Scraps“).


Fertilizer 101:  The basics of  plant nutrients

Before I share with you my own blunders (so you can avoid them),  allow me first to go through the basics of  plant nutrients. This is just a recap of our high school biology class, in case you hadn’t paid any attention to your teacher’s lectures then.

Plants need their regular dose of nutrients from the atmosphere and from the soil. There are six primary nutrients that our plants need for them to function properly – i.e.. grow leaves and produce food. Carbon, hydrogen and oxygen are the first three nutrients which plants can get from air and water.  The other three are nitrogen, phosphorus and potassium. These nutrients are largely found in the soil and they can get depleted over time as plants feed from the soil.

Eggplant grown in potEach type of nutrient serves a purpose. Nitrogen (N) helps plants produce new tissues, and it is responsible for the growth of new leaves. Phosphorus (P) stimulates root growth, helps plants set flowers and also improves yield for fruit bearing plants.  Lastly,  potassium (K) helps improve overall vigor, inducing plants to produce more carbohydrates (thus bigger fruits), and improves resistance to diseases.  By using fertilizer (whether organic or synthetic), we replenish these nutrients found in the soil.

Most fertilizers that we find commercially have all these 3 elements- usually in varying proportions.  The numbers that we see  on the label  (for example, 10-10-10, or 20-10-10)  indicate the  ratio of each of these fertilizers in this order N-P-K. For instance 10-10-10 means equal amounts of nitrogen, phosphorus and potassium, while 20-10-10 means that there is twice as much nitrogen content than the other two elements.  This serves as a guide for us gardeners so we can choose which fertilizer to buy — whether to grow more foliage or to produce more flowers and fruits.

Aside from these major nutrients, there are also other nutrients that plants need, but in much smaller quantities. These nutrients are calcium, magnesium, and sulfur.  Generally, these plant nutrients help them in their processing and production of chlorophyll.  In addition, there are eight micro-nutrients that plants need in very tiny quantities; such as boron, copper and iron, to name a few.  Any soil that is rich in organic matter usually contains sufficient amounts of these micro-nutrients.

Common mistakes when applying fertilizer

Understanding the basics described above will help us avoid these common pitfalls in the use of fertilizers.  Let me share with you the top 5 most common mistakes that I committed earlier as a beginner in gardening (Up to now, I still make these mistakes occasionally!!!).

Mistake #1.   Overdoing it.

In my eagerness to grow the plants faster, I had spent (and wasted) a significant amount of money on various fertilizers, especially during my early gardening days. I must have tried every single brand that I found in the store without knowing which ones really worked.  Some organic brands even prescribed an expiration date which meant  that I had to discard them before being able to consume at least half of the contents.  Such a waste indeed!

Mistake # 2. Treating all plants the same.

Not all plants are the same, so before applying fertilizer,  it is best to understand first the nutrient needs of your plants.  As a rule, plants that you grow for the leaves need more nitrogen, while those that you grow for flowers and fruits need a higher dosage of phosphorus and potassium.

Fertilizer on tomato plantsSome plants require more fertilizers than others. However, plants grown in containers (like mine) need a little bit more than the usual regular  application of fertilizers because the soil nutrients in the containers get depleted faster.  Tomato plants and eggplants, for example, are heavy feeders, so I try to add a handful of organic matter or compost every other week, especially during their  fruit-bearing stage.  Most herbs like basil can thrive with less fertilizer requirements, but I do apply compost every other month and organic foliar spray once a month for healthier leaves and better resistance to disease.

Mistake # 3.  Forgetting about the other basics.

Marigolds grow best with lots of sunshine, not just fertilizer.

When I first tried growing marigolds, I noticed that after two months, they were not producing flowers as they should. So I applied more fertilizer, each time experimenting on a different brand. After another month, the plants grew healthier foliage and still no flower buds.  Finally,  when I decided to move the pots to a sunny spot, that’s when they started to set flowers- lots of  tiny flower buds.  All along, my marigolds simply lacked sunlight (6 – 8 hours) for them to set flowers.  Adding fertilizer did not really help much because it only induced the marigolds to focus on growing leaves, and not flowers.

Mistake # 4. Failure to read the labels carefully.

Synthetic fertilizers often produce immediate results for plants, sometimes within 24 hours.  It’s always so tempting to add a little bit more.  However, an overdose of synthetics can burn the plant roots  and eventually stunt their growth.  So when using synthetic brands, read the labels carefully and apply sparingly.

Mistake # 5.  Growing impatient.

Lastly, be patient. Note that the effect of some fertilizers (especially the organic ones) will not show immediately. For instance, if you apply coffee grounds, it will take a number of  days to see the results because the grounds have to decompose and convert to basic organic nutrients. While fertilizers can help boost plant growth or production, remember that at some point,  it’s always best to allow nature to take its normal course. Forcing your plants to grow or bear fruits with the use (or over-use) of fertilizers might even be detrimental to your plants’ health in the long run.

Happy gardening everyone!

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About Glo de Castro

The author is a lawyer and an executive in a leading real estate company in the Philippines. Urban gardening is one of her hobbies and passion. She created this website because she loves to write about her gardening experiences and share them with fellow gardeners. She also conducts seminars about urban gardening occasionally.

Thank you. Your comments are valuable to me to help me improve my blog posts. Cheers.