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What Is The Difference Between Organic and Synthetic Fertilizers?

It’s pretty easy to get overwhelmed by all the options in the fertilizer aisle! While it may appear all the packages are repeats of one another, the real difference comes down to the ingredients and how they are sourced. You may notice that one fertilizer for tomatoes has a completely different ratio of numbers compared to another bottle of tomato fertilizer from a different company. These differences are usually due to the fertilizer being organic or synthetic! But… is one better than the other?

What do the numbers really mean?

The ratio or numbers you’ll see on the label of your fertilizer represents three macronutrients (Nitrogen-Phosphorus-Potassium, or N-P-K). A good way to remember the functions of these macronutrients is: “Up, down, all around.” The first number (nitrogen) primarily impacts green, above-ground growth. The second number (Phosphorus) primarily impacts below-ground root growth, and the third number (potassium) is useful for a great variety of plant functions. These numbers also measure the macronutrients that are readily available at the time of application – we’ll come back to this in a moment.

You may notice that organic fertilizers tend to have smaller numbers than those featured on synthetic fertilizers. This is because synthetic fertilizers work as a “one and done” or a “one punch” method. This means that these fertilizers only contain the readily available nutrients measured on the label (and nothing more). Since it’s readily available, the plant will use up all the N-P-K provided at the time of application (essentially). 

Organic fertilizer works differently, however. While they typically have a lower concentration of readily available macronutrients, their organic makeup generally cause more macronutrients to become available in the soil over time, through nutrient transfer and bio-chemistry. So while your plant receives the immediate benefit of readily available nutrients from an organic fertilizer, it also receives the benefit of additional macros over time. It is also important to note that organic fertilizers often contain many micronutrients in them that will benefit your plants on top of the N-P-K already in there! These micronutrients also support soil health, feeding many of the smaller microbes and beneficial bacteria that keeps your soil “living” – which your plant benefits greatly from. Don’t be fooled into thinking that, just because organic fertilizers have smaller numbers than synthetics, they may be “weaker” or not as effective! They are powerful and beneficial, especially over the long term. If you’d like to learn more about how macronutrients and micronutrients work, check out our blog post: What Are Those Three Numbers On Your Fertilizer And How Do They Work?

What is in my fertilizer?

So, we know now that fertilizers contain three macronutrients; but where does that nitrogen, phosphorus, and potassium come from? In organic fertilizers, the nutrients come from organic materials such as digested kelp, composted forest matter, and even manure! In synthetic fertilizers, the nutrients are created by humans by making compounds containing elements and produced in a lab. It is important to know that with synthetic fertilizers you are feeding the plant; with organic fertilizers you are feeding the soil! You must follow the application directions for synthetic fertilizers closely as when applying them you may run the risk of burning your plants if not done properly. Organic fertilizers are more forgiving, it is very hard to burn or overfertilize a plant while using one!

What are you fertilizing?

  Depending on what you’re fertilizing, the fertilizer you choose can differ. Due to our short growing season, for annuals and pre-done potted and hanging basket arrangements we may recommend a synthetic fertilizer since the goal would be to quickly perk up those flowers, promote constant blooms, and keep the foliage green – rather than the goal being the long term health of the plant, as we only tend to enjoy annuals for a couple of months. 

  Trees, shrubs, and perennials would benefit from an organic fertilizer as they tend to spend their lifetime in the spot they are planted in. Due to this, we want to ensure the soil is healthy and the plant has everything it needs to thrive in that spot! 

  Annual fruit and veggie plant fertilizers can go either way depending on your preference and how they are planted. In pots and raised beds, fruits and veggies can be fed with a synthetic fertilizer as these plants and most of the soil will likely be composted at the end of the season. For vegetable beds and larger planter boxes that you may not change the soil often, we may recommend organic fertilizer as you will want to feed the soil as well as the plants. You may also wish to opt for an organic fertilizer, as you are consuming the fruit from these plants!

Finally, indoor plants tend to benefit most from an organic fertilizer, as we want to promote optimum soil and plant health all year long. They are in a controlled environment, and likely don’t get repotted often.

*Hot Tip: Potatoes, specifically, are very heavy feeders. When growing, we recommend changing where they are planted each year or changing out the soil if possible! If not done, you may notice in the years to come that your potatoes will have scab. *

  To conclude, neither synthetic nor organic fertilizers are better, per say. There are pros and cons to both methods of fertilizing, and situations where one or the other is appropriate. It really comes down to the plant, the needs, and your personal preferences!

Some of our Favourite Fertilizers:

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Eden Younger
Eden has been a member of the Anything Grows team for six years. She has a passion for house plants but also loves expanding her knowledge of horticulture and the needs of outdoor plants!

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