Part of me wonders if fertilizing is really necessary or if it’s all just a big marketing ploy. I guess it makes sense that houseplants – which live in a controlled environment in a pot – would need fertilizer, since they have no other inputs other than sun and the water you give it. I happen to have some old fertilizer on hand, so I’m going to use it.
The fertilizer I have is Miracle-Gro All Purpose Plant Food. My mom had bought this stuff probably over 20 years ago, and it’s been sitting under our kitchen sink doing nothing.
To educate myself about fertilizing my plants, I watched Summer Rayne Oakes’s YouTube video on this topic. Here are some things I learned from her video:
- To be called a fertilizer, the manufacturer must guarantee a certain amount of nitrogen (N), phosphorous (P), and potassium (K) in the product. If the amounts of N, P, and K in the product are not precisely quantified, the product would need to be called a “soil amendment” or some other euphemism for fertilizer.
- N-P-K ratios are actually the percent-by-weight of the product that are N, P, and K. So, if a fertilizer says it is “20-10-10”, then 100 grams of the fertilizer would contain 20 grams nitrogen, 10 grams phosphorous, and 10 grams potassium. The other 60 grams are “filler.”
- Organic fertilizers are not as strong as synthetic fertilizers. They will have much lower N-P-K numbers (for example, 2-3-3) as compared to synthetic fertilizers (e.g. 20-20-20). Synthetic processes can concentrate the elements much better than any natural/organic process. Stronger is not necessarily better (see #8).
- Organic fertilizers may also contain beneficial bacteria or fungi to help the soil. There are also other micronutrients (like calcium or iron) in some fertilizers – either organic or synthetic.
- Nitrogen is necessary for making chlorophyll, and therefore is supposedly good for promoting strong foliage on plants.
- Phosphorous is good for flowering plants. It’s a “bloom booster.” (Other sources say phosphorous is necessary for genetic functions and energy storage, and thus a plant low in P will be slower to mature. This makes sense, I guess, since phosphorous is part of DNA and ATP.)
- Potassium is good for…generally strong plants? According to wikipedia, K is needed to “provide the ionic environment for metabolic processes.”
- Less is more. Plants only need *tiny* amounts of N-P-K, and you can do more harm by over-fertilizing than under-fertilizing.
- You only need to fertilize during the plant’s growing season (spring and summer for me).
Miracle-Gro is a synthetic fertilizer that is heavy on the nitrogen and potassium: 24-8-16. It’s “Guaranteed Analysis” says it also contains the following micronutrients: boron, copper, iron, manganese, molybdenum (0.0005%), and zinc. (Side note: Apparently, Miracle-Gro is owned by the makers of RoundUp.)
The instructions say for houseplants use a mix of 1/2 tsp Miracle-Gro per gallon of water on your plants every two weeks. So that’s what I did.
I actually watched Summer Rayne Oakes’s video after I put the first fertilizer on my plants, and she recommends using half the recommended strength when using a synthetic fertilizer because of the risk of over-fertilizing. She also doesn’t fertilize nearly as often as the manufacturers suggest.
It’s been about 5 days since I fertilized my plants, and so far they seem ok. They don’t look like they’ve been “burned” (over-fertilized), but they also haven’t had any miraculous growth spurts. Shucks.