Note: I republished this blog with permission from Folia Design, a Quebec City houseplant boutique. The author is Réal Dumoulin. I did the translation from French into English.
I must admit I was impressed with the article from the start, but all the more so when I realized the author had quoted me! (How often does that happen!) So, just maybe that influenced my desire to republish this … but I like to think I did so simply because it’s a really great article that covers a complicated subject quite succinctly.
There are many myths circulating about the importance of fertilizing plants, especially houseplants. Most people think that fertilization plays a major role in the health of their plants when in fact it’s only a minor factor in their development. What matters most in the life of a houseplant is the quality of the soil, lighting, watering, humidity and ambient temperature. However, that doesn’t mean you can completely neglect fertilization either: it still plays a small role in the quality and beauty of our indoor plants.
When Should I Fertilize?
The main rule is to only fertilize a plant when it is actively growing!
- In general, you don’t need to fertilize plants during the winter in the average home. Most will be semi-dormant and fertilizing then would only stimulate weak and etiolated growth, susceptible to insects and diseases. However, starting at the end of February, the increasing luminosity leads to a growth spurt in most indoor plants. That’s a sign it’s time to fertilize.
- However, there are exceptions. Any plant that is clearly growing in the winter can be fertilized, although normally at a lower rate than the one recommended on the fertilizer label, say at about ¼ to ½ of the usual rate. Plants that are getting especially bright light, for example under fluorescent lights, in a solarium or in front of a south-facing window, may continue to grow and even bloom during the winter and they’re the ones that will likely need fertilization. In addition, some plants, such as cyclamens, houseplant azaleas, gardenias, etc., are naturally in full bloom during the winter, and therefore need regular fertilizing at that season.
- One common error is fertilizing a plant when it’s clearly in distress, something you should always avoid! When a plant is in bad shape, you need to analyze the situation and treat it according to its needs. Is it receiving insufficient light? Too much or not enough water? Is its soil too compact? Is it contaminated with mineral salts (unabsorbed fertilizer from past treatments)? Fertilizing a plant in distress may out-and-out kill it!
- Generally, you won’t need to fertilize after repotting or top dressing, because the potting mix used already contained fertilizer. Wait at least 2 to 4 weeks before starting to fertilize a plant after either treatment.
- Plants won’t usually need fertilizing for about 6 weeks after purchase, as they were likely treated to a good fertilizing regime in the store.
The normal period for fertilizing houseplants is from the end of February to the month of September whether they spend the summer indoors or out.
Which Fertilizer to Choose?
Stores offer a huge number of different fertilizers in stores and they come in different forms and formats, plus they can be chemical or organic. Naturally, you’ll want to choose the best for your plants.
However, it’s important to understand that most fertilizers are about equally good and you can use almost any one on any plant. Garden writer Larry Hodgson rightly points out that plants can’t read fertilizer labels. In other words, they’ll do fine no matter which fertilizer you use.
Slow-Release or Quick-Release Fertilizers?
Some fertilizers are in the form of granules or spikes and are slow release, that is to say that they’ll fertilize the plant over a long period. Often, a single spring application is sufficient, although a second one in early July may be useful.
Most fertilizers, though, are quick release and come in either liquid or powder form. They’re designed to be diluted in water before use, according to the manufacturer’s instructions. Just water the plant’s potting mix with diluted fertilizer, although it’s best not to fertilize plants when their soil is dry, as this can harm the plant’s roots and, eventually, the plant itself.
Foliar fertilizer is yet another kind of fertilizer. It’s designed to spray directly on the foliage and yes, plants do absorb fertilizer through their leaves. Often, liquid seaweed, properly diluted, is used as foliar fertilizer.
20-20-20? / 10-30-10? / 15-30-15? / 30-10-10?
Oh my! All those numbers! What’s a houseplant enthusiast to think? But remember from above that plants can’t read fertilizer labels and really don’t care what you use! In general, a balanced fertilized like 20-20-20 or something similar is ideal for all plants. Liquid seaweed fertilizers are particularly interesting for both foliar use and for watering into potting soil.
What About Compost?
Compost is not really a fertilizer, but a product that improves the soil’s structure and texture so that it better retains water and fertilizers. By all means, do add some to your potted plants, but you’ll still need to fertilize at some point.
Should I Use Organic or Chemical Fertilizer?
People have a wide range of opinions on that subject, but in fact, plants really don’t care which type you use. The choice will likely be based more on your personal values than on the plant’s needs. You can easily find organic fertilizers such as liquid seaweed if that’s what your choice.
Many people use too much fertilizer, thinking that the more they give, the more beautiful and healthier their plants will be … and that’s a serious mistake! Far more plants die of over-fertilization than a lack of minerals. Excess minerals lead to tall, unhealthy growth and leaves plants susceptible to diseases and insects. In addition, the excess leads to mineral imbalances, harming the plant even further.
In short, a balanced fertilization you apply according to the plants’ needs will help your houseplants grow and flourish … but any excess will be harmful.
Great post. Can’t agree more with using any fertilizer and the fact that plants can’t tell the difference between synthetic and organic.
I am less convinced about “it’s best not to fertilize plants when their soil is dry, as this can harm the plant’s roots and, eventually, the plant itself.’ I would want to see evidence of that, but I also have no knowledge saying it is not true. Is that another myth that needs to be debunked?
You’ll note I didn’t actually write this one, but I thought it was really quite good, so translated it and republished it. But I personally don’t hesitate to apply fertilizer when I water a dry plant. So yes, it could well be another myth to look into. My concern would be when someone waters a drought-stressed plant with dilute fertilizer, but not fully moistening the root ball. That might just stress the roots even further. I’m sure you and I would always water a drought-stressed plant abundantly, moistening the root ball through and through.