Houseplant Fertilizer: Not So Essential

I’ve received a lot of questions lately about how to fertilize houseplants. My correspondents all seem convinced that fertilization is of prime importance in the survival of their plants. Yet that’s far from the truth. In fact, fertilization plays only a relatively minor role in the growth and health of their green pets. If you never fertilize your houseplants at all, they will still grow and even bloom. I’m not denying that their growth will be somewhat slower and their flowering, less abundant, but I think it’s important to dot the i’s and emphasize that fertilizer is not all that vital.

What Really Matters

What houseplants really need for their survival – the two most vital factors – are sufficient light and appropriate watering.

When people talk about “feeding” their plants, as in applying fertilizer, they have it wrong. The true food of all green plants is light. Thanks to the chlorophyll in their leaves and stems, plants convert solar energy into the sugars and starches they need for their growth. A plant that doesn’t receive enough light will die, often slowly, essentially starving to death. You can give it all the fertilizer you want, its days are still numbered. Of course, each plant has a preference regarding how much light it needs (full sun, partial shade, shade, etc.), but they all need light to survive.

Watering is every bit as important as light. When a plant lacks water, it often collapses very quickly. A wilting plant is physically so striking that most gardeners learn rapidly they have to water their houseplants regularly. Those that don’t figure out this rule soon declare themselves “black thumbs” and abandon indoor gardening. Of course, too much water is no better than not enough: rot can set in when plants sit constantly in soil that is soaking wet. Always follow the Golden rule of watering: wait until the soil is dry to the touch before you water again.

The proper temperature also is vital to the survival of houseplants. Place your jade plant outside in a northern winter and you’ll quickly come to understand that tropical temperatures are necessary for most plants we grow in our homes. If temperature is less often considered a major factor in houseplant care, it’s because we already heat our homes to tropical temperatures. Thus, most of us already offer exactly the temperature the average houseplant needs. Problem solved!

The fourth important factor in houseplant survival is atmospheric humidity. With the exception of succulents, most houseplants prefer humid air at all times, yet the air in our homes can be terribly dry, especially during the winter or when the air conditioning is on. In such cases, you may have to find ways to increase atmospheric humidity.

Where Fertilizer Comes In

So, I hope we all now agree that success with houseplants comes from meeting your plants’ needs for light, water, temperature, and humidity. Only when you’ve got them covered need you start thinking about fertilizer.

Why? Because plants need only very small quantities of minerals (plant nutrients) and many of them are already available to them without adding commercial fertilizer.

First of all, the potting soils you grow your plants in already contain minerals… and since potting soils slowly decompose over time, they continue to liberate even more minerals. Also, every time you repot your plants, you’re giving them a fresh supply of nutrients. Don’t forget too that tap water contains minerals plants can use for their growth. And plants also absorb dust from the air that surrounds them, dust that also contains nutrients. All those reasons explain why plants that are never fertilized nevertheless manage to grow and even do fairly well.

Fertilizer therefore is not essential to your plants. Think of it more as a “growth supplement”. It should be used in moderation, preferably only when the plant is actively growing. And when you do feel it is time to fertilize your houseplants, remember that any fertilizer will do. After all, plants can’t read fertilizer labels!