How to feed a hungry houseplant

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Audrey, the plant in Little Shop of Horrors, liked to dine on humans. But fortunately, most houseplants do just fine with ordinary plant food

Of all the basic care requirements for maintaining a healthy indoor plant collection, perhaps the least understood is how, when and how much to feed them. But if you want your green babies to thrive over the long term, regular feeding is a must.

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Houseplants can and do survive without being fed; but over time, they will start to show signs of stress. New growth will be slower, weaker, or even stop altogether. Eventually, the plant may fade and possibly even die.

This could just be me, but I’ve noticed that the soil in a plant that’s never been fed doesn’t look right as well. It’s either compacted or simply appears exhausted (because it is).

All plants – house, garden or wild – need three nutrients to survive: nitrogen, which helps build strong leaves and stems and is needed for making life-giving chlorophyll; phosphorus, which promotes healthy root production; and potassium, for flower and fruit production and overall sturdiness.

There are different fertilizer formulations available that vary the proportions and percentages of these three nutrients (identified on the package as N, P and K, respectively, and a set of numbers like 3-5-7).

A high-nitrogen (N) formula will boost leaf production; fertilizer with a higher potassium (K) number will encourage large blossoms and fruit, while a high-phosphorus (P) formula boosts root production or supplements plants with few to no roots, like bromeliads.

But don’t be put off by all the choice. A balanced fertilizer – say, 20-20-20 – is fine for most houseplants. In fact, look for “houseplant food” at the garden store and you’ll do fine.

I personally prefer liquid plant food. The brand I like comes in a concentrate, but others come in powder or granular form. Whichever type you buy, you basically just mix it up with water in a watering can – carefully following the proportions specified on the label – and pour it on the soil, just like regular watering.

You can also get pellets or sticks that you stick in the soil, foliar sprays (which do miracles for a hungry plant, since the nutrients are absorbed almost immediately), or supplements that you can add to potting mix when you repot your plants.

The only problem with each of these options is you can’t control the amount and consistency of the application as well as you can with a water-based solution. And too much fertilizer, or a concentrated pocket of it touching a stem or a root, can burn or even kill your plant.

Okay, when and how often should you feed? The first point to remember is you should only feed your plants when they are actively growing. When they show signs of slowing down, usually in the fall, put the fertilizer away till spring.

Also, you don’t need to feed newly purchased plants for at least a couple of months after you buy them. Chances are the grower has turbo-charged them with fertilizer, so they’ll look all bright-eyed and bushy-tailed when they arrive at the store and entice you to buy them. And if you’ve just repotted a plant and added fresh new potting soil, you’re good to go for at least a month or so.

The liquid food I use suggests you apply it about every four weeks, but read the label of whichever type you buy and follow the instructions. Don’t go overboard and overfeed, which can cause problems as well (frustratingly, similar to insufficient feeding: spindly growth and weak stems).

Once you’ve been doing it for a while, you’ll get an idea of what works best for your plants – and there is absolutely no danger they will suddenly rise up and devour you.

Please feel free to write in with questions, to comment or to share your own city gardening adventures
with Martha. Write to her at marthasgarden07@gmail.com.