Normally, in temperate regions where winter nights are very long and days very short, it’s best to stop fertilizing houseplants in October. After all, many of them simply shut down at that time of the year anyway. They may not all go totally dormant, but their growth is often at a standstill or at least excruciatingly slow. Some do continue to keep on growing despite the decrease in lighting, but it’s better not to encourage them to produce off-season growth by applying fertilizer. That tends to result in pale, weak, etiolated growth: not what you want. I actually prune most winter growth off my houseplants: the new growth to come in spring will be much more robust!
(Gardeners who grow their plants under lights can continue to fertilize their houseplants year-round, as long as they contain to maintain 12-hour days or longer.)
Spring Has (Almost) Sprung
But with the return of longer days in late February and early March, many plants show clear signs of growth. No, it’s not summer yet, but with more than 11 hours of daylight per day (and that number increasing daily!), they’re starting to awaken and put on growth. And it’s when plants are growing that you need to fertilize them.
Use Fertilizer as a Reward
Remember that the fertilizer should never be given to stimulate growth or flowering (there is too much risk of applying it when the plant is unable to use it), but instead as a reward. So, you should start fertilizing houseplants that show signs of renewed growth. (You’re growing? How lovely! Let me feed you!)
For some Northern Hemisphere houseplants, growth will have begun before the end of February, so fertilize those first, yet you’ve probably noticed others that aren’t quite ready yet. They may only start to signs of growth in mid- or late March. If so, wait a bit longer. Always follow the plant’s lead: it will “tell” you when the time to fertilize has arrived.
Which fertilizer should you use? That is of almost no importance. Just use whatever you have on hand. Read Plants Can’t Read Fertilizer Labels to learn more.
Always Fertilize Lightly
The important thing is to always fertilizer lightly, probably at a much lower dose than that recommended on the product label: one quarter to one eighth of the recommended dose is sufficient for most plants grown indoors. The concept of “growth booster” type fertilizers, heavy on minerals and supposed to stimulate a faster recovery, is a marketing gimmick used to sell more fertilizer. Plants prefer to receive their fertilizer gradually, not to be flooded with more minerals than they can possibly use in a short period.
So, no rush, but if your houseplants are presently showing signs of growth, it’s time to start fertilizing them again! And certainly, most dawdlers will ready for a few extra minerals by the end of March!