You may have noticed that, after months of little to no growth, your indoor plants are beginning to show signs of life. Branches lengthen, new stems start to show, flower buds appear. They’re reacting to the lengthening days outside: longer days mean more energy for them, so they start to perk up and take notice. By the end of February and the beginning of March, days are now 11 hours long or even longer in most parts of the Northern Hemisphere, meaning there is now enough light to support healthy growth. That’s why this is just about the perfect time to start fertilizing them again.
Of course, some plants aren’t reacting quite yet: there are “late risers” among houseplants just as there are among humans. If so, wait a bit. Always think of fertilizer not as a stimulant, but a reward. You fertilize your plants when they show enthusiastic growth, not to try and push them into growth.
Note you can use just about any fertilizer to feed your houseplants (houseplant fertilizer, of course, but also all-purpose fertilizer, rose fertilizer, lawn fertilizer, etc.): plants really don’t much care about specific formulations. The important thing is simply to never exceed the recommended dose.