I'm frequently asked when you should start fertilizing your houseplants in the spring. It's not always an easy question to answer. Nearly all plants require a rest period in the fall or winter. During this time, you should withhold fertilizer and give your plants time to rest before they begin the hard work of producing new foliage and blooms for the following year. How long you let them rest depends on the plants.
I'll be honest with you. I let my plants tell me when it's time to begin growing. As soon as I notice a flush of new growth, I feed them a weak solution of plant food. I'm going to begin today. My red Spathiphyllum is showing a lot of active growth and I think it could use a little boost of nutrients to keep it going.
Interestingly, I have had this plant for over 10 years. It has has never flourished like it has this year. I attribute that to accidentally putting it in the right lighting. I had tried it near several windows in the home and it did okay. I finally hung it in a south window that is partially shaded by a pine tree outside the window. It did better there, but it still wasn't anything to brag about.
If your houseplants have began to show signs of new growth already, go ahead and give them a dose of plant food mixed to 1/4- to 1/2-strength - but don't forget to water them first. Applying plant food to dry soil can damage the roots of your plants.