When a houseplant remains too long in the same pot, the soil it grows in becomes contaminated with mineral salts. You can see them because they form a white or yellowish crust on the inside edge of the pot and even on the lower part of your plant’s stem. Theoretically you should repot a plant whose soil is contaminated, or at very least, leach the soil. But there are situations when repotting or leaching is difficult or impossible. For example, when the plant is in a pot so big that transplanting it or even moving it to the sink for leaching is going to be a major hassle. Or, when you have a climbing houseplant that is working its way up your indoor wall… or when the pot is permanently bolted to a floor or wall. Under these circumstances, what can you do to keep the plant in good condition?
Fortunately, there is a way to keep a plant in the same pot for 5, 7, 10 years or more: you just have to top-dress! This involves scratching the top 1 to 2 inches (2-4 cm) of growing mix and adding the harvested soil to your compost bin, then replacing it with a fresh layer of potting mix. This will help because toxic minerals tend to migrate upwards to the top of the pot: by replacing the contaminated portion of the soil with fresh mix, you will allow your plant to remain in good condition even if you don’t repot.
The usual tool for top-dressing is a fork. Of course, I don’t mean a garden fork, but simply one borrowed from the kitchen. If you have one of those houseplant tool kits that people routinely give as a gift, but that no one every uses, the mini rake it contains would also work fine. Aren’t you glad you finally found a use for it!
When should you top-dress? Any season will do, but you will see results faster if you do it in early spring. That’s because your plant will be ready to begin its annual growth spurt at that time of year and a fresh coat of soil will signal it that it’s time to begin.
After your first top-dressing, mark it on your calendar for next year and make it an annual routine. After all, what wouldn’t you do to make your houseplants happy?