After spending several months in the winter doldrums, by early March (in the Northern Hemisphere at least), your houseplants are starting to come back to life. Buds form, new leaves unfurl, flowers appear. They are, in fact, reacting to the increase in sunlight, which is both more and more intense and of longer and longer duration.
This return to growth influences—or should influence—your way of caring for them. First, you can start fertilizing them again, something you probably stopped doing back in October. Also, tis the season to start thinking of taking cuttings, pruning, dividing and repotting, all best done when plants are growing actively.
The Annual Repot
Let’s talk specifically about repotting.
Most indoor plants do best when repotted annually. They have increased in size over the last year and will appreciate a bit more space for their roots. For slow-growing plants, like most cacti and other succulents, plus orchids, repotting every two or three years will suffice. For young plants in small pots, though, repotting twice a year, in spring and again in early fall, may be necessary.
In addition to giving more space to plant roots, repotting into fresh potting mix solves a basic indoor gardening problem: it eliminates the mineral salts that have accumulated in the soil. Such salts are naturally present in water and are even more concentrated in fertilizer. In small quantities, most of these minerals are actually good for plants: they use them for their growth! Outdoors in most climates, any unused minerals are leached out of the soil by rain and so don’t accumulate. In pots, however, there is no outlet for minerals that start to build up, because excess water doesn’t drain away, carrying excess minerals with it, it evaporates. Thus, these minerals remain in the potting mix and start to accumulate, especially near the top of the rootball, sometimes forming a white or yellow crust on the side of the pot, on the plant’s stems of and on the surface of the mix.
These surplus minerals slowly build up to toxic levels, damaging the roots near them and even killing stem cells. Repotting helps greatly to remove built-up minerals. But what can you do when repotting is impossible?
And there does come a point in the life of some plants when repotting into a larger pot is simply not feasible. They’ve grown to such a size that repotting is too much work. Can you even imagine repotting an indoor ficus tree in 20-inch (50 cm) pot … or even finding a larger pot? But then what are you to do then when mineral salts build up?
Top Dressing to the Rescue
One easy solution is top dressing. Mineral salts mainly accumulate in the top inch or so (3 cm) of growing mix, so you can remove the contaminated soil on the surface and replace it with fresh soil. Deeper down, the soil is usually still of decent quality. Top-dressing is not quite as good as repotting, but it comes pretty close!
How to do it?
You have to scrape off the top inch or so (about 3 cm) of soil. Whatever tool you want to use is fine: a hand cultivator, a trowel, a houseplant rake, etc. I just borrow a fork from the kitchen to do the job. Once you’ve removed the top layer of soil (put it in the compost bin: the minerals will give compost microbes a real boost!), all you have to do is to replace it with a fresh layer of potting soil. Finish up with a good watering and you’ve just given your plant a whole new lease on life!
Can you keep top dressing indefinitely? Logically, it would be wise to repot even a very big plant at least every five years. However, I have indoor trees that I haven’t repotted for 20 years and that are doing very well with just an annual top dressing.
Try top dressing to revive your tired houseplants. At least, if you just aren’t able to repot them. You’ll soon see a difference in their performance!