While you may be very busy tending to your outdoor gardens, this isn’t the time to ignore your indoor potted plants. In fact, this is the perfect time to check them for repotting, because they are reacting to spring just like the outdoor garden and we need to help them with room to grow … rootwise.It’s generally thought that potting and repotting is a late winter or spring job, but when you consider that most of our houseplants have their genetic and geographic heritage from places very close to the equator, then this can be debated. Even though these plants are growing in northern latitudes, their biological clocks can often be controlled by genes as well as our weather, and you may be surprised to see sudden spurts of growth until the indoor environment—low humidity and low temperatures—slows them down. But many of these plants have been grown north of the equator for uncounted generations and now, when summer approaches, mine want to stretch and grow. For many this means repotting, for as they grow above ground most need to grow below in the pot as well. It’s called the root/shoot relationship.
Some plants, however, thrive best when they are on the verge of bursting their pots. Agapanthus will literally burst a clay pot in time and for this reason you will often find them growing in wooden pots (indeed they seem to bloom best when severely pot-bound), but other tropicals such as amaryllis, crinum and ornamental asparagus crowd their pots to the point where the plant actually pushes up and over the pot rim. These plants should NOT be repotted regularly, as this tight situation is important for maturation and flowering. Although watering may become difficult, if they are constantly potted up, they will never perform as advertised.
As a very general rule, repot a plant whenever it outgrows its present pot until it reaches a size or condition that pleases in terms of either space available or your aesthetic requirements. A good sign that a plant needs repotting is when you water it one day and it’s wilting or drooping the next. The popular Ficus benjamina or weeping fig will fill a pot and if not repotted will drop leaves and continue to drop leaves until it has a larger pot.
Once it is repotted, maintain the plant in a healthy condition with adequate feeding and pruning (including root pruning if you choose to keep the plant at its present size) without repotting ad infinitum. Occasionally, a plant refuses to thrive in the preferred pot size despite your maintenance efforts and then you have to examine your cultural practices. Some problems develop when the root system becomes so dense that there is no room for water absorption in the soil and the water just sits in the saucer or slips though the pot.
As to the types of pots, there are very important differences between clay, plastic, foam (faux terra-cotta) and glazed ceramics, and if you treat a plant the same in a plastic pot as in a clay one … you’re bound for a pile of mush. Pot color also comes into play. While you may prefer a white plastic pot, the plant’s roots prefer the darkness of black or green. Consideration also has to be given to the location of the plant and the pot color. A dark-colored pot outdoors in a sunny spot or indoors on a sunny windowsill will absorb the heat of the sun and cook the plant’s roots. However, a light-colored pot will reflect the light and heat, keeping the soil cooler and thus moister as well. Also, moving a plant from clay to plastic or the reverse needs to be done with some caution based on the water retention of the differing pot compositions.
Because they are lightweight, plastic pots are often used for hanging baskets. They are easier to clean and retain moisture longer, a quality that endears them to commercial growers, but can result in doom if you are heavy-handed with the waterspout. When a plant is a heavy drinker, such as an azalea, geranium or cyclamen, plastic pots are useful if you hate to water. But leave a cyclamen or African violet in a plastic pot that has too much water and in only a few days it will begin to rot.
Ceramic pots, since the clay base has been sealed by the glazing, should be treated as if they were plastic, as the glaze will inhibit any movement of moisture through the sides of the pot.
You can mitigate the tendency of a plastic pot to retain moisture by adding additional drainage, using gravel on the bottom of the pot or sand added to the potting mix. And if you insist on a clay or terra-cotta pot for a plant that needs a great deal of soil moisture you can add organic matter to the soil mix and that will retain additional moisture.
Adding gels or water-retaining additives called hydrogels to potting soils to reduce watering has had some soggy and sad results. They were very popular a few summers ago when it was hot and dry all season. Gardeners and landscapers added these materials to planters, outdoor potted plants and hanging baskets and when the weather turned rainy the soils swelled, and in some cases the super-saturated soils were seen oozing out of pots, dripping from hanging baskets and leaking from planters.
For large plants and plants whose root systems like to “breathe,” clay pots are the most desirable. Clay’s porous nature makes it ideal for cacti, many orchids, bulbous plants and plants that like growing with cool roots in high temperatures. The ability of moisture to move through the porous pot actually has a cooling effect similar to evaporative cooling. Orchid growers, though, have learned to live with plastic pots by changing the potting medium to a much more porous one that holds little moisture, thus compensating for the lack of “breathing” of the plastic pots that most orchids are now sold in. Plastic also makes the plants less expensive to ship, but the fact that orchids are sold in plastic doesn’t necessarily mean they thrive in plastic.
Next week, how to repot and the easiest, most ridiculously easy, way to do it. In the meantime look for those dropping leaves, roots growing from drainage holes and plants that simply look top heavy. Remember, roots are not only anchors but an important part of the plant’s ability to transport water and nutrients. Take care of what’s in the pot and the plant above will be much happier. Keep growing.