Repotting: Cozy new quarters for plants

Some houseplants become so large that the roots outgrow the pot. When that happens, growth can be stunted. Water may flow right past the roots before they have a chance to absorb it or gather nutrients from fertilizer.

How do you tell if a plant is root-bound? It may quit growing. Water may flow quickly out the drainage holes with no pause for absorption. Or you may see roots on the soil surface or growing out of the holes.

To avoid unnecessary trauma, don't repot a plant unless it needs it. Many plants will grow happily for years in the same pot and soil with proper fertilizing.

The ideal time to repot is early spring, so the plant has a whole season to reestablish its roots. But it may be convenient to do it now, as you begin to bring houseplants back indoors. Because the plant is heading toward winter dormancy, it will take more time to resume growing.

Here are the steps in repotting a houseplant:

Confirm that it needs repotting. Gently remove it from the pot (don't yank). If roots fill the pot, are circling or are growing out of the holes, the plant is root-bound. If the plant has cracked or stretched the pot, it is too crowded.

Choose a new pot. It should be just one or two inches larger in diameter. A too-large pot may trap excess water around the roots and lead to rot. Use a potting mix appropriate for your plant, such as cactus mix for cacti and sterile soilless potting mix with plenty of organic matter for most houseplants.

Is the plant crowded? Gently pull or cut the roots apart to make two or more divisions, to be replanted separately.

Hold in the soil. To keep soil from washing away, cover drainage holes with fiberglass window screening. For a pot with one hole, use a shard of broken crockery or a bottle cap. Don't add a layer of gravel or pot shards; it reduces drainage.

Make a base. Place a handful or two of potting mix in the bottom of the new pot. Break up the plant's mass. Gently tease the roots apart to stimulate them to grow out. Fleshy or tough roots may need to be cut with a clean, sharp knife.

Set the crown (where the plant meets the roots) at soil level. Fill around the roots with potting mix and tap the pot gently to settle it. Make sure the top of the mix is even and one inch below the rim, to allow watering space.

How do you get a houseplant through the winter?

The most important step is knowing what kind it is so you can find out what it needs. A tropical forest plant such as a philodendron needs care different from a desert cactus. But here is some advice that applies to many common foliage houseplants native to tropical or semitropical areas:

Light: Indoors, plants get a fraction of the light available outdoors. Only the sunniest window (or a plant light) will provide enough energy for a plant to bloom. In most houses and apartments, stick with foliage plants that can handle shade. Read the label to make sure you can meet the plant's light needs.

Water: Don't water on a set schedule; plants and pots vary, and watering too much is as bad as not watering enough. Check the soil moisture by sticking your finger in an inch or two. Water if you don't feel dampness. Or heft the pot to see if it feels light. Half an hour after each watering, empty surplus water from the saucer or decorative cachepot; roots left sitting in water will rot.

Fertilizer: Potting mix provides few nutrients. Use a water-soluble fertilizer labeled for houseplants (organic ones are available) at half the rate suggested on the label. Fertilize every couple of weeks during spring and summer, but just once a month or less during fall and winter, when the plant is dormant. Potting mixes containing slow-release fertilizer will reduce the need to fertilize for a few months but not eliminate it.