Repotting rootbound plants can save water and work

The simple act of repotting rootbound plants into larger containers can reduce the need for watering from once or twice a day to once or twice a week. This is particularly true if you move them from porous to nonporous pots. Plants with larger root areas are also less prone to damage by drought.

As a bonus, you get champion-size plants faster; like the fern shown at right, most common container plants quickly expand to fill new root space.

The traditional wisdom was to increase container diameter no more than I to 2 inches at a time. That advice comes from the days before modern lightweight, fastdraining potting soils made it easier not to overwater container plants. In those days, people also had more space to store pots of all sizes, and time to transplant several times a year.

Now standard practice among professionals is to move most plants up several pot sizes at a time: from 2 1/4 -inch pots to 6inch or gallon containers, then to 10-inch or 5-gallon containers, then to 15-gallon containers. However, you do need to keep the following guidelines in mind.

Most plants thrive in bigger pots Skip more than two pot sizes only with plants that are moderate to fast in growth rate, that fill their current pots with roots, and that thrive on regular watering. These include ferns, geraniums, most perennials, and many shrubs.

Nurserymen repot year-round, but the best time is just before or during active growth (usually between late winter and midsummer; otherwise, there's a longer wait for plants to fill out).

As a size guage when choosing a new pot, select one that's at least half as wide as the plant's leaf spread (in the ground, a plant's roots usually spread the full width of the leaf canopy or even wider). That way, the plant will look in reasonably good proportion to the pot right away. Using this gauge with the fern pictured here, we moved it from a 7-inch-diameter pot up to a 12-inch one.

But some plants can't take such a big jump in pot size

Two groups of plants should not be moved to pots more than the traditional few inches larger: young plants whose roots just barely fill their present container and drought-tolerant plants that tend to die when overwatered; these include bottle palm (Beaucarnea), other palms, cactus, and cycads.

Still another reason to increase pot size in small increments is if you have a tendency to drown plants by overwatering.

To relieve heat or drought stress for plants that are very young, can't tolerate frequent watering, or perform best with confined roots, the best method is to double-pot. As shown below, use a pot several inches larger in diameter than the one the plant is in, and fill the gap between the two pots with sand, fine gravel, or soil. For additional cooling, wet the soil in the outer pot.