Autumn tune-up for potted perennials

Sunset, Oct, 1992 by Emely Lincowski

Perennials in pots need very little care beyond watering, clipping spent blooms, and feeding for their first two years or so. But by the third year, they may look straggly and crowded.

Fall, after bloom is through, is a good time to divide them (in cold-winter climates, wait until spring). The task takes 45 minutes or so; it's simple if you follow the steps listed here.

1. TRIM PLANTS

Using sharp hand pruners, cut back plants. How much you cut will depend on the plant. Tall, semishrubby ones like Alyogyne, Anisodontea, and Salvia can be cut back to 6 to 12 inches. Mounding and trailing types--like blue ground morning glory, cranesbill, Diascia, lavender, Mexican daisy, santolina, Verbena peruviana, and yarrow--can be trimmed to tight mounds about 2 to 4 inches tall.

2. REMOVE PLANTS

If roots are dense and the rootball is hard, you may need to use a shovel to loosen plants from the pot; rock the shovel slowly back and forth between plants and around the inside of the pot. A large old knife also comes in handy to scrape around the inside edge of the pot. Tip the pot on its side, then slide the rootball out.

3. DIVIDE PLANTS

Using a sharp shovel or knife, make clean cuts through the rootball between and under plants; also trim roots. For plants that spread and form thick clumps, like lamb's ears, black-eyed Susan, and yarrow, you may need to slice through the crown of the plant to make divisions. Keep vigorous outer growth; discard center portions or any pieces that appear shriveled or diseased. Rub some of the old soil off the rootball.

4. REPLANT CONTAINER

Fill the container with fresh potting soil. If the plants are healthy, mix fresh soil and compost with part of the old soil (if you reuse old soil, break it up). Mix a slow-release fertilizer into the soil, or use a balanced formula such as 10-10-10.

Replant divisions. Be sure to set plant crowns at the same level as before; otherwise, they can rot in cool, wet weather. Firm soil by gently pressing it with your hand. Water thoroughly and deeply.

TO RENOVATE YOUNGER PLANTINGS ...

Plants less than 2 years old, or ones you divided last year, can benefit from a lighter tune-up this month (in cold-winter climates, wait until spring).

Cut plants back as described above. Then with a screwdriver, poke three 1-inch holes about 6 to 8 inches deep in soil (keep holes about 2 inches away from plant crowns). Drop about a teaspoon of complete fertilizer such as 10-10-10 into each hole and cover with soil. Lightly scratch the soil surface and add about an inch of compost or topsoil.