How Far Should I Cut Tall Phlox Down in Winter?

Standard Procedures

• Hardy perennials like phlox die back to the ground with the first hard frost and regrow the following spring within the growing zone. Cut out and get rid of the old growth in winter when tall phlox dies back with the first hard winter freeze. Use a pair of sharp shears or garden scissors to cut through the stalks 1 to 2 inches above the soil line. Clear away dead leaves and other plant material as you go.

Disease Prevention

• Tall phlox commonly suffers from powdery mildew. While powdery mildew can appear anytime during the year, leaving old foliage through a wet winter creates a prime opportunity for the disease to develop and spread. If you notice white circular spots growing on tall phlox leaves and stalks in fall or early winter, cut it back even if the first hard frost hasn't yet killed the plant. Put dead leaves and stalks into a garbage bag to keep the disease from spreading to other plants.

Sanitize Tools

• Whether the tall phlox you're cutting back shows signs of disease or not, sanitize your pruning tools between each plant and pruning project. You can use bleach or strong alcohol, like rubbing alcohol, diluted in water. The University of Florida recommends either mixing one part bleach with three parts water or using half alcohol and half water. Leave each tool in the bucket with sanitizer for at least five minutes.

Pinching and Deadheading

• Besides winter cleanup, tall phlox benefits from pinching and deadheading during the gardening season. Using your fingernails, snip or pinch off the top set of leaves on each stalk right above the lower set of leaves. Pinch back tall phlox in late spring or early summer. After the summer flowers start to fade, encourage more flowers into the fall by deadheading tall phlox. To deadhead tall phlox, snip each flower head from the stalk.