How to Propagate Phlox: The Best Times and Methods

Phlox are a common sight in gardens, known for their abundant and often fragrant flowers that create long-lasting displays of color. For gardeners looking to increase their stock of these plants, propagation offers a straightforward way to create new plants from an existing one. This process allows you to expand plantings, rejuvenate older clumps, or share favorite varieties with others.

When to Propagate Phlox

The correct time to propagate phlox depends on the chosen method, as each technique is aligned with a specific stage of the plant’s annual growth cycle. Attempting propagation outside these windows can reduce the chances of success.

Division is best performed in either early spring, just as new growth begins to appear, or in the fall. If dividing in autumn, it is recommended to do so four to six weeks before the first expected frost, after the plant has finished its flowering period. Stem cuttings are ideally taken in late spring or early summer. For root cuttings, the optimal time is during the plant’s dormancy in late fall or early winter, before new shoots emerge in the spring.

How to Propagate Phlox

Propagation by Division

Division is a method for expanding clump-forming phlox varieties. The process begins by carefully lifting the entire plant clump from the ground with a spade or garden fork, retaining as much of the root system as possible. Once unearthed, the clump can be separated into smaller sections. For dense clumps, a sharp spade or garden knife may be needed to cut through the root mass, while looser clumps can sometimes be gently pulled apart by hand.

Each new section must have a healthy portion of the root system and at least a few shoots or growth points. Signs that a plant may benefit from division include reduced flower production or a sparse center in the clump. After separating the divisions, inspect them for any damaged portions and trim them away. Replant the new divisions promptly at the same depth they were previously growing.

Propagation by Stem Cuttings

Using stem cuttings is another effective way to propagate many types of phlox. Select healthy, vigorous stems that are not currently producing flowers. Take a cutting that is approximately four to six inches long, making a clean cut just below a leaf node, which is the point on the stem where leaves emerge. After taking the cutting, carefully remove the leaves from the lower half of the stem to expose the nodes.

While not mandatory, dipping the cut end of the stem into a rooting hormone can encourage faster root development. Plant the prepared cutting into a small pot filled with a sterile, well-draining potting medium. To maintain moisture and create a humid environment, you can cover the pot with a plastic bag. Place the container in a location that receives bright, indirect sunlight, and keep the soil consistently moist but not waterlogged. New growth typically appears within four to six weeks.

Propagation by Root Cuttings

Propagation by root cuttings is a practical method for some phlox varieties and is best done when the plant is dormant in the winter. Carefully excavate the soil around the base of a mature plant to expose some of the thicker, fleshier roots. Select a few healthy roots that are about the thickness of a pencil and, using a clean, sharp tool, remove them from the plant as close to the base of the stem as possible.

Cut these harvested roots into segments that are about two to three inches long. To help remember the correct orientation, it can be useful to make a straight cut on the end closest to the plant’s crown and an angled cut on the end farther away. Lay the root segments horizontally in a tray or pot filled with a moist potting mix and cover them lightly with more mix. Place the tray in a protected environment, like a cold frame, where new plants will develop by midsummer.

Caring for New Phlox Plants

Divisions should be watered thoroughly after being replanted to settle the soil around the roots. They may exhibit some wilting, a sign of transplant shock, but consistent moisture will help them recover. The soil for all new phlox should remain damp but not soggy to support new root and shoot growth.

Cuttings require a humid environment to form roots, which can be created by covering the pot with a plastic bag. Once cuttings have rooted and show new growth, they need to be gradually acclimated to outdoor conditions, a process known as hardening off, before being planted in the garden.

Newly propagated plants also require specific light conditions. Cuttings should be kept in bright, indirect light to prevent scorching while they root. Divisions can be planted in their final sunny location, but protection from intense sun and wind may be beneficial for the first couple of weeks.