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How to Divide Garden Phlox

Eastern Swallowtail on Garden Phlox
Eastern Swallowtail on Garden Phlox
Don Delaney: Flickr

Garden phlox (Phlox paniculata) bloom in midsummer and release a heady sweet fragrance that engulfs you on warm summer evenings. Traditional garden phlox are either magenta or white and can be found around old homesteads in the country. New hybrids offer the gardener a wide range of colors, from pink and lavender to salmon and bicolors. Phlox blossoms are made up of a cluster of tiny five-petaled flowers that give them impression of one large bloom.

Phlox thrive in full sun in moist, well-drained soil and reach heights of 2 to 4 feet depending on the variety. Most varieties are hardy in US Department of Agriculture plant hardiness zones 3 through 8. Because phlox need good air circulation to prevent problems with disease, the University of Illinois Extension recommends dividing them whenever the clump becomes crowded - typically every 3 to 4 years.

When to Divide Phlox

The best time of the year for dividing phlox is early spring, but they can also be divided in late summer and fall. Watch your phlox for new growth in the spring and divide them with the new growth is a few inches tall. This makes division easier as you can see the number of shoots on each root section.

Preparation

Water your phlox thoroughly the evening before you intend to divide them. This gives the plants the moisture they need to combat the stress of being moved and loosens the soil to make digging easier. Prepare the soil in the new location by loosening it to a depth of 8 inches and adding plenty of organic matter.

Let's Get Digging

Use a garden shovel or fork to dig up your phlox. Dig deeply around the base of the section you wish to divide and slide the shovel under the roots. Lift the clump free of the soil and shake gently to remove excess soil from the roots.

Separating the Phlox

Fill a 5 gallon bucket with lukewarm water and soak the root portion of your phlox in the water to loosen the soil around the roots. You can also use the hose to wash away the soil. This exposes the massive root connecting clusters of phlox and makes cutting the root easier. Use a sharp knife to cut the roots into sections that have at least 2 or 3 new shoots. Work the smaller roots free of the tangled mass to expose them to the new soil.

Transplanting Phlox

Dig holes for your phlox in prepared soil so the holes are slightly larger than the root system. Pour 1 to 2 quarts of water into the hole and allow it to drain. Position the phlox plants into the holes so that the roots are spread out over the soil. Fill in around the roots with fresh soil and firm down gently with your hands. Water the newly planted phlox to moisten the soil to the root level and keep it moist for the first few weeks until your phlox are established.