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How to Grow Phlox Flowers

Updated on June 24, 2014


Phlox is a beautiful, small flower plant usually used as edging for gardens or yard landscaping, as well as ground cover for targeted areas.

For those of you reading this who think phlox is really easy to grow, that's a misconception, as the process of sowing seeds is a little more difficult and unpredictable that it may seem.

Now once phlox has taken root and is growing well, at that time they are relatively easy to grow, and take just a little bit of maintenance to keep them thriving.

Over the last several years some breakthroughs have been made in phlox varieties, and now there are some that can grow taller than their predecessors, taking on a new look and feel.

Since many other flowers can fill that particular niche, phlox will remain one of the favorites of gardeners and landscapers looking for that great color residing close to the ground.

Growing Phlox from Seed

Phlox can be propagated from seed, along with several other ways. First we'll look at growing phlox from seed and what we can do to boost the germination rate of the temperamental seed.

Usually the biggest challenges for those propagating phlox through the sowing of seeds is with perennial phlox, although annuals, to a lesser degree, aren't hurt by a little help.

Sowing Perennial Phlox Seed

A seed study was performed by John's Hopkins University concerning the native longleaf phlox (Phlox longifolia L. [Polemoniaceae]), in order to see if they could boost the germination success of the seed.

Bypassing the variety of experiments which didn't do as well as the most successful, let's look at what helped the most.

Seeds of the phlox received a cold treatment of 45 °F (7 °C), whereby they were placed in a Petri dish in the dark on filter paper.

Within a period of 7 to 10 days, those seeds receiving this particular cold treatment germinated at a 90 percent rate; a very high percentage for perennial phlox seed.

The conclusion was the process, which is called stratification, would vastly improve the results for gardeners or nurseries propagating the seed.

Preparing Other Phlox Seed Varieties

Gardeners trying a revised or similar process with other phlox seed varieties have reported stronger germination rates as well. They've recommended placing the seeds on slightly moist peat moss or sand and putting them in plastic bag while being refrigerated for about a month.

After this, go through the usual process of seed germination in flats or pots. For phlox it should take from 7 to 10 days to germinate once the stratification process has been completed.

All of this is done to increase the percentage of seeds being germinated, not to quicken the germination time, which will remain the same.

Light isn't needed for phlox seeds to germinate, and in fact respond to the dark for best success.

Transplanting Phlox Seedlings

If you're growing phlox seedlings to insert into the soil outside, there are a couple of steps to take.

First, start the seeds about six to eight weeks before the average final frost date for your zone.

To successfully manage the seedlings after germination, keep the soil moist until the racicle breaks through the mix. From there, gradually reduce the amount of moisture, but be careful not to allow the plant to wilt in the early stages.

When the actual leaves appear, you can fertilize it with about 100 to 150 ppm of nitrogen in nitrate form.

When you're ready to transplant the seedlings, dig a hole only enough so the top of the root ball is level with the surface of the soil. Fill it in and press or tap the soil to firm it up. Give it a good dose of water and it should be enough to start it on its journey.

Planting Phlox Seed Outdoors

After the stratification period, if you've timed it right and it's your goal, at that time you can plant the prepared seeds directly into the ground, covering them with about 1/8" of soil or mix. Give them a good dose of water at this point to help them along.

As for placement, phlox love the sun, so keep that in mind where you're placing them in the ground, or if you're sowing them in in containers to place or hang.

Having said that, there are some varieties that respond better to a little more shade, so be sure to check your varieties to be sure on the best place to set them out in pots or in the ground.

When sowing directly into the ground, space them at intervals of approximately 8" to 10" apart. They don't mind some crowding, but putting them too close can result in them competing for nutrients and could make them more susceptible to mildew or fungus.

Be sure the last frost date is safely gone before you sow your phlox seed. A minimum outdoor temperature should be in the lower 50s and up for best results for phlox.

Garden Tips : How to Transplant Phlox Flowers

Other Ways to Propagate Phlox

There are several ways to propagate phlox besides using seeds. You can divide them, take cuttings from stems, or take cuttings from roots.

Dividing Phlox

When using the division of clumps as the choice of propagating phlox, it should be done every third year, as the plant has a history of weakening at the center after living for that long. This is especially true with the taller phlox varieties.

For me, I have found it rather easy to just pull the phlox grouping apart according to the desired size and place them where I want. Some may recommend being a little more careful, but it has successfully worked for me.

Those propagating creeping phlox recommend dividing right after they bloom in the spring.

Stem Cuttings

Stem cuttings are another good way to grow phlox. The most important thing here is to make your cuttings before a lot of growth is on them, or when they are slowing down.

The best times to do that are in the early part of spring or in the latter part of fall.

Root Cuttings

The final way to propagate phlox is via root cuttings. With root cuttings you cut approximately a 2" piece from the root and sow them in flats. From there you manage them in a similar fashion you would seeds.

Best practices for this is to also do it in early spring or fall.

Gardening Tips : How to Grow Annual Phlox (Phlox Drummondii)

Maintaining Phlox

Phlox are rather easy to care for, but there are some things to watch for or you can do to get the most enjoyment out of them and to make them perform the best for you.

Most of the things you do for other flowers to make them do well are the same things you will do for phlox.

Once the warm season gets under way, you of course must be aware of how much rain you get in order to be sure your phlox are getting enough water.

You should visually check them if they aren't getting about an inch of rain on a weekly basis. They don't need a lot of water, but do keep them slightly moist during dry periods.

Deadheading and Pinching Off Stems

To get fuller and stronger blooming plants, phlox responds well to pinching off the stems to promote bushier plants.

Deadheading phlox will not only promote better blooming, but will also extend the blooming period throughout the entire summer. This also makes your phlox area look neat and clean.

Disease and Insect Management

Phlox is resistant to disease and insects, but they occasionally are challenged by mildew, especially with taller varieties, or if your phlox start to get too crunched together and they don't dry well.

The treatment is to simply thin out your phlox clumps to the more healthy stems.

Planting them further apart in the first place is also a good preventative, although over time they'll naturally crowd together; the reason they need to be thinned once in a while.

Insect Management

Most of the problems I'm aware if there are insect problems with phlox is in regard to nematodes.

That is easily taken care of by insecticides that eradicate or significantly reduce the population.

Closing Down for the Winter

When the plants experience their first heavy frost, at that time you can trim phlox stems to about an inch or two above the soil line in preparation for next spring.

There's nothing more to do than that.

Phlox Benefits and Uses

The variety and uniqueness of phlox makes them ideal for all sorts of landscaping needs.

Not only can you plant them in bunches to give that appearance of blanketed color, but you can insert them in all sorts of nooks and crannies to fill in holes in parts of your garden or yard that need it.

These fantastic little plants can also be successfully sown on hills and by rocks or stumps to create a wonderful effect that can be experienced on an annual basis.

Phlox also attracts butterflies and are also known to be the target of hummingbirds at times.

As you can see, this versatile flower is a terrific addition to any garden and can easily be propagated year after year once you get them successfully planted. It doesn't get much better than that.


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    • RTalloni profile image

      RTalloni 5 years ago from the short journey

      Phlox are indeed fantastic plants. It's interesting to read about the different propagation methods but I think I'll stick with division. :) Thanks for more info on taking care of phlox!