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Past Articles Library | Guide to Growing Dianthus

When one thinks of the Dianthus, the mind reflects either on pinks or carnations but believe it or not there is another plant that is in this genus and it is Sweet William. What separates each one of these plants in this genus is not flower color but height. Pinks are the shortest of the Dianthus genus and fit right into a rock garden due to their height. Carnations are the tallest and can grow up to 30 inches in height. They are also one of the oldest cut flowers. The flower that is between the pink and the carnation in height is Sweet William, which is a biennial or a short-lived perennial.

Since there is a vast difference in height between the three commonly known Dianthus species, this flower is a wonderful addition to any landscape design in USDA Plant Hardiness Zones 3 through 10. But…to maximize the beauty of this plant, it must be planted in well draining soil that is in full sun. While this genus is not forgiving when it comes to the soil requirement, this flower can tolerate some shade. Having said that though, the amount of shade this flower receives can be tricky and can cause some serious problems. When it comes to pinks, not enough sunlight will cause the mat of growth to rot at the crown since there is not enough sunlight by which to evaporate the water from the crown. On the other end of the height spectrum, carnations will grow spindly and topple over if they do not receive enough light. But even in the sunniest locations, the weight of the carnation bloom can cause the stem to bend. To protect the bloom, it is not uncommon to have to stake the carnation.

Propagation of Dianthus

When it comes to propagating this genus, it can be done by division or seed. Both techniques are easy and dividing is something that you will need to do every three to five years anyway, so let’s go ahead and learn how.

Dividing this genus can occur in the spring or fall. In my experience, it is better to divide this genus in the fall after it has stopped blooming. The reason for this is the fact that if you divide while the plant is still blooming, it may drop the blooms due to the stress. The same can be true if dividing in the spring when the plant may be delayed in setting blooms due to plant stress.

The first step of this process is to have a plan for your division. This means you know where your division is going to go. Once you have that, prepare the area by removing mulch and/or plant material and loosen the soil in the area 12 to 15 inches down. After that is done, incorporate two to four inches of well seasoned compost. At this point, the area is prepared for the hole. But…… will not know the size of the hole until the division has been completed.

When it comes to dividing this genus, you begin by moving aside any mulch. Next, using a shovel, begin to go around the diameter of the whole plant by pushing the shovel all the way down into the soil. The goal is to create a groove all the way around the plant. If you dug below the root mass, you should be able to begin to push down on the shovel’s handle while the shovel is in the groove and start lifting the plant out of the ground. If this is not happening, go back around the plant deeper until it does.

After the whole plant has been removed from the hole, take a knife and begin the cut the root mass into the size root mass you want. Keep in mind though that you not only want roots but also vegetation on top. Once you have the number of divisions you desire, replant them in holes that are the same depth as the root mass but twice the width.

Next, water the division in their new home so that the soil is evenly moist. Top the soil layer with a two inch layer of mulch.

Now, when it comes to growing your Dianthus there are two approaches. First, you can start them indoors 8 to 10 weeks prior to your local frost free date or you can directly seed into the garden space. If you choose this latter approach, you will really need to know your local area. While the seeds can take a mild frost, they do not do well in freezing temperatures. The ideal temperature range is 60 to 70 degrees Fahrenheit during the day. So if you are not sure about planting your seeds outdoors but still want to give it a shot, very early fall is a better approach. Planting during this time will give the seeds time to germinate and take root before the cold winds blow.

Regardless of when you decide to plant your seed, the key to success comes from keeping the soil evenly moist and only covering them with 1/8 of an inch of soil.

Once seeds have germinated, thin them so that there is 6 to 12 inches apart. This also applies to the process of division.

Caring for your Dianthus

To encourage your Dianthus to keep blooming, remove spent flowers as they appear but…….if you want additional plants, keep a few around so that the plant will reseed. There is an exception to this practice though and it comes from the fact that if you planted a short-lived perennial or biennial then the removal of the spent blooms will not encourage more blooms. In doing so, if you planted Sweet William, do not waste your time removing the dead blooms.

Landscaping with Dianthus

Yes, the wide range of flower colors and heights makes this genus a wonderful addition to any landscape design but just like anything else, it does not last forever. No, I am not talking about the plant itself but the bloom. To keep the color in your landscape design, do not simply depend on this genus to provide all the color through the season. Instead, combine it with other flowering plants that will provide that flush of color with the Dianthus is planning on blooming again.

Need some ideas?  Well, here are just a few. The key is to make sure the growing requirements are the same. The perennial geranium is one idea. This plant loves the sun and is a tough cookie when it comes to the landscape. While the perennial geranium name to fame is the length of its blooming season, the coralbells provide that unique foliage that adds texture and color to the space during those few times when nothing is blooming.

The last flowering plant is the iris. While this may appear as a strange companion plant, the fact is that this plant comes in several different heights. This prevents the issue of shading smaller Dianthus while at the same time providing a splash of color and texture.


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