Dianthus is a genus of 300 species of flowering plants. Here at Bob's we grow dianthus that we sell in bedding flats, and we also sell perennial types of dianthus that come back every year. Overall dianthus is a pretty hardy plant. Even somebody with a brown thumb would have a hard time killing it. Nevertheless, here are some tips to help you get the most out of your dianthus.
First off, there is sometimes a bit of confusion about our dianthus in bedding flats. We sell it as an annual, but many customers say that it is a perennial. The confusion is simply created by our geographic location. These dianthus plants are biennial, or short-lived perennials, but because of our unpredictable winters they may either be killed in a hard freeze or survive through a mild winter. That's why we sell them as an "annual". Basically we only sell plants as perennials if we know it has a near 100% chance of surviving our winters. With bedding dianthus it is more like a 25% chance.
Select a site with full sun and well-drained soil, preferably with neutral to alkaline soil pH. Dianthus won't tolerate wet soils, especially in winter.
Plant in spring or fall, spacing plants 6 to 12 inches apart, depending on the type. Prepare the garden bed by using a garden fork or tiller to loosen soil to a depth of 12 to 15 inches, then mix in a 2- to 4-inch layer of compost. Dig a hole twice the diameter of the plant's container. Carefully remove the plant from its pot and place it in the hole so the top of the root ball is level with the soil surface. Carefully fill in around the root ball and firm the soil gently. Water thoroughly.
Apply a thin layer of compost each spring, followed by a 2-inch layer of mulch to retain moisture and control weeds. Water plants during the summer if rainfall is less than 1 inch per week. Stake tall varieties to keep them upright. Remove spent blooms on tall varieties, or shear back mounding plants after bloom to encourage rebloom. After the first killing frost, cut stems back to an inch or two above soil line. Divide plants every 3 to 4 years as new growth begins in the spring, lifting plants and dividing them into clumps.