Dianthus is native to southern and eastern Europe and Asia, where winters are cold and summers hot, have thrived for centuries in dry, rocky areas of the Mediterranean countries and in mountain meadows as far east as Japan and Taiwan. The dianthus we plant today, descendants of these ancestral plants, enjoy similar conditions. They're easy to cultivate in varying conditions, provided summers are not too warm and humid and the plants' need for sharp drainage is met.
The different groups of Dianthus, whether they are perennial pinks, border carnations, sweet William or the annual varieties, all crave summer warmth, sun and light. Choose a site where they will not be hidden in shade beneath overhanging trees or tucked in behind bushy shrubs. Evening dampness can encourage fungal disease, so keep them away from fences and other structures that restrict air movement. With plenty of space they remain healthier plants, so make sure they will not be overcrowded by fast-spreading perennials planted too close. Most dianthus are front-of-the-border plants that want to flaunt their bright colors or their delicate markings for everyone to see. And one of the joys of pinks is their delicious perfume. Plant them where it's easy to bend down and savor their fragrance.
Soils vary considerably in their composition, from extreme acidity to extreme alkalinity, the relative alkalinity or acidity being expressed as the pH value. A pH of 7 is neutral, the level where dianthus are happy, though they will tolerate some variation on either side.
Dianthus like the free-draining, well-aerated qualities of gravelly or rocky soil, their natural habitat, so it makes sense to provide conditions that simulate this as closely as is reasonable. They are not notably fussy plants but they don't like wet feet and will quickly die in heavy, anaerobic clay conditions where drainage is poor. But, if this is the kind of soil you are blessed with, don't despair. It is possible to change it. Coarse sand, dolomite and gypsum will help to open up clay; adding quantities of humus is also effective. Rotted leaves, mushroom compost (which contains lime and is therefore suitable for dianthus), composted grass clippings, pine needles and rotted manure are all suitable. Stable horse manure-if you can get it-works well in heavy soils because of its high straw content. If you live close to the ocean where it's easy to access seaweed, you will find it beneficial.
Sandy soil, like clay soil, lacks humus, though the results it produces are different. While dianthus like the perfect drainage offered by sandy soils, plant nutrients are quickly leached out and instead of holding moisture-with the attendant risk of drowning plants-this kind of soil dries out so quickly that the plants run the risk of dying from thirst. Incorporating humus-forming materials will bulk up the soil and improve its ability to retain moisture and nutrients.
Creating raised beds is an excellent way to improve drainage-and "raised" does not necessarily mean to a great height. Provide an edging just two bricks high, top up the bed behind it with soil that includes plenty of humus and the drainage will be instantly improved.
The prolific flowering habit of some modern dianthus, and particularly the annual dianthus, will be aided and abetted by soil enriched with fertilizers before planting time. Well-rotted manure, blood meal and mushroom compost all supply valuable nutrients. A balanced manufactured fertilizer with an NPK in equal ratios is also suitable (10-10-10, for example, where N = nitrogen, P = phosphate, K = potassium). Information on its use is printed on the packaging and usually gives details about the quantities needed for varying plant families.
When your dianthus are coming into bloom, a liquid feed high in potassium helps to maintain strong stems and buds and increase the number of flowers. It also enhances their color. Plants in the Dianthus family, however, do not require rich soil and too much nitrogen will encourage soft foliage growth at the expense of flowers.
Controlled-release fertilizers help to take the guesswork out of feeding plants. Different varieties are available and the time over which they release their chemicals also differs, ranging from two or three months to two years. These fertilizers are especially practical for container planting and are often already an ingredient in commercial soil mixes. Useful in the garden too, they can be added to the soil when a patch is being prepared for the planting of any members of the carnation family. In their second and third years, plants will appreciate a supplementary liquid feed when new growth is starting.
For gardeners who prefer an organic approach, liquid fertilizer (or manure tea) made by diluting manure in sufficient water to produce a thin, weak brown solution is effective and easy to use, though care must be taken to dilute sheep and fowl manure sufficiently as they can be too rich. Water-soluble powder fertilizers containing seaweed and other beneficial, natural fertilizers are also widely available now. To avoid any risk of burning the roots, fertilizers should be added only when the soil or potting mix is already moist.
Garden pinks are described as perennial, but have a relatively short life as productive garden plants. After two or three seasons they tend to lose their vigor and flower less prolifically. It's a good idea to take cuttings and replace your plants approximately every three years. New ones can be grown from seed, but remember that named varieties will not come true to type.
Pinks are hardy. Many will survive where winter temperatures sink as low as -40°F, though losses may occur when there is a sudden drop in temperature before an expected snowfall. On the other hand, they do not like excessive warmth and humidity. Frosts during severe winters can dislodge young plants and you may need to firm them back into the soil. Check regularly to ensure that they remain well anchored. During a long, dry summer, give your dianthus a generous watering from time to time preferably in the morning to avoid a humid atmosphere after nightfall. Dianthus can, however, withstand extended dry periods and will revive quickly once it rains.
Mulching helps to retain moisture in the soil, but these plants of dry rocky places like freely circulating air. They don't appreciate being cosseted with a blanket of moisture-holding material bulked up right around their throats. If you must mulch, use a layer of scoria or pumice around your dianthus. The modern varieties of repeat-flowering pinks need to be pinched back when still young plants, to produce more flowering shoots. Repeat-blooming varieties also need deadheading-removing spent blooms-after each flush to promote further flowering. Remove the stems as well as the heads.
When the plant has eight or nine pairs of leaves, it is time for the first pinching. This encourages the growth of side shoots and therefore more flowering stems. Snap off the growing tip, leaving five or six pairs of leaves. Approximately two weeks later, new side shoots should have appeared, sprouting from the leaf axils.
About this time, too, the roots should have penetrated the mix to the outsides of the pot and will perhaps show signs of emerging through the bottom holes. This means the young plants are ready to move into larger pots. Transfer them into 6-7 in (15-18 cm) pots and insert a stake alongside each plant for support when it is flowering.
Many growers pinch their plants a second time when the new shoots are long enough to have the top two or three sets of leaves nipped out, once again leaving five or six pairs. Flowers usually appear between five and six months after pinching, so the timing of this operation will determine the flowering sequence of the plants, an important consideration for commercial growers. Shoots that are left unpinched flower earlier, but less abundantly.
Disbudding is a technique used to increase the size of flowers. Perpetual-flowering carnations are admired for their large blooms; so they are usually disbudded. This reduces the number of flowers per stem but ensures that the one bloom remaining will be as big as possible. To disbud, simply remove the thin side stalks every few days as they develop, leaving only the crown bud to develop on each flowering stem.
If it is spray carnations that you are growing, however, then the reverse is true. Nip out the crown bud only, leaving other stalks intact, to encourage multiple blooms on the stem.
Plants potted in soil are less likely to drain as evenly as those grown in soil-less compounds, such as mixtures of peat, sand, and perlite, for example. In summer it is important to prevent the plants from drying out completely. The surface of the mix is an indication: if it is dry, insert your finger a few inches (several centimeters) into the compost to test the moisture below the surface. If it feels damp, watering can wait. If it is dry, water your plant. Small plants can be gently knocked out of the pot to check for moisture around the root area, but take care not to damage the roots. Once you decide to water, it is important that it seeps right through the mix and does not merely wet the visible surface.
Water early in the day to allow foliage to dry off and avoid scorching by sun, and to avoid unnecessary humidity at night. As summer wanes and the weather becomes cooler, plants require less watering and by mid-winter, established plants prefer to be kept relatively dry.
Provided the original potting mix was enriched with fertilizer, potted plants will not need further feeding until the buds start to appear. From then until late autumn, feeding "little and often" works well. Dilute a balanced fertilizer in water, according to the instructions on the package, and use this mixture at watering time. If the soil has dried out, however, wet it thoroughly before adding any fertilizer, for it may burn the roots when applied directly to dry plants. Give plants growing in an unheated greenhouse in winter one high-potash feed in mid-fall, or you can sprinkle a controlled-release fertilizer around the root area. Plants overwintering in warmth should also receive a monthly, high-potassium feed.
When spring comes, any strongly growing plants will need to be repotted into bigger containers, 8 or 9 in (20 or 23 cm). Start feeding again at biweekly intervals, once they have had a few weeks to settle into their new pots. By early summer this can be increased to weekly feeding. Heating in many areas can be discontinued in late spring when daylight has increased and night temperatures have risen to above 50°F.