Carnations (Dianthus caryophyllus) have been grown in home gardens for generations. They're also common florist flowers, used everywhere from restaurant tables to grooms' boutonnières. Carnations are not difficult flowers to grow in home gardens, but one common problem is the tendency of flower stems to break or flop over onto the ground. This problem can result from a variety of conditions and growing practices.
For best growth, carnations require highlight levels. Carnation plants grown in shade open up in the middle, causing the flower stems to break or fall over. Site your carnations where they'll receive at least 8 hours of direct sunlight daily.
Carnations need moist but well-drained soil. Soil that is too wet encourages softness or rot at the base of the stems, weakening them and causing the flowers to fall over. On the other hand, soil that's allowed to dry out stresses the plants and weakens the cell structure in the stems. Carnations don't need daily watering, but check their soil frequently, especially during hot or windy periods. If desired, mulch with sand or small stones, never with organic mulches such as straw or shredded bark.
Carnations are native to areas of southern Europe, where the soil is rocky and lean. Garden soil is rarely either, and that's a problem. Rich soil encourages rapid, lush growth, and the flowers outgrow the stem's ability to support the flower head. Don't fertilise your carnations unless you see signs of mineral deficiency, such as stunted growth or discoloured leaves. Always stake the flower stems, using bamboo stakes for each stem rather than rings around the plant.
The inherent top-heaviness of carnations makes them especially prone to damage from heavy winds, so if possible, site your plants where they're protected from prevailing winds. If it's not possible to site them out of the wind, stake them carefully to protect them from damage.
There are hundreds of carnation cultivars available. Tall varieties such as "Chabaud's Giant Improved" and "William Sim" were developed for the florist trade, which requires flowers with long stems. Greenhouse-grown carnations are tied to strings hanging from overhead wires, but that's hardly feasible in the home landscape. For home gardens, plant miniature or spray carnations, smaller varieties which grow 12 to 18 inches tall. The sturdy flowers are usually smaller, have shorter stems, and require little if any staking; the flowers are intensely fragrant. "Elegance" has white-edged, rose-pink flowers, "Exquisite" has purple flowers with white edges and "Juliet" grows to 12 inches with large, doubled scarlet-red flowers. The "Dwarf Fragrance Mixed" carnations are upright, compact plants with beautifully scented flowers.