Annual carnations, known botanically as the species Dianthus, are hardy or half-hardy annuals that can survive light winter frosts. They are sown by seed or planted in the fall for spring and early summer flowering. They fade or die back when summer heat surges but often resurrect in the fall when temperatures cool again. Moist soil, gentle slow-release fertilizer and a fall application of mulch will work together to successfully overwinter annual carnations in climates where temperatures remain above freezing.
Plant annual carnations by seed or mature plant at least six weeks before the first frost is anticipated so the roots have time to develop. Pinch away any flower buds on the mature plants in order to redirect the plant energies back down to the roots. This will result in stronger branches and larger blooms come spring.
Water your annual carnation plants deeply in the early and mid-fall to drench the roots and surrounding soil. Deep watering applied before frost will help the plants fight off winter drought stress. Water in winter when rain has not been plentiful and the soil feels dry to the touch. Water in the morning on a sunny day to help the soil absorb the moisture easily.
Fertilize your annual carnations in the mid-summer with a 10-10-10 slow-release granular fertilizer. Apply according to label dosing directions, but do not exceed 1 lb. of fertilizer over 100 square feet of soil surface. Nestle the grains into the surface soil gently and water in well.
Apply 3 inches of organic mulch in the fall before the first hard frost hits. Use pine bark, straw or other lightweight material around the plants to insulate the plant roots, hold moisture and keep weeds out.