Gadenin日本語Get the appThe conditions the plant is actually asking for
A carnation is a cool grower with a heat tolerance most people overestimate. It wants full sun, meaning six hours of direct light and preferably eight, but it wants that light without a hot, still, humid pocket of air around the foliage. The best plants are grown where the sun is strong and the air keeps moving. In a sheltered corner against a warm wall you will get soft stems, weak color and mildew, even though the light meter says the position is fine.
Soil matters almost as much. Carnations belong on gritty, free-draining ground on the alkaline side of neutral, and they sulk on heavy soil that stays wet. In containers, a loam-based mix with a third by volume of grit added beats a peat-type compost on its own, which holds too much water around the collar. Whatever the medium, the crown of the plant sits at the surface and never gets buried.
Temperature steadiness is the condition that separates good blooms from disappointing ones, and it is the one gardeners think about least. Nights around 50 to 55F (10 to 13C) with days in the 60s to low 70s F (16 to 23C) produce firm, well-filled flowers. Repeated swings between a cold night and a hot day, which is what a cold frame or a small greenhouse delivers unless it is vented early, is what makes the calyx split and the flower fall apart.
| Condition | What to aim for | What goes wrong outside that |
|---|---|---|
| Light | Six to eight hours of direct sun, with air movement | Stems stretch, color pales, mildew starts on the lower leaves |
| Night temperature | 50 to 55F (10 to 13C) through the flowering season | Warm nights give soft, thin-petalled flowers that open too fast |
| Temperature swing | Under about 20F (11C) between night and day | The calyx splits and the petals spill out on one side |
| Soil | Gritty, free-draining, neutral to slightly alkaline | Wet acid soil rots the collar and the plant dies from the base |
| Feeding | Light, regular, potassium-leaning once buds show | High nitrogen gives lush foliage, weak joints and split calyces |
Disbudding: one bud per stem
Left alone, a carnation stem produces a terminal bud and then four to six smaller buds in the leaf joints below it. The plant divides its resources between all of them and you get a spray of undersized, thin flowers that open unevenly over two weeks. The single large bloom people expect from a carnation is not a matter of variety or of feeding. It is the result of removing every side bud so that one bud receives everything the stem can supply.
Do it early, while the side buds are the size of a grain of rice and still soft. At that stage they rub out cleanly with a sideways push of the thumb and the stem is not marked. Wait until they are pea-sized and you have to cut them, which leaves a wound at a leaf joint, and the joint is exactly where the stem is weakest. Go over the plants every four or five days once buds begin to form, because they appear in sequence rather than all at once.
Work down the stem from the top. Keep the terminal bud, which is the largest and the furthest advanced, and take out everything below it. If the terminal bud has been damaged by a slug or has already split, take that one out instead and promote the strongest side bud, then remove the rest. The result is a straight stem carrying one flower, which is what makes the difference between a carnation that looks like a florist's and one that looks like a weed.
- Start when the first side bud is visible As soon as you can see a small bud in a leaf joint below the top bud, the plant has begun branching. That is the moment to start, not when the buds are obvious from across the garden.
- Rub, do not cut Push the small bud sideways with your thumb and it comes away at the joint with no wound. Cutting a larger bud leaves a stub that can rot and weakens the joint below the flower.
- Keep the top bud only Remove every bud below the terminal one on each flowering stem. If the top bud is damaged, promote the next strongest and take out all the others instead.
- Repeat every few days New side buds keep appearing for two or three weeks. One pass is never enough, and a bud missed early is a bud you have to cut later.
Support every stem, because the joints snap
Carnation stems are brittle at the nodes. They are not flexible the way a chrysanthemum stem is, and they do not bend and recover after wind or rain. They break clean at a leaf joint, usually about two thirds of the way up, and a broken stem is finished for the season because the plant will not push a replacement flower from below in time. The damage nearly always happens in the first strong wind after the buds have gained weight.
General support does not work well here. A single cane in the middle of the clump or a hoop around the outside leaves each stem free to whip and snap. What works is individual support: a thin cane beside each flowering stem, tied loosely in two places, the lower tie at about a third of the height and the upper one just below the bud. A soft tie in a figure of eight lets the stem move a little without sawing on the cane.
Where there are too many stems for individual canes, use a grid instead. Stretch large-mesh netting horizontally over the bed about a foot (30 cm) above the soil before the stems elongate, and let them grow up through the squares, with a second layer a foot higher again. Both layers have to be in place while the stems are short, because you cannot thread a grown stem through a mesh without breaking it.
Put supports in before you need them. Once a stem has reached full height with a heavy bud on top, the act of tying it in is itself enough to snap the joint. If you find yourself bending a stem to bring it to a cane, move the cane instead.
Water and feed on the dry side
Water at the base and never over the top. Overhead watering wets the foliage, and wet carnation foliage in still air is how both rust and powdery mildew get started. It also splashes soil onto the lower leaves, which is where stem rot usually begins. A can with the rose taken off, aimed at the soil around the collar, is the correct tool. Do it in the morning so that anything you do splash has the day to dry.
Let the surface dry between waterings. Carnations tolerate short dry spells far better than they tolerate constantly damp roots, and a plant that has been kept a little dry has firmer stems and better color. In containers, lift the pot: it should feel noticeably light before you water again. In open ground on gritty soil, established plants need water only in a genuine dry spell, though newly planted stock needs regular water until it has taken hold.
Feed lightly and often rather than heavily and rarely. A balanced liquid feed at half strength every two weeks through active growth is enough, and once flower buds are visible, switch to something with more potassium than nitrogen. High nitrogen is actively harmful at this stage: it produces soft, thick-walled growth, weak leaf joints, and calyces that are far more likely to split. If the foliage is dark green and lush and the stems flop, you are overfeeding.
What to write down
Keep four things per plant: where it is, the date you first disbudded it, the date the first flower opened, and the number of stems it carried. The gap between the first disbudding pass and the first open flower is the figure that lets you time the next season, and it varies far more with your own site than with any published table.
Add a line whenever a calyx splits, with the weather of the previous few days beside it. After two seasons that record will show you plainly whether your splits follow cold nights, sudden heat, heavy feeding or a soaking after a dry spell, and that is the only way to work out which one is happening in your own garden rather than in general.