Gadenin日本語Get the appSow into cool soil, earlier than feels comfortable
Stock germinates best at 55 to 65F (13 to 18C) and germination falls away sharply above 70F (21C). Sown into soil that is already warm, a proportion of the seed goes dormant rather than dying, so you get a thin, ragged stand and blame the seed. The practical rule is to sow while the ground still feels cold to the back of your hand, not once it feels pleasant.
That timing has a second reason behind it, which matters more than germination. Stock needs a run of cool weather after it has made a few true leaves before it will set flower buds properly, and it stops flowering when nights stay warm. Seed sown late spends its whole seedling life in warmth, misses the cold spell, and grows into a leafy plant that never blooms. Sowing early is not fussiness, it is the whole mechanism.
Where winters are mild, with lows staying above roughly 20F (minus 7C), sow in late summer or early autumn and overwinter small plants for a long, heavy flush in spring. Where winters are harder, sow under cover in late winter and plant out as soon as the ground is workable, several weeks before the last frost date. Young stock takes a light frost without damage; it is the flowering plant that is tender.
| Sowing time | Where it suits | How it is grown on | What you get |
|---|---|---|---|
| Late summer or early autumn | Mild winters, lows above 20F (-7C) | Overwinter outdoors or in a cold frame | Tallest plants, heaviest scent, earliest flush |
| Late winter under cover | Cold winters | Cool bright bench at 50 to 60F (10 to 16C) | Good spikes, flowering through late spring |
| Earliest spring, direct | Anywhere the soil is workable early | Thin in place, no transplanting | Sturdy plants, slightly later, no root check |
| Late spring | Nowhere, if you want flowers | Grows fast in warmth | Leaves, few or no spikes, quick collapse in heat |
Depth, light and the first fortnight
The seed is small and needs light to germinate reliably, so it is barely covered. Sow on the surface of a firmed, moist compost and sift the thinnest dusting of vermiculite or fine compost over the top, no more than an eighth of an inch (3 mm). Seed buried half an inch deep will sit there and rot. Expect emergence in seven to fourteen days at the right temperature.
Keep the surface damp but never sodden. Stock seedlings damp off readily, and the combination of warmth, still air and a wet surface is what kills them. Water from below where you can, give the seedlings moving air as soon as they are up, and drop the temperature rather than raising it once the first pair of leaves shows.
- Fill and firm Use a free draining seed-starting mix with added grit or perlite. Fill trays or cells, tap down, and firm lightly so the surface is level. An uneven surface leaves seed sitting in puddles.
- Sow thinly on the surface Space the seed about half an inch (1 cm) apart, or two seeds per cell if you are using modules. Crowded seedlings stretch and are much harder to sort into singles and doubles later.
- Dust, do not bury Cover with a sifting of vermiculite just thick enough to hide the seed. Water in with a fine rose or by standing the tray in shallow water until the surface darkens.
- Hold at 55 to 65F (13 to 18C) A bright windowsill in an unheated room is closer to right than a propagator. Heat above 70F (21C) both suppresses germination and produces weak, drawn seedlings.
- Move to full light immediately As soon as the first seedlings break the surface, give them the brightest, coolest spot you have. A day of dim warmth at this stage stretches the stems permanently.
Telling the doubles from the singles at two leaves
Strains sold to produce double flowers do not produce them on every plant. Roughly half the seedlings carry the genetics for doubles and half will open as singles, and the doubles are the ones worth the space, because they hold longer, sit heavier on the spike and carry far more scent. The useful trick is that the two kinds look different long before they flower, so you can throw away half the tray and grow only what you want.
The difference shows in the seed leaves and the first true leaves. Double seedlings are paler, a light yellow-green rather than a deep gray-green, and their leaves are noticeably larger and rounder for the same age. Singles are darker, smaller and more upright. The gap is easiest to see when the whole tray is the same age and grown under the same light, which is another reason to sow thinly and evenly.
You can exaggerate the difference deliberately. Grow the seedlings warm for a few days after emergence, then drop them to around 45 to 50F (7 to 10C) for two or three days. The single seedlings green up hard in the cold; the doubles stay pale and stand out clearly. Sort them then, transplant only the pale, large-leaved ones, and compost the rest without regret.
| Trait at the seedling stage | Likely double | Likely single |
|---|---|---|
| Leaf color | Pale yellow-green | Deep or gray-green |
| Leaf size at the same age | Larger, broader | Smaller, narrower |
| Leaf shape | Rounder, more spoon-like | More pointed, upright |
| Vigor | Slightly slower, chunkier | Faster, thinner |
| After a two to three day chill | Stays pale | Darkens noticeably |
Not every strain sorts this cleanly, and no strain gives a hundred percent. Sort generously rather than precisely: if you want twenty double plants, raise fifty seedlings and keep the palest twenty five.
Transplanting seedlings, hardening and planting on
Transplant at the first true leaf, holding a leaf rather than the stem, and set the seedlings deep enough that the seed leaves sit just above the compost. Stock makes a fine root system that resents drying, so pot into three inch (8 cm) pots or deep cells and keep them cool and bright, around 50F (10C) at night, until they go out.
Harden off over ten days or so, giving increasing outdoor time. Plant out at eight to twelve inches (20 to 30 cm) apart for branching kinds and six to eight inches (15 to 20 cm) for single-spike kinds, into ground that drains freely. Stock will not tolerate sitting wet, and a heavy, cold, badly drained bed kills more plants than any pest.
Set the plants out young. A stock that has stood in its pot until the roots circle rarely makes a full spike afterwards, and the root check often shows up as a short, one-sided flower head six weeks later.
What to write down this year
Three notes will change how you sow next time. Record the date you sowed against the date the first spike opened, so you know exactly how many weeks the whole run takes in your garden. Record the weather in the fortnight after the seedlings had three or four true leaves, because that is the window in which the cold spell has to land. And record what proportion of your seedlings sorted as doubles, and whether the pale ones did in fact open double.
Also note where the plants stood. Scent is the point of this plant, and a spot that carried it well or badly is worth remembering by position, not by a vague impression. A short line such as which bed, which side of the path, and whether you could smell it from a seat, is worth more next spring than any general advice.