Gadenin日本語Get the appWhen you sow decides how big the plant gets
This is the single decision that separates a thin, one-flush patch of cornflower from a waist-high thicket that cuts for two months. Seed sown in autumn germinates while the soil is still warm, makes a low rosette of narrow gray-green leaves, and spends the whole winter putting down a deep taproot while the top does almost nothing. When growth restarts in spring that root drives a plant that branches from the base into a dozen or more flowering stems and stands three feet (90 cm) tall. Seed sown in spring has to build the root and the top at the same time, and it flowers on four or five stems at half the height.
The catch is winter. An autumn sowing works where the ground does not freeze solid and where winter lows stay above roughly 10F (minus 12C). The rosette is genuinely hardy at that stage, far hardier than the flowering plant, but it will not survive being heaved out of the soil by repeated freeze and thaw, and it rots in ground that lies wet all winter. If your winters are colder or wetter than that, sow in earliest spring instead and accept the smaller plant, or start under cover in late winter and plant out as soon as the soil is workable.
Nothing about the sowing itself differs between the two seasons. The depth, the spacing and the watering are identical. Only the calendar changes, and with it the size of what you get.
| Sowing time | Winter it needs | Plant you get | Cutting season |
|---|---|---|---|
| Early autumn, six weeks before hard frost | Mild, lows above 10F (-12C), well drained | Three feet (90 cm), ten to fifteen stems | Long, starting in late spring |
| Late autumn, into cold soil | Mild, but germination is slow | Two to three feet (60 to 90 cm), fewer stems | Starts a fortnight later |
| Late winter under cover | Any, plants are protected | Two feet (60 cm), moderate branching | From early summer |
| Earliest spring, direct, as soon as workable | Any | Eighteen inches to two feet (45 to 60 cm), four to six stems | Short, midsummer only |
| Late spring | Any | Small, often single stemmed | Brief, and it bolts in heat |
Sow where it is to flower, not in pots
Cornflower makes a taproot early and resents having it broken. Seedlings moved from a seed tray check for a fortnight, branch less afterwards, and often flower on a single stem. If you must start under cover because of a cold winter, use deep cells or root trainers rather than open trays, sow two seeds per cell and pull the weaker, and plant out while the seedling still has only three or four true leaves. Once you can see roots circling the bottom of the cell you have already lost some of the height.
Direct sowing is easier and gives better plants. Choose open ground in full sun on soil that is not rich. Cornflower evolved as a weed of grain fields on thin, alkaline, well-drained ground, and it behaves accordingly: on fed, heavily manured soil it grows tall and soft and lies flat in the first storm. Do not dig compost in before sowing. Rake the surface to a reasonably fine tilth, take out perennial weed roots, and firm it lightly.
Sow half an inch (1.5 cm) deep. The seed is a small bristly cylinder with a tuft of hairs at one end, big enough to space by hand, and it needs darkness to germinate, so surface sowing fails. Either draw a shallow drill and space seeds two inches (5 cm) apart along it, or broadcast thinly over a patch and rake the seed in. At 60 to 70F (15 to 21C) it comes up in seven to ten days; in cold autumn soil around 50F (10C) it takes two to three weeks.
- Pick an open, sunny position and leave the soil lean Full sun and free drainage. Skip the compost and the fertilizer entirely. Rich ground produces soft growth that flops before the first flower opens and mildews in late summer.
- Rake to a fine tilth and firm it Break the surface down to crumbs the size of a pea and press it flat with the back of the rake. Seed that falls into cracks in rough ground germinates in tight clumps that are impossible to thin properly.
- Sow half an inch (1.5 cm) deep, two inches (5 cm) apart Draw a drill with the corner of a hoe, drop the seed along it, and pull the soil back over. The seed needs darkness, so do not leave it on the surface. Water the drill before sowing if the soil is dry, not after.
- Water once, then leave it alone until seedlings show One thorough soak settles the soil around the seed. After that water only if the surface is dust dry, because cornflower seed rots in cold ground that is kept wet.
- Thin in two stages, ending at nine to twelve inches (23 to 30 cm) Thin first to four inches (10 cm) once the seedlings have two true leaves, then to the final spacing a month later. Crowded plants make one stem each and mildew from midsummer; properly spaced ones branch from the base.
Thin harder than feels reasonable
Almost every disappointing patch of cornflower is an unthinned one. Left at two inches (5 cm), the plants draw each other up into thin single stems that flower once and are over in three weeks. Thinned to nine or twelve inches (23 to 30 cm), each plant branches from the base into the multi-stemmed bush that gives you the long cutting season. An autumn sowing deserves the wider end of that range because the plants get so much bigger; a spring sowing can sit at eight or nine inches (20 to 23 cm).
Thin in two stages so you keep a margin against losses from slugs and birds, and do it when the soil is damp so the surplus pulls out cleanly without disturbing the roots of the keepers. Thinnings do not transplant well, for the taproot reason above, so pull them and compost them rather than trying to line them out elsewhere. If you want more plants, sow a second patch rather than moving seedlings.
One useful trick with an autumn sowing: leave the final thinning until early spring. Winter losses are unpredictable, and going into the cold with plants at four inches (10 cm) gives you enough spare to end up at a full stand rather than a gappy row.
Sow a short succession rather than one big patch if you want flowers over a long stretch. An autumn sowing plus a spring sowing of the same length of row, in the same bed, keeps the cutting going from late spring right through summer, because the spring plants come into flower as the autumn ones start to tire.
Write down what you sowed and when it came up
The two dates worth recording are the sowing date and the date the first seedlings showed, because they tell you next year whether your autumn window was right. Sow too early and the plants go into winter too large and soft and rot at the crown; sow too late and they never make the root. The gap you are aiming for is around six weeks of growing weather before hard frost, and the only way to calibrate that for your own garden is to have written down what happened last time.
Also record where the patch was. Cornflower seeds itself freely, so the following spring you will find seedlings both where you sowed and well away from it, and a note or a photograph taken from a fixed point is the only way to tell a deliberate stand from a volunteer colony. That matters more than it sounds, because volunteers that come up in autumn behave like an autumn sowing and are worth keeping, while ones that appear in late spring rarely amount to much.