Gadenin日本語Get the appWait for soil above 55F (13C)
Sunflower seed germinates in soil from about 55F (13C) upwards, and fastest between 70 and 85F (21 to 29C). In cold, wet soil the seed sits without moving and rots or gets eaten before it can emerge. Push a soil thermometer two inches (5 cm) down first thing in the morning, and sow once you get three mornings in a row above 55F (13C).
At the right temperature you will see the seedling break the surface in five to ten days. Below that it can take three weeks, and a slow start is exactly when mice, birds and slugs take the seed. There is no advantage in sowing early: a sowing made two weeks later in warm soil usually overtakes the early one before it flowers.
| Soil temperature | Days to emerge | Verdict |
|---|---|---|
| Below 55F (13C) | Often never | Too early, seed rots |
| 55 to 65F (13 to 18C) | 10 to 14 | Workable, protect the row |
| 70 to 85F (21 to 29C) | 5 to 7 | Ideal |
| Above 90F (32C) | 4 to 6 | Fine, but keep the surface damp |
Frost kills sunflower seedlings outright. Sow direct only after your last expected frost date has passed, and keep a sheet of row cover within reach for a late cold night.
One inch deep, and the spacing decides the flower
Sow one inch (2.5 cm) deep in ordinary soil, and up to one and a half inches (4 cm) in light sand where the surface dries fast. Shallower than half an inch (1 cm) and the seedling comes up wearing its seed coat and can be pulled out by a bird in one tug.
Spacing is the decision people get wrong, because it controls the size of the head far more than feeding does. Close spacing gives you many small blooms on thin stems; wide spacing gives you fewer, much larger heads on stems that can hold them up. Decide what you want before you make the drill, because you cannot fix it afterwards without losing plants.
| What you want | Spacing in the row | Row spacing | Typical head |
|---|---|---|---|
| Big single heads for seed | 18 to 24 in (45 to 60 cm) | 30 in (75 cm) | 10 to 14 in (25 to 35 cm) across |
| Cutting stems | 9 to 12 in (23 to 30 cm) | 18 in (45 cm) | 4 to 6 in (10 to 15 cm) across |
| A screen or hedge | 12 in (30 cm) | Single row | Medium, on straight stems |
| Large container | One plant per 5 gal (20 L) | Not applicable | Depends on the type |
Sow direct rather than transplanting
A sunflower puts down a deep, fast taproot within days of germinating. Break or coil that root and the plant is permanently less stable, which matters enormously for a tall type that has to hold a heavy head in wind. Direct sowing is not just easier, it produces a better anchored plant.
If you must start under cover because of a short season or heavy bird pressure, use deep cells or three inch (7.5 cm) pots, sow one seed per cell, and plant out at no more than three true leaves. A sunflower held in a small pot until it is a foot tall will never catch up with one sown direct on the same day.
- Sow two seeds per station Push two seeds an inch (2.5 cm) deep and two inches (5 cm) apart at each spot you want a plant. Cover, firm gently with the back of your hand, and water the drill rather than the whole bed.
- Thin to the stronger one At the first true leaf stage, cut the weaker seedling off at soil level with scissors. Pulling it disturbs the taproot of the one you are keeping.
- Do not thin late Two sunflowers left together to a foot tall both end up thin and neither carries a decent head. Thin within a week of the true leaves appearing.
- Cover against birds until the seed leaves open Lay fine netting or a length of chicken wire over the row. Birds pull emerging seedlings for the seed still attached, and the risk ends once the first true leaves are out.
- Water the drill, not the bed Keep a band four inches (10 cm) wide along the row damp until emergence. Watering the whole bed brings up weeds you then have to pull next to a fragile seedling.
Save your own seed from a big head and you can afford to sow generously and thin hard. That is the cheapest route to well spaced, well fed plants.
Succession sowing for a long season
One sowing gives you two to three weeks of flower. If you want blooms right through to the first frosts, sow a short row every two weeks from the time the soil warms until about 80 days before your first expected frost. Later than that and the heads set but never fill.
Branching multi-headed types stretch the season on their own because side buds open in sequence, so with those you need fewer sowings. Single-stem types finish all at once, so those are the ones worth staggering.
| Sowing | Timing | What it gives you |
|---|---|---|
| First | Once soil holds 55F (13C) | Earliest flowers, tallest plants |
| Second | Two weeks later | Peak summer bloom |
| Third | Four weeks later | Late summer cutting |
| Last | 80 days before first frost | Autumn flowers, seed may not fill |
Write down the sowing so next year is easier
The single most useful thing to record is the sowing date next to the date the first flower opened, for each sowing you make. After one season you know your own days-to-flower figure, which is far more reliable than any figure printed on a packet, because it is measured in your soil and your summer.
Note the spacing you used and the head diameter you got alongside it. That pairing settles the spacing argument for good, and it stops you repeating the year you crammed plants in and got nothing but thin stems.
- Sowing date and soil temperature Record the morning soil reading you sowed on. A year later you will know whether your gut feeling about when the soil is warm is right or two weeks optimistic.
- Emergence date Note the day the first seedling breaks the surface. The gap between sowing and emergence tells you immediately whether the soil was warm enough.
- Position in the bed Sketch which end of the row held which sowing. Tall types shade whatever is north of them, and you will want to know that when you plan the following year.
- How many failed Count the stations that never came up. Consistent gaps at one end usually mean a dry patch or a mouse run, not bad seed.