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A sunflower runs from sowing to seed in roughly 90 to 130 days depending on the type, and the whole thing happens in one growing season. That makes the calendar unusually tight: there is no dormant period to correct mistakes in, and a job done two weeks late is usually a job that cannot be done at all.
Four decisions carry most of the outcome. Sowing into soil that is genuinely warm, staking before the plant leans, watering without fail from bud to petal drop, and covering the head before the seed starts disappearing. Everything else is tidying up.
| Period | Main jobs | What to avoid |
|---|---|---|
| Before sowing | Dig in modest compost, choose the site | Heavy nitrogen feeding |
| Soil above 55F (13C) | Sow direct, two seeds per station | Sowing into cold wet soil |
| First true leaves | Thin to one, remove bird netting | Leaving two plants together |
| Knee high | Drive the stake, first tie | Waiting until it leans |
| Rapid growth | Tie every 18 in (45 cm), deep watering | Frequent shallow watering |
| Bud showing color | Switch to low nitrogen, final tie | Letting the soil dry |
| Flowering | Water without fail, leave pollinators alone | Feeding, or cutting side buds on branching types |
| Petals dropping | Watch the back of the head | Cutting the head now |
| Back of head yellowing | Bag against birds | Assuming the birds will wait |
| Back brown, neck bent | Cut with 12 in (30 cm) of stem | Cutting on a wet day |
| After harvest | Dry, thresh, store, cut down stems | Leaving moldy heads on the plot |
From sowing to knee high
The first six weeks are about getting an evenly spaced stand of single, well rooted plants. Sow direct once the soil holds 55F (13C), one inch (2.5 cm) deep, two seeds per station, and net the row against birds until the true leaves are out. Thin to one plant at the first true leaf stage by cutting the weaker at soil level.
Resist feeding through this period. A sunflower that has to send its taproot down looking for water builds the deep anchorage it needs later. Feeding early gives soft growth and a plant that leans in the first storm.
- Prepare modestly Dig in compost a couple of weeks before sowing and leave it at that. Rich, freshly manured ground gives leaf and a weak stem.
- Sow when the soil is genuinely warm Three consecutive mornings above 55F (13C) at two inches (5 cm) down. Emergence then takes five to ten days instead of three weeks.
- Net the row for two weeks Birds pull emerging seedlings for the seed still attached. Remove the netting once the first true leaves are open.
- Thin early and decisively Cut, do not pull, the weaker seedling at the first true leaf stage. Left a fortnight, both plants end up thin.
- Mulch once the plants are a hand tall Two inches (5 cm) of mulch holds moisture and keeps weeds down without you having to hoe next to a shallow-rooted seedling.
The staking window is short
There is a period of about two weeks, when the plant is between 18 and 24 inches (45 to 60 cm) tall, in which staking is easy and completely effective. Before that you cannot judge where the plant will sit; after that the root ball is wide enough that a stake driven beside it cuts roots, and the plant may already have shifted in a windy spell.
Get the stake in during that window and the rest of the season is a matter of adding ties as the plant grows and checking the lower ones have not tightened. Miss it and you spend the summer propping.
| Plant height | Staking action | Result if you skip it |
|---|---|---|
| Under 18 in (45 cm) | Too early to judge | Not applicable |
| 18 to 24 in (45 to 60 cm) | Drive stake, first tie | The whole point of the window |
| 2 to 4 ft (60 to 120 cm) | Add ties as it grows | Stem bows permanently between ties |
| Over 4 ft (1.2 m) | Too late to drive without root damage | Lean develops, root plate tears |
Drive the stake on the windward side and keep ties in a figure of eight with a finger's width of slack. Check the lowest tie fortnightly; the stem can double in girth in two weeks.
Flowering: the fortnight that decides the head
From the bud showing color through to the last petal dropping is around three weeks, and it is the period in which head size and seed fill are settled. Water deeply twice a week without fail, because water stress now shows up permanently as a smaller head and a hollow, unfilled center.
Stop feeding nitrogen once the bud appears and switch to something with more potassium if you feed at all. Leave the open flower alone otherwise: pollinators are doing the work that determines how much of the head fills with seed, and there is nothing useful to add.
| Stage | Days from bud | Job |
|---|---|---|
| Bud shows color | 0 | Final tie, switch feed, check watering |
| Petals unfurling | 5 to 8 | Deep water twice a week |
| Disc florets open | 8 to 15 | Leave alone for pollinators |
| Petals fading | 15 to 21 | Watch for the first bird interest |
| Last petal drops | About 21 | Start checking the back of the head |
On branching types this whole sequence repeats on each side bud for weeks. Keep watering through it; the later heads are smaller mainly because the plant went short of water, not because they were always going to be.
Seed, clear up, and what to write down
After the petals drop, the head needs three to five more weeks before the seed is mature. Bag the head as soon as the back begins to yellow, cut when the back is brown, the bracts are dry and papery and the neck has bent, and dry the head face down somewhere airy for two to three weeks before threshing.
Once the heads are off, cut the stems down and get them off the plot; the thick stems take a long time to rot and can carry disease over. Then write the season down while it is fresh, because next year's improvements all come from these numbers.
- Record sowing to first flower The number of days between the two, for the type you grew, in your garden. It is more reliable than any printed figure and it lets you time succession sowings properly.
- Record staking date and finished height Together these tell you next spring how tall a stake to buy and exactly when to drive it.
- Record the date birds first took seed It falls at much the same point each year. Knowing it means bagging heads before the damage, not after.
- Record head diameter against spacing Note what spacing produced what size of head. This settles the spacing question permanently and stops you crowding the row again.
- Note where each plant stood Tall sunflowers shade whatever is behind them, and heavy feeders should not follow into the same ground next season. A rough sketch is enough.
Sunflowers take a good deal out of the soil and the same ground planted year after year gives visibly smaller heads. Move the row and dig in compost where they stood.