Germination temperature
About 21 °C (70 °F) or warmer.
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Mexican sunflower is a tall, heat-loving annual with velvety orange flowers that butterflies love. It sprouts in 5-10 days in warm conditions and thrives in poor, dry soil.
About 21 °C (70 °F) or warmer.
Shallow: only a light covering of soil.
About 5-10 days.
Light is beneficial: sow shallowly.
None needed.
Both work; start in trays 6-8 weeks before planting out, or sow directly in warm soil.
The seed is long, narrow and easy to handle. Sow two seeds per spot or cell and keep the stronger seedling.
Not needed. Tithonia seed takes up water readily.
Not needed. This is a frost-tender warm-season annual from Mexico and Central America; it only needs warmth.
Not needed. Sow into warm, moist soil.
The University of Alaska Fairbanks seed-starting chart gives 21 °C (70 °F). Seed sown into cold soil is slow and patchy, so outdoors wait until the weather is reliably warm.
Cover only slightly. The Alaska chart lists a slight covering, and the University of Wisconsin-Madison advises sowing shallowly because light is beneficial for germination. A dusting of fine soil or vermiculite is enough.
Any well-drained soil. Mexican sunflower does best in poorer soil (NC State Extension); rich soil and heavy feeding give lush leaves and weak stems.
Keep the surface evenly moist until the seedlings appear. Because the seed is shallow, check it daily in hot or windy weather.
Do not bury the seed deeply; a thin cover still lets light reach it. Once up, seedlings need full sun to stay sturdy.
About 5-10 days at around 21 °C (70 °F).
Start seed indoors 6-8 weeks before planting out (University of Wisconsin-Madison) and move plants out once the weather is warm. Handle them gently and do not let them become root-bound in small pots.
Space plants about 60 cm (2 ft) apart so they lean on each other for support, or 90-120 cm (3-4 ft) apart if you stake each plant.
Pinch out the growing tip of young plants, or shear established plants back by about a third in early summer, to get bushier, slightly shorter plants with more flowers.
Cause: rich soil or too much fertiliser. Fix: grow in lean soil and do not feed; Mexican sunflower prefers poor ground.
Cause: tall, brittle stems; plants reach 1-2 m (3-6 ft). Fix: stake plants or plant them in a group, and choose a spot sheltered from strong wind.
Cause: sown too late in a short or cool season. Fix: sow early in the warm season or start plants in trays so they have time to bloom.
Cause: cold soil or seed buried too deep. Fix: sow shallowly once soil is warm, or start seed in trays at about 21 °C (70 °F).
Mexican sunflower tolerates heat, drought and dry soil (NC State Extension). In the Indian plains sow it as the weather warms, for flowers through the hot months; in the hills sow after the last frost.
Most plants reach 1.2-1.8 m (4-6 ft) or more; compact varieties stay around 90 cm-1.2 m (3-4 ft). Use them as a quick summer screen or backdrop.
Removing faded flowers prolongs flowering. The bright flowers are popular with butterflies and bees.
Tithonia rotundifolia is a frost-tender annual. It is different from Tithonia diversifolia, the shrubby tree marigold, which has become an invasive weed in parts of tropical Asia and Africa. Remove spent flowerheads before seed drops if you do not want self-sown seedlings.
Grow Mexican sunflower for tall, fiery orange flowers that keep butterflies busy all summer.
Only just under the surface. Light helps germination, so cover the seed with a thin dusting of soil or vermiculite and keep it moist.
Tithonia rotundifolia is an annual that can self-sow; it has been declared an invasive weed in South Africa. The shrubby Tithonia diversifolia is a different, more aggressive species. Deadhead before seed sets if you want to limit spread.
Rich soil and fertiliser push leaf growth at the expense of flowers. Grow it in lean, well-drained soil in full sun and pinch young plants to keep them bushier.
Often yes. Plants grow 1-2 m tall with brittle stems, so stake them or plant them about 60 cm apart in a group so they support each other.