Fertilising guide

How to fertilise Mexican sunflower (Tithonia rotundifolia)— schedule & NPK

Also called Mexican sunflower, Tithonia.

More about mexican sunflower

About Mexican sunflower

Tithonia rotundifolia · also called Mexican sunflower, Tithonia · flowering

Mexican sunflower is a vigorous, heat-loving half-hardy annual from Mexico and Central America producing vivid orange-red, daisy-like blooms up to 8 cm across on tall, branching plants from midsummer to first frost. An exceptional pollinator plant and cut flower. Thrives in poor, dry soil in full sun; struggles with rich soil, excess nitrogen, and root disturbance.

Growth habit: Tall, erect, branching half-hardy annual; produces a thick central stem with lateral branches each terminating in a flower

Watch for — Stem lodging and breakage: Tall stems on the species type are hollow and brittle. Stake plants in exposed positions once 60 cm tall. Avoid excessive nitrogen feeding, which makes stems even weaker. Grow compact cultivars ('Goldfinger') in windy sites.

What fertiliser mexican sunflower actually wants — and why

Mexican sunflower is a heavy-blooming flower with a big appetite — a regular high-potash feed through the season is what drives a long, dense display.

A high-potassium ("high-potash") flowering feed — tomato-style or a dedicated bloom/rose feed. Potassium powers flowering; a high-nitrogen feed gives you a leafy plant with disappointing bloom.

For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for mexican sunflower: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.

How often to feed mexican sunflower, and which months

Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For mexican sunflower:

Apply a low-nitrogen, high-phosphorus and potassium fertiliser sparingly at planting. Avoid further fertilisation in poor soils — in average garden soil, no additional feeding is required. Excess nitrogen is the most common cultivation mistake. For a hungry bloomer that means feeding regularly — sparingly through the growing season — right through flowering across the main season (spring through early autumn), tapering as blooming ends.

The dormant-season rule matters more than the exact interval: skip feeding entirely when mexican sunflower is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.

What strength to mix for mexican sunflower

Follow the flowering-feed label rate for mexican sunflower, or half strength if feeding very frequently. These plants genuinely use the nutrients — under-feeding shows up fast as a thin display.

Feeding always goes onto already-damp soil, never dry roots — water mexican sunflower first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the mexican sunflower watering schedule.

Signs you are over-feeding mexican sunflower

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for mexican sunflower:

Lots of lush leaves but few flowers (too much nitrogen).
Scorched leaf edges and salt crust from too-strong or too-frequent feeds.
Soft, sappy growth prone to aphids and mildew.

Signs you are under-feeding mexican sunflower

Sparse, small, short-lived flowers and pale foliage.
A tired plant that stops blooming early in the season.
Weak growth and poor repeat-flowering after the first flush.

If the symptoms point at watering, light or roots rather than nutrition, the full mexican sunflower care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

Container-grown mexican sunflower accumulates feed salts fast with frequent feeding — water until it drains each time and flush pots with plain water every few weeks to prevent scorch.

Organic vs synthetic feeds for mexican sunflower

Organic options

A liquid comfrey or seaweed feed (naturally potassium-rich) plus compost or well-rotted manure as a mulch. UK: comfrey feed, organic Tomorite, or rose feed; US: Espoma Rose-tone or Neptune's Harvest. Feeds and improves soil.

Synthetic / liquid feeds

A high-potash flowering feed on a regular cadence — UK: Tomorite (Levington), Phostrogen or a specialist rose feed; US: Miracle-Gro Bloom Booster or a rose food. Fast, reliable bloom response.

Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.

Fertilising mexican sunflower — frequently asked questions

What fertiliser does mexican sunflower need?

A high-potassium ("high-potash") flowering feed — tomato-style or a dedicated bloom/rose feed. Potassium powers flowering; a high-nitrogen feed gives you a leafy plant with disappointing bloom. Mexican sunflower is a heavy-blooming flower with a big appetite — a regular high-potash feed through the season is what drives a long, dense display.

How often should I feed mexican sunflower?

Apply a low-nitrogen, high-phosphorus and potassium fertiliser sparingly at planting. Avoid further fertilisation in poor soils — in average garden soil, no additional feeding is required. Excess nitrogen is the most common cultivation mistake. Apply a low-nitrogen, high-phosphorus and potassium fertiliser sparingly at planting. Avoid further fertilisation in poor soils — in average garden soil, no additional feeding is required. Excess nitrogen is the most common cultivation mistake. For a hungry bloomer that means feeding regularly — sparingly through the growing season — right through flowering across the main season (spring through early autumn), tapering as blooming ends.

What strength of feed for mexican sunflower?