Fertilising guide
How to fertilise Petunia axillaris (Petunia axillaris)— schedule & NPK
Also called White Moon Petunia, Large White Petunia.
More about petunia axillaris
About Petunia axillaris
Petunia axillaris · also called White Moon Petunia, Large White Petunia · flowering
Petunia axillaris is a wild South American species and a key parent of garden petunias, bearing large, pure-white, funnel-shaped flowers that are strongly fragrant in the evening to attract hawkmoths. A sprawling, somewhat sticky-leaved tender perennial usually grown as a half-hardy annual, it prefers full sun and free-draining, fertile soil and flowers all summer.
Growth habit: Sprawling to weakly upright, branching habit with sticky-hairy stems and leaves; flowers continuously through summer, the blooms opening and releasing scent towards evening.
What fertiliser petunia axillaris actually wants — and why
Petunia axillaris 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 petunia axillaris: 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 petunia axillaris, 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 petunia axillaris:
Feed moderately; less greedy than the big hybrids but still benefits from a balanced or high-potash liquid feed every 2-3 weeks through summer, or slow-release fertiliser at planting. Excess nitrogen produces lush foliage at the expense of the fragrant white flowers. For a hungry bloomer that means feeding regularly — every 2-3 weeks — 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 petunia axillaris 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 petunia axillaris
Follow the flowering-feed label rate for petunia axillaris, 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 petunia axillaris first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the petunia axillaris watering schedule.
Signs you are over-feeding petunia axillaris
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for petunia axillaris:
- 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 petunia axillaris
- 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 petunia axillaris care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Container-grown petunia axillaris 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 petunia axillaris
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 petunia axillaris — frequently asked questions
What fertiliser does petunia axillaris 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. Petunia axillaris 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 petunia axillaris?
Feed moderately; less greedy than the big hybrids but still benefits from a balanced or high-potash liquid feed every 2-3 weeks through summer, or slow-release fertiliser at planting. Excess nitrogen produces lush foliage at the expense of the fragrant white flowers. Feed moderately; less greedy than the big hybrids but still benefits from a balanced or high-potash liquid feed every 2-3 weeks through summer, or slow-release fertiliser at planting. Excess nitrogen produces lush foliage at the expense of the fragrant white flowers. For a hungry bloomer that means feeding regularly — every 2-3 weeks — right through flowering across the main season (spring through early autumn), tapering as blooming ends.
What strength of feed for petunia axillaris?
Follow the flowering-feed label rate for petunia axillaris, or half strength if feeding very frequently. These plants genuinely use the nutrients — under-feeding shows up fast as a thin display.
What does over-feeding petunia axillaris look like?
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. Using a high-nitrogen general feed on petunia axillaris is the headline mistake — you grow a big leafy plant with few flowers. The second is simply under-feeding a genuinely hungry bloomer and getting a sparse, short display.
Should I flush the soil of petunia axillaris?
Container-grown petunia axillaris 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.
Keep reading
- Petunia axillaris care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water petunia axillaris — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise peace lily
- How to fertilise bird of paradise
- How to fertilise hoya
- All 5561 fertilising guides in the Growli library