Fertilising guide
How to fertilise Blue Potato Bush (Lycianthes rantonnetii)— schedule & NPK
Also called Blue Potato Bush, Paraguay Nightshade, Blue Solanum.
More about blue potato bush
About Blue Potato Bush
Lycianthes rantonnetii · also called Blue Potato Bush, Paraguay Nightshade · flowering
Lycianthes rantonnetii (formerly Solanum rantonnetii) is a South American shrub or scrambling climber smothered for months in small, bright violet-blue flowers with yellow centres, followed by small red berries. Vigorous and sun-loving, it thrives in warm gardens, on patios as a standard or scrambler, and in frost-prone climates as a container specimen. All parts are toxic.
Growth habit: Sprawling to semi-climbing evergreen shrub; trained as a standard, wall shrub, or scrambler
What fertiliser blue potato bush actually wants — and why
Blue Potato Bush 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 blue potato bush: 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 blue potato bush, 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 blue potato bush:
Feed with a high-potash liquid fertiliser (e.g., a tomato feed) every 7-10 days from spring through summer to support continuous flowering. A slow-release balanced fertiliser incorporated at repotting supplements liquid feeds. Do not fertilise in autumn and winter. 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 blue potato bush 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 blue potato bush
Follow the flowering-feed label rate for blue potato bush, 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 blue potato bush first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the blue potato bush watering schedule.
Signs you are over-feeding blue potato bush
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for blue potato bush:
- 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 blue potato bush
- 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 blue potato bush care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Container-grown blue potato bush 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 blue potato bush
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 blue potato bush — frequently asked questions
What fertiliser does blue potato bush 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. Blue Potato Bush 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 blue potato bush?
Feed with a high-potash liquid fertiliser (e.g., a tomato feed) every 7-10 days from spring through summer to support continuous flowering. A slow-release balanced fertiliser incorporated at repotting supplements liquid feeds. Do not fertilise in autumn and winter. Feed with a high-potash liquid fertiliser (e.g., a tomato feed) every 7-10 days from spring through summer to support continuous flowering. A slow-release balanced fertiliser incorporated at repotting supplements liquid feeds. Do not fertilise in autumn and winter. 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 blue potato bush?
Follow the flowering-feed label rate for blue potato bush, 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 blue potato bush 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 blue potato bush 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 blue potato bush?
Container-grown blue potato bush 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
- Blue Potato Bush care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water blue potato bush — 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 butterfly bush
- How to fertilise bodinier's beautyberry
- How to fertilise blue blossom
- All 6887 fertilising guides in the Growli library