Fertilising guide
How to fertilise Sweet pea (Lathyrus odoratus)— schedule & NPK
Also called annual sweet pea, garden sweet pea.
About Sweet pea
Lathyrus odoratus · also called annual sweet pea, garden sweet pea · flowering
Sweet peas are cool-season climbing annuals grown for fragrant ruffled flowers in every colour but yellow. Need cool roots, support, and constant deadheading. Toxic to pets — and the seeds are toxic to people too; never confuse with edible peas.
Sweet pea (Lathyrus odoratus) is a climbing annual legume from the central Mediterranean (Sicily and southern Italy), prized above all for the strong fragrance bred into many cultivars.
As a legume it fixes some nitrogen; feed with a balanced or potash-leaning fertilizer rather than high nitrogen to favor flowers over foliage.
Growth habit: Climbing cool-season annual
Watch for — No flowers: Too rich soil or too much nitrogen; pinch tips early for branching.
Sources: rhs.org.uk, rhs.org.uk, missouribotanicalgarden.org
What fertiliser sweet pea actually wants — and why
Sweet pea 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 sweet pea: 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 sweet pea, 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 sweet pea:
Balanced feed at planting; high-potash feed every 2-3 weeks during flowering. 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 sweet pea 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 sweet pea
Follow the flowering-feed label rate for sweet pea, 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 sweet pea first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the sweet pea watering schedule.
Signs you are over-feeding sweet pea
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for sweet pea:
- 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 sweet pea
- 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 sweet pea care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Container-grown sweet pea 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 sweet pea
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 sweet pea — frequently asked questions
What fertiliser does sweet pea 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. Sweet pea 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 sweet pea?
Balanced feed at planting; high-potash feed every 2-3 weeks during flowering. Balanced feed at planting; high-potash feed every 2-3 weeks during flowering. 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 sweet pea?
Follow the flowering-feed label rate for sweet pea, 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 sweet pea 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 sweet pea 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 sweet pea?
Container-grown sweet pea 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
- Sweet pea care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water sweet pea — 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 200 fertilising guides in the Growli library