Fertilising guide

How to fertilise Spencer Mixed sweet pea (Lathyrus odoratus 'Spencer Mixed')— schedule & NPK

Also called Spencer Mixed sweet pea, Sweet pea, Spenser sweet pea.

More about spencer mixed sweet pea

About Spencer Mixed sweet pea

Lathyrus odoratus 'Spencer Mixed' · also called Spencer Mixed sweet pea, Sweet pea · flowering

Spencer Mixed sweet pea is the classic large-flowered, intensely fragrant climbing annual, producing ruffled blooms in mixed shades of white, pink, lilac, mauve, and purple from early summer. It climbs to 1.8–2.5 m and needs cool roots, a support structure, and regular picking to keep flowering. Seeds and pods are toxic — do not eat.

Growth habit: Vigorous annual climbing vine with winged stems, pinnate leaves ending in tendrils, and large ruffled, waved flowers in loose racemes of 3–7 blooms

What fertiliser spencer mixed sweet pea actually wants — and why

Spencer Mixed 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 spencer mixed 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 spencer mixed 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 spencer mixed sweet pea:

The dormant-season rule matters more than the exact interval: skip feeding entirely when spencer mixed 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 spencer mixed sweet pea

Follow the flowering-feed label rate for spencer mixed 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 spencer mixed 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 spencer mixed sweet pea watering schedule.

Signs you are over-feeding spencer mixed sweet pea

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for spencer mixed 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 spencer mixed 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 spencer mixed sweet pea care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

Container-grown spencer mixed 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 spencer mixed 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 spencer mixed sweet pea — frequently asked questions

What fertiliser does spencer mixed 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. Spencer Mixed 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 spencer mixed sweet pea?

Apply a balanced slow-release fertiliser or well-rotted compost before planting. Feed every 2–3 weeks with a high-potassium liquid feed (e.g., tomato fertiliser) once flowering begins to prolong blooming. Avoid high-nitrogen feeds, which produce lush stems and poor flowers. Apply a balanced slow-release fertiliser or well-rotted compost before planting. Feed every 2–3 weeks with a high-potassium liquid feed (e.g., tomato fertiliser) once flowering begins to prolong blooming. Avoid high-nitrogen feeds, which produce lush stems and poor flowers. 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 spencer mixed sweet pea?

What does over-feeding spencer mixed 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 spencer mixed 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 spencer mixed sweet pea?