Fertilising guide

How to fertilise Nasturtium (Tropaeolum majus)— schedule & NPK

Also called Indian cress, monk's cress, garden nasturtium.

About Nasturtium

Tropaeolum majus · also called Indian cress, monk's cress · flowering

Nasturtiums are easy quick-growing annuals with circular leaves and trumpet-shaped flowers in red, orange, and yellow. Bush and trailing types available. Leaves, flowers, and seeds are edible with peppery flavour. Pet-safe and edible.

Garden nasturtium (Tropaeolum majus) is a fast, trailing or climbing tender annual from the Andes of South America; both flowers and leaves are edible with a peppery, watercress-like taste.

Do not feed nitrogen; low-fertility, low-nitrogen conditions are required for good bloom, as too much nitrogen forces leafy growth over flowers.

Growth habit: Bushy or trailing annual

Watch for — All leaves, no flowers: Too rich soil or too much nitrogen.

Sources: hort.extension.wisc.edu, rhs.org.uk, extension.umn.edu

What fertiliser nasturtium actually wants — and why

Nasturtium flowers best on poor soil — feed it and you get a lush leafy plant with very few blooms, the exact opposite of what you want.

Little or nothing. Rich, especially nitrogen-rich, soil pushes foliage at the expense of flowers in this plant — lean ground is the technique, not a deficiency.

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 nasturtium: 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 nasturtium, 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 nasturtium:

None needed; rich soil produces leaf at the expense of flowers. In practice: no routine feeding at all for nasturtium — at most a thin compost mulch for soil structure, never a flowering or nitrogen feed.

The dormant-season rule matters more than the exact interval: skip feeding entirely when nasturtium 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 nasturtium

None is the correct answer for nasturtium. The flower-versus-foliage trade-off is the whole point: hold back and you get the display.

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

Signs you are over-feeding nasturtium

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

Abundant leafy growth and very few flowers (the classic over-rich symptom).
Soft, floppy stems and a sprawling, leafy habit.
Scorched edges and salt crust if it has been fed in a container.

Signs you are under-feeding nasturtium

Effectively never an issue — these plants flower on poverty.
Only on genuinely dead soil: weak, thin growth and few blooms.
A short-lived plant in completely spent container compost.

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

Flushing and leaching the salts

If nasturtium has accidentally been fed and is all leaf, a plain-water flush plus a move to leaner soil resets it; otherwise no flushing is needed because you are not feeding it.

Organic vs synthetic feeds for nasturtium

Organic options

A thin compost mulch for soil structure is the absolute most; mostly, give it nothing. UK/US: leave it lean — no manure, no liquid feed. Poor soil is the active ingredient here.

Synthetic / liquid feeds

None. Synthetic feeds, particularly anything with appreciable nitrogen, directly suppress flowering in nasturtium.

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 nasturtium — frequently asked questions

What fertiliser does nasturtium need?

Little or nothing. Rich, especially nitrogen-rich, soil pushes foliage at the expense of flowers in this plant — lean ground is the technique, not a deficiency. Nasturtium flowers best on poor soil — feed it and you get a lush leafy plant with very few blooms, the exact opposite of what you want.

How often should I feed nasturtium?

None needed; rich soil produces leaf at the expense of flowers. None needed; rich soil produces leaf at the expense of flowers. In practice: no routine feeding at all for nasturtium — at most a thin compost mulch for soil structure, never a flowering or nitrogen feed.

What strength of feed for nasturtium?