Fertilising guide

How to fertilise Red larkspur (Delphinium nudicaule)— schedule & NPK

Also called Red larkspur, Scarlet larkspur, Orange larkspur.

More about red larkspur

About Red larkspur

Delphinium nudicaule · also called Red larkspur, Scarlet larkspur · flowering

A native Californian wildflower with nodding, scarlet to orange-red spurred flowers on slender, branching stems in spring and early summer. Much smaller and less vigorous than European delphiniums, it prefers well-drained, gritty soil in full sun and is a magnet for hummingbirds. Fully toxic to pets. Better treated as a seasonal perennial or cool-season annual in most gardens.

Growth habit: Small, upright to sprawling short-lived perennial; goes summer-dormant in hot, dry conditions

What fertiliser red larkspur actually wants — and why

Red larkspur 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 red larkspur: 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 red larkspur, 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 red larkspur:

Apply a low-nitrogen balanced fertilizer sparingly in early spring as growth begins. Avoid over-feeding, which produces lush but mildew-prone foliage at the expense of flowers. No feed needed once plants enter summer dormancy. In practice: no routine feeding at all for red larkspur — 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 red larkspur 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 red larkspur

None is the correct answer for red larkspur. 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 red larkspur first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the red larkspur watering schedule.

Signs you are over-feeding red larkspur

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

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 red larkspur

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 red larkspur care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

If red larkspur 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 red larkspur

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 red larkspur.

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 red larkspur — frequently asked questions

What fertiliser does red larkspur 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. Red larkspur 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 red larkspur?

Apply a low-nitrogen balanced fertilizer sparingly in early spring as growth begins. Avoid over-feeding, which produces lush but mildew-prone foliage at the expense of flowers. No feed needed once plants enter summer dormancy. Apply a low-nitrogen balanced fertilizer sparingly in early spring as growth begins. Avoid over-feeding, which produces lush but mildew-prone foliage at the expense of flowers. No feed needed once plants enter summer dormancy. In practice: no routine feeding at all for red larkspur — at most a thin compost mulch for soil structure, never a flowering or nitrogen feed.

What strength of feed for red larkspur?