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Fertilising guide

How to fertilise Tall Verbena (Verbena bonariensis)— schedule & NPK

Also called tall verbena, purpletop vervain, Argentinian vervain.

More about tall verbena

About Tall Verbena

Verbena bonariensis · also called tall verbena, purpletop vervain · flowering

Verbena bonariensis, tall verbena, is an airy South American perennial sending wiry, near-leafless stems topped with clusters of small lilac-purple flowers from midsummer to autumn. Loved for its see-through height and butterfly appeal, it wants full sun and well-drained soil, is drought-tolerant, and self-seeds freely in milder gardens.

Growth habit: Tall, slender, see-through perennial (often short-lived or grown as an annual) with stiff, branching, square stems, very few leaves, and flat-topped clusters of tiny flowers held high.

Watch for — Flopping in shade or rich soil: Stems lean when light is low or feeding is heavy. Give full sun and lean soil, or grow through neighbouring plants for support.

What fertiliser tall verbena actually wants — and why

Tall Verbena is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.

A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula.

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 tall verbena: 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 tall verbena, 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 tall verbena:

Light feeder. A single balanced feed or thin compost mulch in spring is sufficient. Rich feeding promotes soft, floppy growth at the expense of the wiry, self-supporting habit that makes this plant valued. Treat that as sparingly through the growing season between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.

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

Half strength is the safe default for tall verbena — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.

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

Signs you are over-feeding tall verbena

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

Signs you are under-feeding tall verbena

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

Flushing and leaching the salts

Flush the pot of tall verbena with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.

Organic vs synthetic feeds for tall verbena

Organic options

A diluted seaweed or worm-casting feed, or fish emulsion if you can tolerate the smell indoors. UK: Westland or Baby Bio Organic, dilute seaweed; US: Espoma Indoor! or Neptune's Harvest fish & seaweed. Slow, gentle and hard to overdo.

Synthetic / liquid feeds

A general-purpose houseplant liquid at half strength — UK: Baby Bio, Westland Houseplant Feed or Phostrogen; US: Miracle-Gro Indoor Plant Food or Schultz. Convenient and fast-acting; the only risk is overdoing it.

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 tall verbena — frequently asked questions

What fertiliser does tall verbena need?

A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula. Tall Verbena is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.

How often should I feed tall verbena?

Light feeder. A single balanced feed or thin compost mulch in spring is sufficient. Rich feeding promotes soft, floppy growth at the expense of the wiry, self-supporting habit that makes this plant valued. Light feeder. A single balanced feed or thin compost mulch in spring is sufficient. Rich feeding promotes soft, floppy growth at the expense of the wiry, self-supporting habit that makes this plant valued. Treat that as sparingly through the growing season between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.

What strength of feed for tall verbena?

Half strength is the safe default for tall verbena — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.

What does over-feeding tall verbena look like?

Brown, crispy leaf tips and edges with no sign of underwatering. A white, crusty salt deposit on the soil surface or pot rim. Weak, pale, stretched new growth that flops. Lower leaves yellow and drop while the soil is correctly watered. Feeding tall verbena year-round on a fixed schedule, including dark winter months, is the most common mistake — it cannot use the nutrients in low light and the surplus simply burns the roots and crusts the soil.

Should I flush the soil of tall verbena?

Flush the pot of tall verbena with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.

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