Fertilising guide

How to fertilise Hemp-leaved Marshmallow (Althaea cannabina)— schedule & NPK

Also called Hemp-leaved Marshmallow, Cannabis-leaved Marshmallow, Hempweed Mallow.

More about hemp-leaved marshmallow

About Hemp-leaved Marshmallow

Althaea cannabina · also called Hemp-leaved Marshmallow, Cannabis-leaved Marshmallow · herb

Althaea cannabina is a tall, graceful Mediterranean herb with deeply divided, hemp-like leaves and small, delicate pink flowers borne over a long season. Traditionally used in herbalism similarly to common marshmallow (A. officinalis) for its mucilaginous roots and leaves. Drought-tolerant and attractive to pollinators; well-suited to herb gardens and naturalistic borders in warm climates.

Growth habit: Tall, branching perennial herb with erect to arching stems and finely dissected, palmate leaves resembling hemp foliage

Watch for — Flea beetles: Small round holes in leaves indicate flea beetle feeding. Damage is cosmetic on established plants. Protect seedlings with fleece or sticky traps.

What fertiliser hemp-leaved marshmallow actually wants — and why

Hemp-leaved Marshmallow is a soft, fast leafy herb that you harvest hard — a modest balanced feed keeps tender growth coming without tipping it into bland or bolting.

A balanced general feed (even N-P-K) at modest strength — enough nitrogen to keep replacing the leaves you pick, but not so much that flavour thins or it bolts to seed.

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 hemp-leaved marshmallow: 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 hemp-leaved marshmallow, 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 hemp-leaved marshmallow:

Minimal feeding required. In very poor soils, a single application of balanced fertiliser in spring is sufficient. Avoid nitrogen-rich feeds which produce lush, weak growth at the expense of flowers. In practice: a balanced liquid feed every few weeks through the main growing and harvesting season (spring through early autumn), more often the harder you are picking it.

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

Half strength is a sensible default for hemp-leaved marshmallow — enough to fuel regrowth after cutting, gentle enough that the leaves stay aromatic rather than watery.

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

Signs you are over-feeding hemp-leaved marshmallow

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

Fast, soft, pale growth with diluted, less aromatic flavour.
Early bolting (running to flower) and a bitter edge.
Salt crust and scorched tips on container plants.

Signs you are under-feeding hemp-leaved marshmallow

Pale, slow regrowth after cutting and small leaves.
A tired, stalled plant that cannot keep up with harvesting.
Yellowing older leaves in a long-spent pot.

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

Flushing and leaching the salts

Pot-grown hemp-leaved marshmallow builds up feed salts quickly — water until it drains each time and flush the pot with plain water every few weeks, especially on a sunny windowsill.

Organic vs synthetic feeds for hemp-leaved marshmallow

Organic options

A diluted seaweed feed or worm-casting tea keeps soft growth coming without overdoing it. UK: dilute seaweed or Westland; US: Espoma Garden-tone or Neptune's Harvest. Gentle, hard to overdo, flavour-friendly.

Synthetic / liquid feeds

A balanced liquid feed at half strength through harvesting — UK: Phostrogen, Baby Bio or Westland; US: Miracle-Gro all-purpose at half strength. Fast regrowth; just do not overdo the nitrogen.

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 hemp-leaved marshmallow — frequently asked questions

What fertiliser does hemp-leaved marshmallow need?

A balanced general feed (even N-P-K) at modest strength — enough nitrogen to keep replacing the leaves you pick, but not so much that flavour thins or it bolts to seed. Hemp-leaved Marshmallow is a soft, fast leafy herb that you harvest hard — a modest balanced feed keeps tender growth coming without tipping it into bland or bolting.

How often should I feed hemp-leaved marshmallow?

Minimal feeding required. In very poor soils, a single application of balanced fertiliser in spring is sufficient. Avoid nitrogen-rich feeds which produce lush, weak growth at the expense of flowers. Minimal feeding required. In very poor soils, a single application of balanced fertiliser in spring is sufficient. Avoid nitrogen-rich feeds which produce lush, weak growth at the expense of flowers. In practice: a balanced liquid feed every few weeks through the main growing and harvesting season (spring through early autumn), more often the harder you are picking it.

What strength of feed for hemp-leaved marshmallow?