Fertilising guide

How to fertilise Mizuna (Brassica rapa var. niposinica)— schedule & NPK

Also called Japanese mustard greens, Spider mustard.

More about mizuna

About Mizuna

Brassica rapa var. niposinica · also called Japanese mustard greens, Spider mustard · edible

Mizuna is a fast, vigorous Japanese salad brassica forming a feathery rosette of deeply serrated, glossy green leaves with a mild peppery-mustard tang. One of the easiest cut-and-come-again greens, it crops in 3-6 weeks, regrows after cutting, and is far slower to bolt than most leafy brassicas. It suits spring, autumn and even winter-protected sowings in cool, moist conditions.

Growth habit: Dense, upright-to-spreading rosette of slender stalks bearing finely dissected, fringed leaves; resprouts readily from the crown when cut, giving multiple harvests.

What fertiliser mizuna actually wants — and why

Mizuna feeds in two distinct phases — balanced to build the plant, then high-potassium the moment flowering starts to set and fill a heavy crop.

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 mizuna: 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 mizuna, 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 mizuna:

Light-to-moderate feeder. Compost-enriched soil usually meets its needs; for repeated cut-and-come-again harvests, a nitrogen-rich liquid feed after each cutting keeps regrowth fast and leaves tender and mild. So: a balanced feed or compost at planting, then a high-potash liquid every 1-2 weeks from first flower through harvest across the main season (spring through early autumn).

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

Follow the crop-feed label rate for mizuna — these are calibrated for hungry vegetables. Consistency through fruiting matters more than strength; erratic feeding causes problems like blossom-end rot.

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

Signs you are over-feeding mizuna

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

Vigorous dark-green leafy growth but few flowers or fruit (excess nitrogen).
Lush foliage hiding the crop; soft growth prone to pests and disease.
Salt crust on the soil and scorched leaf edges in containers.

Signs you are under-feeding mizuna

Pale, yellowing lower leaves and stunted growth.
Small fruit, poor set, and a quickly exhausted plant.
Blossom-end rot and weak cropping from erratic or insufficient feeding.

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

Flushing and leaching the salts

In containers, fertiliser salts build up fast — water mizuna thoroughly so excess drains from the base each time, and flush pots with plain water every few weeks to prevent a damaging salt build-up.

Organic vs synthetic feeds for mizuna

Organic options

Garden compost or well-rotted manure dug in before planting, plus a liquid comfrey or seaweed feed once fruiting starts. UK: comfrey feed or organic Tomorite; US: Espoma Tomato-tone or Neptune's Harvest. Builds soil and feeds in one.

Synthetic / liquid feeds

A balanced feed at planting then a high-potash tomato feed in fruiting — UK: Growmore at planting then Tomorite (Levington) or Phostrogen; US: a balanced 10-10-10 then Miracle-Gro Tomato or a bloom booster.

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 mizuna — frequently asked questions

What fertiliser does mizuna need?

Balanced (even N-P-K) at planting for roots and frame, then switch to a high-potassium ("high-potash") tomato-style feed once the first flowers open — potassium is what sizes and ripens fruit, not nitrogen. Mizuna feeds in two distinct phases — balanced to build the plant, then high-potassium the moment flowering starts to set and fill a heavy crop.

How often should I feed mizuna?

Light-to-moderate feeder. Compost-enriched soil usually meets its needs; for repeated cut-and-come-again harvests, a nitrogen-rich liquid feed after each cutting keeps regrowth fast and leaves tender and mild. Light-to-moderate feeder. Compost-enriched soil usually meets its needs; for repeated cut-and-come-again harvests, a nitrogen-rich liquid feed after each cutting keeps regrowth fast and leaves tender and mild. So: a balanced feed or compost at planting, then a high-potash liquid every 1-2 weeks from first flower through harvest across the main season (spring through early autumn).

What strength of feed for mizuna?

What does over-feeding mizuna look like?

Vigorous dark-green leafy growth but few flowers or fruit (excess nitrogen). Lush foliage hiding the crop; soft growth prone to pests and disease. Salt crust on the soil and scorched leaf edges in containers. Staying on a high-nitrogen feed once mizuna starts flowering is the classic error — you get a huge leafy plant and a disappointing crop. Switch to high-potash the moment flowers appear.

Should I flush the soil of mizuna?