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How to Grow Mustard for Leaves, Seed or Green Manure

Mustard germinates in days and crops in 40. Spacing and timing for salad leaves, seed harvest and a soil-conditioning cover crop.

By Salma 3 min read Save to Pinterest — opens Pinterest in a new tab
A head of yellow mustard flowers with seed pods forming below
Photo: Uschi_Du, Pixabay Content License, via Pixabay
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Mustard is the fastest useful thing in most vegetable gardens: germinating in under a week, leaves in a month, and useful as a green manure between crops.

Sowing

purposespacingsowing depthtiming
Baby leaf2–3 in1/4–1/2 inEarly spring, late summer, every 2–3 weeks
Full-size leaf6–9 in1/2 inEarly spring, late summer
Seed12 in1/2 inSpring, for autumn harvest
Green manureBroadcast thicklyRaked inAfter a crop comes out, late summer

Rows nine to twelve inches apart. Thin in two stages and eat the thinnings.

Growing on

  • Full sun to light shade; afternoon shade helps in heat
  • Consistent moisture. Drying out triggers bolting and bitterness
  • Fertile soil — it is a leafy brassica and responds to compost
  • Watch for flea beetle, which shot-holes the leaves; row cover is the answer
  • Cabbage white caterpillars eat it too, despite the heat in the leaves

Succession beats quantity

A short row every two to three weeks gives continuous tender leaves. One big sowing produces a glut that bolts all at once.

Harvesting leaves

  • Baby leaf: scissor-cut an inch above soil level, two or three cuts per sowing
  • Full-size: take outer leaves at the base, leaving the growing point — the same method as lettuce
  • Flavour: mildest when young and cool-grown; heat and age both increase the pungency
  • Flower buds and shoots are also edible, like sprouting broccoli, once it starts to bolt

Harvesting seed

  1. Watch the lower pods — pale brown and rattling
  2. Cut whole stems before the pods split
  3. Head-down in a paper bag or upturned bucket, somewhere dry and airy, for one to two weeks
  4. Thresh by rubbing the pods between your hands
  5. Winnow the chaff off in a light breeze
  6. Store dry and airtight

Mustard shatters readily and self-seeds freely. Expect volunteers next year wherever you grew it.

As a green manure

  • Sow thickly after an early crop comes out
  • Cut and dig in while green, at six to eight weeks, before flowering
  • Biofumigation: chopping the green tissue releases glucosinolates that suppress some soil pests and nematodes
  • Rotation caution: it is a brassica. Do not use it before cabbages, or where clubroot is present

Common questions

How long does mustard take to grow?

Baby leaves in three to four weeks, full-size leaves in forty to fifty days, and seed in about ninety to a hundred days from sowing. It germinates in three to seven days in warm soil, which makes it one of the fastest things in a vegetable garden and a good crop for impatient gardeners or children. As a green manure it is dug in or cut down after six to eight weeks, well before it flowers.

How far apart should mustard be spaced?

Six to nine inches for full-size leaf plants, two to three inches for a cut-and-come-again baby leaf row, and twelve inches for plants grown on for seed. Thinning matters more than it looks: crowded mustard bolts earlier and produces smaller, tougher leaves. Sow thinly in rows nine to twelve inches apart and thin in two stages, eating the thinnings as salad.

Does mustard bolt in hot weather?

Quickly, which is the main thing to plan around. Mustard is a cool-season crop that runs to seed in long days and heat, and bolted leaves turn bitter and tough. Sow in early spring and again in late summer for autumn harvest, skip midsummer entirely in warm climates, keep the soil consistently moist, and provide afternoon shade if you must grow it in heat. If you want seed, bolting is the goal rather than the problem.

When do you harvest mustard seed?

When the lower pods have turned pale brown and rattle, but before they split and shed. Cut whole stems, put them head-down in a paper bag or upturned bucket and let them finish drying for one to two weeks, then thresh by rubbing the pods and winnow the chaff off. Leaving the plant until every pod is dry on the stem means losing most of the crop — mustard pods shatter readily and self-seed enthusiastically.

Is mustard a good cover crop?

Yes, and it does two jobs. It produces a lot of biomass fast, so it adds organic matter and smothers weeds, and as a brassica it releases glucosinolates when chopped and incorporated, which suppresses some soil pests and nematodes — the biofumigation effect. Sow it in late summer after a crop comes out, and cut and dig it in while green, before flowering. The caution is rotation: it is a brassica, so do not use it where you plan cabbages, or where clubroot is present.

What is the difference between mustard greens and mustard seed varieties?

Breeding priority, mostly. Leaf varieties such as Green Wave, Red Giant and Mizuna are selected for tender flavourful foliage and are slower to bolt; seed types such as brown or black mustard are grown for the pods and bolt readily. You can harvest seed from a leaf variety and leaves from a seed variety — both work, just less well than the dedicated type. For green manure, buy the cheap bulk agricultural seed rather than named varieties.

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