Vegetable · Brassicaceae
Mustard
Brassica juncea
Sown in the cool of the season, it rises fast to earn a place as both a kitchen green and a soil-restoring cover crop.
Full sun
Every 3–7 days
45–84°F · 7–29°C
40–90 days
Overview
Mustard has a way of fitting two roles into one corner of a garden. In the kitchen plot it is a peppery leaf crop and the source of homemade condiment seed, ready for the table within weeks of sowing, a quick reward that slots neatly into the rhythm of a growing season. Give it a wider bed and it becomes one of the finest biofumigant cover crops to be had, turned in green to leave the ground fresh for whatever follows.
Sown in cool weather, it hurries to flower and lifts a wash of bright yellow four-petaled blooms across the plot by spring or fall, a cheerful interlude between crops. Two species carry the work. Brown mustard, Brassica juncea, holds the strongest measure of the compounds behind biofumigation, while white mustard, Sinapis alba, supplies much of the condiment seed and smothers weeds handsomely on its own.
Its one real caveat is a fondness for spreading. Left to flower and pod, it sows itself and returns as a weedy volunteer that unsettles a well-kept garden, so the habit worth keeping is cutting it down at early flowering, before it can seed the ground around it.
Care
The short version: give it a full-sun spot and cool weather, direct-sown into well-drained soil rich in organic matter. Keep it moist for fast growth, expect little fuss in the routine, and cut the stand down at early flowering before it sets seed.
Light
Mustard belongs in a full-sun part of the garden, where it grows fastest, though it accepts a little partial shade if the spot calls for it. The more light it takes in, the more leaf it offers and the more biomass it banks for the soil.
Water
Keep the soil evenly moist and mustard rewards you with the quick, leafy growth it is grown for. Watering counts for even more at termination: once a biofumigant stand is chopped and turned in, water it in without delay to drive the glucosinolate reaction and hold the gases in the ground.
Soil
Set it in well-drained loam generous with organic matter. Mustard is remarkably relaxed about pH, taking anything from 5.5 to 8.5, and it often earns its place by mopping up leftover nitrogen and sulfur rather than asking to be fed.
Temperature
This is a cool-season plant, at ease from about 45°F to 84°F (7°C to 29°C). Sow into soil in that range and it germinates fast, while a long stretch of summer heat nudges it to bolt and flower early.
Humidity
Ordinary outdoor air is all mustard asks, so there is no figure to chase in the routine. Airflow matters more, since a crowded, damp stand invites the cabbage-family diseases the crop already carries.
Feeding
Most seasons mustard needs no feeding at all, and it is often grown for the very purpose of scavenging the nutrients earlier crops left behind. Work in a little nitrogen at planting only where the soil is genuinely poor.
Pruning
There is no ornamental pruning to fold into the routine. The task that matters is to mow or chop the whole stand at early flowering, ending it and releasing the biofumigant compounds before it seeds.
Repotting
This one falls away entirely. Mustard is a field and garden annual, direct-sown where it grows and never brought to a pot.
Size & spacing
Depending on type and season, plants stand 1 to 6 feet (30 to 180 cm) tall and spread 6 to 18 inches (15 to 45 cm). As a cover crop it is drilled or broadcast into a thick sweep across the bed rather than set out as individuals.
When to plant
Mustard keeps to the cool of the year and has no appetite for summer heat. Direct-sow it in early spring the moment the soil works, or again in late summer to early fall about four weeks before the first hard freeze. It grows fast and flowers within weeks, so let its harvest and termination fall before it pods.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Not typically started indoors; direct-sow in the field/garden.
- Plant: Direct-sow in cool weather - early spring as soil works, or late summer/early fall about 4 weeks before the first hard freeze, into soil 45-85 degrees F.
- Harvest: Bright yellow four-petaled flowers in spring or fall; for biofumigation terminate at early flowering before seed set.
Hardiness
USDA hardiness zones: 3–11
Temperature: down to -40°C
Troubleshooting
Most of what goes awry with mustard comes back to two habits: letting it run to seed, or hurrying the cover-crop steps that make biofumigation work. Match what the garden is showing below, then act early while it still counts.
Volunteer mustard turning up across the plot next season
The culprit is self-sowing, the quiet result of letting a few plants flower and fill their pods before they come down. Feral mustard counts as a weed, so the seed that scatters can reappear across the whole plot the following year, unsettling an otherwise tidy garden. Bring the stand down at early flowering, mow or chop it in, and lift the odd stray seedling while it is still small.
Fix:
- Mow, chop, or till in volunteers before they flower
- Cultivate or hand-pull seedlings while small
- Avoid letting any plants reach mature pods
Cabbage-family pests and diseases following on to your cole crops
Mustard belongs to the brassica family, which means it keeps the same company of pests and soil diseases as cabbage, broccoli, kale, and radish. Set it just before or after those crops in the same beds and the trouble accumulates, from flea beetles and aphids to clubroot, which settles into the soil and reaches every brassica nearby. Clear away and destroy anything affected, and plan a generous multi-year pause before another cabbage-family crop takes that ground again.
Fix:
- Remove and destroy affected plants
- Do not follow mustard immediately with cabbage, broccoli, kale, radish, or other brassicas
- Rotate to a non-brassica crop
A biofumigant mustard that never delivered for the soil
When a mustard cover crop leaves the soil no better than before, the answer nearly always sits in how the stand was terminated. The isothiocyanate gases behind the whole benefit are fleeting, so coarse residue or an unhurried till lets them slip away before they act. Chop the green growth finely, fold it into warm, moist soil within about 20 minutes, water it in to keep the gases below ground, and time the work to early flowering, when the glucosinolates reach their height.
Fix:
- Chop the green biomass finely with a flail mower
- Incorporate (till in) immediately, within about 20 minutes
- Irrigate/water in right after to seal in the gases
- Time termination to early flowering
Toxicity
The reassurance is easy to give: mustard is a safe edible crop, enjoyed as greens and ground into the familiar condiment. Nothing about it poisons people, pets, or the animals that share a garden. The only note to keep is quantity, since the very heat that gives it character can mildly irritate the gut when any animal overindulges in the raw leaves or seed.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats Safe
A household cat has nothing to fear from mustard, and the sharp leaves rarely tempt one in the first place. Should a curious cat sample a good deal of the pungent foliage, a little drool or a passing stomach upset is the worst of it, and it settles on its own.
Dogs Safe
Mustard holds nothing toxic for a dog wandering the garden. The peppery taste tends to end the experiment after a mouthful, and a larger helping of leaves usually leads to no more than a little gas or a soft stool.
Horses Safe
Horses are safe in the company of mustard, though it is hardly a feed to base a paddock on. A horse that grazes a large amount of the seed or foliage may end up with a mildly unsettled gut, so keep it a modest part of the daily ration.
Rabbits Safe
Mustard greens suit rabbits nicely as an occasional leaf on the menu. Offer them gradually and in small amounts, the way any new green is best introduced, rather than as a daily fixture.
Livestock Safe
Mustard and other brassica forage graze safely across a pasture, provided animals are not left to overindulge. Eaten in quantity, the foliage and seed can mildly irritate the gut, so bring it in gradually and hold brassica to no more than about three quarters of the diet.
Birds Safe
For birds there is no risk of poisoning here, and hens will happily work over the leaves and seed. The greens lend a welcome note of variety to the run.
People Safe
At the table, mustard greens and seed are everyday fare, taken raw, cooked, or ground into the familiar condiment. The single caveat is the heat, since a large helping of the raw pungent leaf or seed can sting the mouth and gut, the very chemistry that gives mustard its character.
Treat normal mustard greens and seed as ordinary food for people. The concern is large-quantity exposure: dogs or cats nibbling a lot of the pungent leaves or seed may get GI/mouth irritation, and livestock grazing large amounts of mustard or other brassica forage can develop bloat, digestive upset, hemolytic anemia, goiter/hypothyroidism, or brassica poisoning. Wear gloves and avoid breathing dust when chopping large amounts of biofumigant mustard, as the isothiocyanate vapors are pungent and irritating.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
United Kingdom
Animal PoisonLine: 01202 509000 (fee applies)
Australia
Animal Poisons Helpline: 1300 869 738
Varieties
The mustard offered for garden and field comes down to a few species and a handful of named cover-crop blends. These are the ones worth knowing by name.
Brassica juncea (brown / Indian / oriental mustard)
This is the high-glucosinolate biofumigant species, its cultivars like Caliente, Pacific Gold, and Kodiak bred to fill their tissue with the compounds that clear soil pests and weeds once the plant is chopped and turned in.
Sinapis alba (white / yellow mustard)
This white mustard earns its place both for condiment seed and for cover, and cultivars such as IdaGold carry the glucosinolate sinalbin that gives it its name for smothering weeds and raising biomass.
'Caliente'
A high-glucosinolate Brassica juncea blend sold as a dedicated biofumigant cover crop, prized for the generous biomass it raises for the chop-and-incorporate green manure that refreshes the soil.
How to propagate
Mustard is grown one way alone, straight from seed, and few crops slip so easily into a season's plans.
SeedEasy
Direct-sow in cool weather: early spring or late summer/early fall, into soil about 45-85 degrees F. · Germinates in a few days and grows fast, reaching flowering and peak biomass in roughly 6-12 weeks depending on season.
Mustard comes from seed and seed alone, and it settles in with an ease that suits any busy season. Direct-sow in cool weather, whether in early spring or in late summer to early fall, into soil around 45°F to 85°F (7°C to 29°C). Drill it about 5 to 12 pounds an acre at a quarter to three quarters of an inch deep, or broadcast 10 to 15 pounds an acre for a fuller sweep. Seedlings appear within days and reach flowering and peak biomass in roughly 6 to 12 weeks by season, so bring the stand down at early flowering before it seeds itself and leaves you volunteers to manage.
Myths
Mustard cover crops fight weeds and soil pests just by shading and crowding them out like any thick cover crop.
Mustard earns its keep as a genuine biofumigant, something well beyond the shade of a leafy canopy. Its tissues hold glucosinolates, and once the chopped plant meets water the enzyme myrosinase converts them into isothiocyanate gases close kin to the active ingredient in synthetic soil fumigants such as metam sodium. Those gases see off soilborne pathogens, nematodes, and weed seeds, though the benefit lands only if the residue is chopped fine, turned in at once, and the warm soil kept moist, since the volatile compounds otherwise drift away.