Vegetable · Brassicaceae
Mustard
Brassica juncea
Sow it in cool weather and up it comes, ready to serve as both a kitchen green and a gentle soil-cleaning cover crop.
Full sun
Every 3–7 days
45–84°F · 7–29°C
40–90 days
Overview
Mustard is one of those forgiving, fast brassicas that gives you two rewards from one easy plant. In the kitchen garden it hands you a peppery leaf crop and the seed for homemade condiment, ready to pick within weeks of sowing. Out on a plot it becomes one of the finest biofumigant cover crops you can grow, dug in green to freshen the soil before your next planting.
It sprouts from seed in cool weather and hurries to flower, opening bright yellow four-petaled blooms by spring or fall. Two species carry most of the work. Brown mustard, Brassica juncea, holds the strongest measure of the compounds behind biofumigation, while white mustard, Sinapis alba, gives us much of the condiment seed and smothers weeds beautifully in its own right.
If mustard has one small quirk, it's how keenly it wants to spread. Left to flower and pod, it scatters seed and returns as a weedy volunteer, so the one habit worth keeping is cutting it down at early flowering, before it has the chance to sow itself. Manage that and it rewards you with almost no fuss.
Care
The short version: give it full sun and cool weather, direct-sown into well-drained soil rich in organic matter. Keep it moist so it grows fast, expect very little fuss, and cut the stand down at early flowering before it sets seed.
Light
Mustard is happiest in full sun and grows fastest there, though it will forgive a little partial shade if that's what you have. The more light it soaks up, the more leaf you pick and the more biomass you bank for the soil.
Water
Keep the soil evenly moist and you'll get the quick, leafy growth mustard is grown for. Watering matters even more at termination, because once you chop a biofumigant stand and dig it in, water it in right away to drive the glucosinolate reaction and hold the gases in the ground.
Soil
Give it well-drained loam with plenty of organic matter and it settles in happily. Mustard is wonderfully easy about pH, taking anything from 5.5 to 8.5, and it's often grown to mop up leftover nitrogen and sulfur rather than to be fed at all.
Temperature
This is a cool-season plant, comfortable from about 45°F to 84°F (7°C to 29°C). Sow into soil in that range and it germinates fast, though a long spell of summer heat will push it to bolt and flower early, which is nothing to worry about.
Humidity
Ordinary outdoor humidity is all mustard asks, so there's no figure to fret over. Airflow matters more, since crowded damp stands can invite the cabbage-family diseases mustard already carries.
Feeding
Most of the time mustard needs no feeding at all, and in fact it's often grown precisely to scavenge the nutrients other crops leave behind. Work in a little nitrogen at planting only if your soil is genuinely poor.
Pruning
There's no ornamental pruning to do here, so you can set those worries aside. Instead you mow or chop the whole stand at early flowering to terminate it and release the biofumigant compounds before it sets seed.
Repotting
This one simply doesn't apply, which makes life easier. Mustard is a field and garden annual, direct-sown right where it grows and never potted up.
Size & spacing
Plants reach anywhere from 1 to 6 feet (30 to 180 cm) tall depending on type and season, spreading 6 to 18 inches (15 to 45 cm). Grown as a cover crop it's drilled or broadcast in a thick stand rather than spaced out one by one, so there's no fussy measuring.
When to plant
Mustard loves cool weather and has no fondness for summer heat, so timing is on your side. 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 quickly and flowers within weeks, so plan to cut it before it pods and you'll be right where you want to be.
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
Nearly every mustard hiccup comes down to one of two things: letting it go to seed, or hurrying the cover-crop steps that make biofumigation work. Find what matches below, act while it's early, and you'll have it back on track in no time.
Little mustard seedlings coming up all over the bed next year
Take heart, this is just self-sowing, and it only happens when a few plants are left to flower and form their pods before you cut them. Wild mustard is a known weed, so that dropped seed can settle in and greet you everywhere the next spring. You can stay ahead of it easily by cutting the stand at early flowering and gently pulling any stray seedlings while they are still tiny.
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 carrying over to your cole crops
Mustard belongs to the brassica family, so it shares its pests and soilborne diseases with cabbage, broccoli, kale, and radish. Grow it right before or right after those crops and you can build up flea beetles, aphids, and clubroot, which lingers in the soil and reaches every brassica it touches. Nothing here is hard to manage: pull and destroy anything that looks affected, and leave a comfortable multi-year gap before another cabbage-family crop returns to that ground.
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
Your mustard cover crop did not seem to clean up the soil
If a mustard cover crop leaves the soil looking untouched, don't worry, the fix is almost always in how you terminated it. The isothiocyanate gases doing the real work are quick to escape, so coarse residue or a slow till lets them slip away before they get a chance. Next time, chop the green growth nice and fine, work it into warm moist soil within about 20 minutes, water it in to hold the gases, and aim for early flowering when the glucosinolates are at their peak.
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
You can breathe easy here, because mustard is a safe edible crop, enjoyed as greens and ground into the familiar condiment. Nothing about it poisons people, pets, or animals. The only thing to keep an eye on is quantity, since the same heat that gives it flavor can mildly upset the gut if any animal really gorges on the raw leaves or seed.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats Safe
You can relax about your cat, because mustard is not poisonous to them and most simply won't bother with the sharp-tasting leaves. If one does chew a good mouthful of the pungent foliage, the most you'll likely see is a little drool or a passing tummy upset that clears up by itself.
Dogs Safe
There is nothing here that will poison a dog, so no need to fret. That peppery bite usually sends them off after one taste, and the worst a big mouthful of leaves tends to bring is a bit of gas or a soft stool that soon settles.
Horses Safe
Your horse is safe around mustard, though it isn't a feed you'd want them making a meal of. Should one graze a large helping of the seed or foliage it may get a mildly unsettled gut, so simply keep it as a small part of what they eat and all is well.
Rabbits Safe
Mustard greens make a perfectly fine treat for rabbits now and then. Just offer them slowly and in small amounts, the gentle way you would introduce any new green, and hold off on making them an everyday staple.
Livestock Safe
Mustard and other brassica forage graze safely, as long as your animals aren't left to gorge on them. Eaten in quantity the foliage and seed can mildly irritate the gut, so bring it in gradually and keep brassica to no more than about three quarters of the diet, and everyone stays comfortable.
Birds Safe
There is no poisoning risk to birds at all, and your chickens will gladly peck away at the leaves and seed. The greens add a welcome bit of variety to their run.
People Safe
Mustard greens and seed are everyday food, enjoyed raw, cooked, or ground into the familiar condiment. The only thing to mind is the heat, since a lot of the raw pungent leaf or seed can sting the mouth and gut, which is simply the same lively chemistry that gives mustard its kick.
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 you'll find for the garden and the field really comes down to a few species and a handful of named cover-crop blends. These are the ones worth getting to know.
Brassica juncea (brown / Indian / oriental mustard)
This is the high-glucosinolate biofumigant species, and cultivars like Caliente, Pacific Gold, and Kodiak are bred to load their tissue with the very compounds that knock back soil pests and weeds once you chop the plant and dig it in.
Sinapis alba (white / yellow mustard)
This is the white mustard grown both for condiment seed and for cover, and cultivars such as IdaGold make the glucosinolate sinalbin that gives it a real name for smothering weeds and building biomass.
'Caliente'
A high-glucosinolate Brassica juncea blend sold as a dedicated biofumigant cover crop, and it throws up heavy biomass for the chop-and-incorporate green manure that does the soil cleaning.
How to propagate
There's just one way to grow mustard, straight from seed, and you'll be glad to hear it could hardly be simpler.
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.
You'll find mustard about as easy as growing gets, since it comes from seed only and grows fast. Direct-sow it in cool weather, either 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. The seedlings break ground in a few days and run to flowering and peak biomass in roughly 6 to 12 weeks depending on the season, so cut the stand at early flowering, before it sets its own seed and leaves you volunteers to tidy up later.
Myths
Mustard cover crops fight weeds and soil pests just by shading and crowding them out like any thick cover crop.
Here is the lovely part: mustard is a true biofumigant, which is something more than simple shade. Its tissues are packed with glucosinolates, and when the chopped plant gets wet the enzyme myrosinase turns them into isothiocyanate gases close to the active ingredient in synthetic soil fumigants like metam sodium. Those gases knock back soilborne pathogens, nematodes, and weed seeds, but only if you chop the residue fine, dig it in at once, and keep the warm soil moist, since skip that and the volatile compounds simply drift off.