How to Grow Mustard Greens from Seed (Brassica juncea)

Mustard greens are the crop that repays a late sowing better than almost anything else in the vegetable garden. Sow Brassica juncea in April and you will get a fortnight of leaves before the plants bolt and turn ferociously hot; sow the same packet in the second half of August and you will be picking mild, crisp, nutty-peppery leaves into November, from plants that shrug off the first frosts and actually taste sweeter for them. They germinate in three or four days, tolerate poor soil, and give you two entirely different crops depending on how thickly you sow. This guide covers the whole cycle — when to sow, how to keep flea beetle off, how to harvest as baby leaf or full-sized plants, and how to use leaves that range from salad-mild to horseradish-fierce.

• Botanical name Brassica juncea — fast annual leaf crop, Brassicaceae (cabbage family)
• Sow late July–mid September outdoors for the best crop; March–April for a quick spring picking
• Harvest baby leaf from 21–30 days; full-sized plants from 45–60 days
• Position sun or light shade, moisture-retentive soil — never let it dry out

Why grow mustard greens

Speed is the first reason. Three weeks from sowing to a bowl of salad leaves is quicker than almost any other outdoor vegetable, which makes mustard the perfect crop to slot into ground that has just been cleared of beans, garlic or early potatoes. The second reason is the flavour, which is genuinely different from anything else in the salad bowl: green-tea bitterness at the front, a nutty middle, and a wasabi-like heat at the finish that hits the nose rather than the tongue.

The third reason is the range. Under the name Brassica juncea sits a whole spectrum of plants — smooth, upright amsoi for the wok, huge crimson-veined Red Giant leaves for the salad bowl, and lacy Red Frills that are as ornamental as they are edible. Browse the whole family under mustard greens, or by botanical name at Brassica juncea. New to vegetables from seed? Our beginner's guide to growing vegetables from seed covers the groundwork.

When to sow mustard greens — and why autumn beats spring

This is the single thing that separates a good crop from a disappointing one. Mustard greens are day-length sensitive and heat sensitive: as days lengthen and temperatures climb past roughly 24 °C, the plant reads the conditions as a signal to run to flower. Bolting is not just a loss of leaves — it changes the chemistry, concentrating the pungent compounds so the remaining leaves become genuinely unpleasant to eat raw. A spring sowing is therefore always a race against the plant's own biology.

Sow from late July to mid September and everything works in your favour. Soil is warm enough for germination in three days, day length is shortening rather than lengthening, and the cooler nights of September and October slow the plants down so the leaves stay thick and sweet. A light frost improves them further, because the plant converts stored starch to sugars as a natural antifreeze. See what else can go in alongside them in what to sow in August, and check the timings for every crop in our vegetable sowing calendar. Sowing from an old packet? Test it first using the method in our guide to how long seeds last.

How to sow mustard greens, step by step

1. Decide which crop you want first Baby leaf and full-sized plants are the same seed sown at different densities. For cut-and-come-again salad, broadcast thickly in a band 10 cm wide. For big plants, sow in rows 30 cm apart and thin to 25–30 cm. Choose before you open the packet — you cannot easily convert one into the other.
2. Prepare firm, moisture-retentive ground Mustard bolts under drought stress as readily as under heat. Rake to a fine tilth and work in compost first, following our soil preparation guide. Avoid ground that grew cabbage, kale or turnips last year — mustard is a brassica and shares their soil-borne diseases.
3. Sow shallowly and water the drill, not the seed Cover with just 5–10 mm of soil. Water the bottom of the drill before sowing rather than sprinkling afterwards — it keeps the seed in place and puts moisture where the roots will go. Full method in our direct sowing guide.
4. Cover with fleece or fine mesh from day one This is the most important step, and it must go on before the seedlings appear, not after you spot damage. See the pest section below for why.
5. Sow again every two to three weeks Mustard is short-lived by design. A short row every fortnight until mid September gives continuous picking rather than one glut — the approach set out in our guide to succession sowing. Nothing coming up? Work through our germination troubleshooting guide.

Mustard greens, mizuna, or mustard for green manure?

Three quite different things are sold as "mustard", and confusing them wastes a season. The two edible leaf crops below are close cousins; the third — white mustard, Sinapis alba — is a different genus grown to be dug in, not eaten as a leaf vegetable.

White mustard (Sinapis alba) is the fast-growing cover crop sown on bare beds in autumn — useful, but a brassica, so it counts in your rotation. Our guide to green manures explains where it fits. The same seed sprouted indoors gives the peppery shoots in our microgreens and sprouts guide — browse those under sprouting seeds.

Caring for mustard greens

Water is the whole job. Mustard has a shallow root system and reacts to dry soil by bolting, so aim for steady moisture rather than an occasional soaking — the principles in our watering guide apply, but with mustard err on the side of more frequent. A mulch of compost between the rows holds moisture and keeps soil off the lower leaves.

Flea beetle is the pest that decides whether your crop looks good or looks like a colander. The adults chew hundreds of tiny round holes in young brassica leaves and are at their worst in warm, dry weather from May to early August. Two things beat them, and both are about timing rather than treatment: sow after the middle of August, when beetle numbers are falling, and cover the bed with fine insect mesh from the moment you sow so the beetles never reach the seedlings. Established plants with big leaves shrug off the damage; it is the cotyledon stage that matters. Slugs are the other autumn nuisance — our guide to common garden pests covers both. Mustard also earns its place in a mixed bed as a decoy crop for flea beetle near more precious brassicas, one of the tactics in our guide to companion planting. Growing in pots or a raised bed works well too, since you control the compost and the watering: see container growing from seed and raised bed gardening.

Harvesting and using mustard greens

For baby leaf, cut the whole band with scissors about 3 cm above soil level once the leaves reach 8–10 cm. Leave the growing point intact and the plants will regrow for two or three more cuts. For full-sized plants, pick outer leaves from the bottom of each rosette and let the centre keep producing — a single autumn plant can yield for two months this way. General principles are in our guide to harvesting and storing produce.

The heat is worth understanding, because you control it. Mustard leaves store a compound called sinigrin separately from the enzyme that activates it; the fierce, sinus-clearing flavour is only produced when you rupture the cells. So a whole young leaf in a sandwich is mild, the same leaf finely shredded is sharp, and either one dropped into a hot pan for 90 seconds becomes as gentle as spinach, because heat destroys the enzyme. Cook the older, coarser leaves and save the small ones for salad. If you leave a plant to flower, the yellow blooms are edible, the bees will find them, and the seed pods that follow can be collected using the methods in our guide to seed saving.

Common mustard greens mistakes

• Sowing in late spring and blaming the seed — heat and lengthening days cause bolting. Move the sowing to August and the same packet performs completely differently.
• Putting the mesh on after you see holes — flea beetle damage happens in the first fortnight. Cover at sowing or not at all.
• Letting the bed dry out — drought stress triggers bolting just as reliably as heat does.
• Sowing thickly and then expecting big plants — crowded mustard stays as baby leaf. Thin to 25 cm if you want full rosettes.
• Following cabbage or kale in the same bed — mustard is a brassica and shares clubroot. Rotate it with roots, legumes or salads.
• Judging the flavour from one raw leaf — taste it cooked as well. The same plant tastes like two different vegetables.
• Sowing the whole packet at once — a short row every fortnight is far more useful than one enormous glut in October.

Frequently asked questions

Is mustard greens the same as amsoi?
Amsoi is one form of Brassica juncea — an upright, smooth-leaved Asian type grown mainly for stir-frying, with a milder heat than the frilled or red-leaved mustards. Botanically it sits in the same species, so sowing, spacing and timing are identical.

Will mustard greens survive winter outdoors?
They take light frost well and often improve for it, holding in reasonable condition to about −5 °C. Below that the leaves collapse. Under a cloche, cold frame or thick fleece in a sheltered spot, an August sowing will usually crop into December or January.

Why are my mustard greens so hot?
Three usual causes: the plant has bolted, it has been drought-stressed, or the leaves are simply old. Pick younger, water more consistently, and cook the coarse leaves rather than eating them raw.

Can I grow mustard greens indoors on a windowsill?
For baby leaf and microgreens, yes — a shallow tray of compost on a bright sill gives a cut in three weeks. Full-sized plants need more root run and better light than most windowsills provide, so grow those outdoors or in a large pot.

Few crops give this much back from a fortnight of your attention. Give mustard a cleared bed in late August, keep it damp and covered, and it will feed you salads long after the tomatoes have gone. Sow it alongside lettuce, spinach, rocket, corn salad, radish, chard and kale; browse our organic seeds or read heirloom vs F1 vs organic if you are choosing between types. See everything else that can go in now in sow in August and sow in September, and if you are thinking about how the garden will look once the vegetable beds empty, our guide to growing ornamental grasses from seed covers the plants that carry a border through winter. Browse all our vegetable seeds, our full seed range, or dig into the rest of our growing guides.