When and How to Harvest Leaf Mustard: Baby Leaf or Whole Heads

Size tells you what the leaf is good for

There is no single point of ripeness. Leaf mustard is usable from the moment the leaves are big enough to bother with until the flower stem is a foot (30 cm) tall, and the flavor and texture change continuously across that range. Pick according to what you want to do with it rather than waiting for the plant to signal anything.

Small leaves of three to four inches (8 to 10 cm) are mild enough for salad, with a mustard bite but no bitterness. At six to eight inches (15 to 20 cm) the leaf has enough substance to hold up to heat and the midrib is still tender, which is the sweet spot for cooking. Beyond ten inches (25 cm) the blade gets tough and the flavor gets assertive, but the thick pale midribs become the best part of the plant and can be stripped out and cooked separately.

A full head, meaning the whole plant lifted at sixty to eighty days, can weigh two to four pounds (1 to 2 kg) with a dense cluster of overlapping broad leaves. Lift it by cutting through the stem at soil level with a knife rather than pulling, which brings up soil and breaks the outer leaves.

The weather in the week before a cut matters more than the calendar

Two plants sown on the same day can taste completely different depending on what the weather did just before you cut them. Heat, wind and dry soil all raise pungency within days, while a cool, damp, overcast spell lowers it just as fast. If a cut tastes far hotter than you expected, the cause is almost always the preceding week rather than the age of the plant.

Cool weather does the opposite and improves the crop noticeably. After a couple of light frosts the midribs sweeten, the harshness drops away, and leaves that were borderline raw a fortnight earlier become pleasant. This is the main argument for treating the autumn sowing as the real crop and the spring one as a bonus.

Time of day helps at the margins. Cut in the early morning while the leaves are turgid and cool, and the greens keep two or three days longer in the fridge than the same leaves cut in the afternoon heat. Plunge cut leaves into cold water for a few minutes, spin them dry, and store them loosely bagged.

Cut so the plant keeps producing

Leaf mustard regrows readily from the crown, so how you cut determines how many harvests you get. Baby leaf sown thickly can be sheared across the block about an inch and a half (4 cm) above the soil, leaving the growing points intact, and will come back for two or three more cuts at two to three week intervals before the regrowth turns coarse.

Full-size plants are better picked leaf by leaf. Take the outer two or three leaves from each plant, snapping or cutting them off flush with the stem, and leave at least six or seven leaves in the center so the plant keeps its engine. Worked this way a single autumn plant will supply picking for two months or more.

Taking the whole head is the end of that plant, so save it for when the weather is about to turn hard or the plant is beginning to bolt. Cut at soil level and leave the roots in place to break down rather than pulling and disturbing the bed.

1. Shear baby leaf above the crowns Gather a handful, cut straight across at 1.5 in (4 cm), and do not go below the lowest visible growing points. Cutting too low gives no regrowth and leaves a bare patch in the block.
2. Strip midribs from oversized leaves On leaves over 10 in (25 cm), run a knife down each side of the pale midrib. Cook the ribs like a stem vegetable and treat the blade as a separate green with a shorter cooking time.
3. Clear the plant before the flower stem hardens Once a plant is elongating, take everything usable within a week. The leaves get progressively tougher and hotter each day after that, and a bolting plant will not go back to making flat leaves.

Note the date of the first cut, the date the flavor got noticeably hotter, and how many cuts each sowing gave you before it ran out. Those three numbers tell you next year whether to sow earlier, sow more often, or simply sow more at once.

Harvesting after the plant has bolted

A bolted plant is not wasted. The flower stems, taken while the buds are still tight and the stem snaps cleanly when bent, are one of the best things the plant produces: sweeter than the leaves, with a texture like sprouting broccoli. Cut the top six inches (15 cm) of stem and the plant will usually push out a second flush of smaller side shoots.

Once the flowers open, quality drops away fast and the plant switches its energy to seed. At that point decide deliberately: pull it and clear the bed, or leave one or two plants to ripen pods. Seed is mature when the pods turn pale brown and rattle, and the plant will self-seed generously if you let the pods split in place, which is a convenience if you want a volunteer patch and a nuisance if you do not.