Leaf Mustard Growing Calendar: What to Do Through the Year

The shape of the year

Leaf mustard is a cool-season crop with a short life and no tolerance for long warm days. That single fact organizes the whole year: you sow into cooling conditions whenever you can, you sow into warming conditions only with the intention of picking fast and small, and you leave high summer to something else entirely.

The most productive plan for most gardens is a small spring sowing for baby leaf, nothing at all through the hottest eight to ten weeks, then a substantial sowing as the heat breaks that you grow out into full heads and harvest across autumn and into winter. In a mild climate that autumn sowing keeps producing until it flowers the following spring.

Succession is what makes the crop useful rather than a glut. Sow a short row every two to three weeks within each window rather than everything at once, and you will pick continuously instead of facing thirty plants that all bolt in the same fortnight.

The spring crop is a race

A spring sowing has a fixed deadline that has nothing to do with how the plants look. Lengthening days combined with rising temperatures will send leaf mustard to flower regardless of how well it is growing, and the plant will often bolt at half its potential size. Plan for baby leaf, get two or three cuts, and treat anything more as a bonus rather than budgeting for whole heads.

Everything that keeps the bed cool buys time. Sow in a position that gets afternoon shade, mulch as soon as the seedlings are thinned, water deeply and consistently, and shade the row with thirty percent cloth once daytime temperatures pass 75F (24C). Between them these steps commonly add ten to fourteen days of picking.

When the crowns start to elongate, stop trying to save the crop and switch to using it. Take everything usable within the week, then cut the flower stems with tight buds as a second harvest, and clear the bed before the pods form unless you actively want volunteers.

1. Sow small and often A three-foot (1 m) row every two weeks from the first workable soil until six weeks before your summer heat arrives. Any single sowing will be usable for a shorter window than you expect.
2. Cover at sowing, not later Row cover goes on before emergence and stays on. Spring seedlings are hit hardest by flea beetles because the plants are small and the beetles are hungry after winter.
3. Cut early rather than waiting for size Leaves picked at four inches (10 cm) in spring are worth more than the bigger ones you might get by waiting two more weeks and losing the lot to bolting.

The late-summer sowing is the real crop

Sowing as summer heat breaks, giving the plants eight to ten weeks of growth before your first hard frost, produces the crop this vegetable is actually for. Days shorten, nights cool, there is no bolting pressure, and the plants put everything into broad heavy leaves with thick pale midribs. Growth accelerates through early autumn and then slows to a steady trickle you can pick from all winter in a mild climate.

Space these plants properly at twelve to eighteen inches (30 to 45 cm), because they will get far larger than a spring crop ever does. Feed once when they are a third grown, mulch to hold moisture, and start taking outer leaves as soon as the plants have eight or nine of them. Regular picking keeps the center productive right through the cold months.

Mature plants take frost down to about 20F (minus 7C) without protection and the cold improves them, sweetening the midribs and softening the pungency. Below that, a cloche or low tunnel keeps the crop going. The plants will eventually bolt in spring as the days lengthen, which is the natural end of that sowing and the point to take the flower stems and clear the bed.

1. Check soil temperature before sowing Wait until the top two inches (5 cm) are back below 85F (29C). Sowing into hotter soil gives patchy germination and seedlings that carry a bolting tendency with them.
2. Thin ruthlessly to final spacing Crowded autumn plants stay small, hold damp air in the crown and rot at the base through winter. Eat the thinnings as baby leaf and do not compromise on the final spacing.
3. Prepare for winter before it arrives Pull mulch back an inch (2.5 cm) from every stem, clear yellowing lower leaves, and have hoops and cover ready to go on rather than scrambling the night of the first hard freeze.

Keep a note of your first and last frost dates, the soil temperature on each sowing day, and the date each sowing bolted. Two seasons of those numbers will tell you your own optimum sowing dates far more accurately than any general guidance can.

What to record, and the self-seeding decision

The records worth keeping on this crop are short and specific. Note the sowing date and soil temperature; the bed and which end of it you used; the date of emergence and of first flea beetle damage; the date of the first cut and how many cuts each sowing produced; the date the crowns began to elongate; and a one-word verdict on flavor at each harvest, mild through to fierce. Add the weather in the week before any cut that tasted unexpectedly hot.

Read together, those notes answer the questions that actually matter next year: how early you can safely sow, how late in summer you must wait, which bed gives mild leaves and which gives hot ones, and how many plants you need for the amount you actually eat. They also let you separate a genuinely poor season from a sowing that simply went in two weeks too late.

The last decision each year is about volunteers. Leaf mustard self-seeds very freely, and a single plant left to ripen pods will scatter hundreds of seeds that come up in the following seasons wherever the soil is disturbed. Volunteers are perfectly good eating and cost nothing, but they appear in the wrong beds and confuse your rotation. If you want them, leave one plant and mark where it stood. If you do not, clear every plant while the pods are still green, and pull volunteer seedlings as weeds for the next two years until the seed bank is spent.