A fast cool-season cover crop that puts on bulk top growth in six weeks and sends a taproot down through tight soil.
Brassica rapa subsp. oleifera · also called Turnip rape, Bird rape
Windows are counted from the average date of your last spring frost.
It fills the gaps between food crops: covering bare beds against erosion, smothering weeds, and returning a heavy load of soft green matter when turned under.
A little history. The same species as turnip and bok choy, selected for leaf and stem growth rather than a swollen root. Flowers are four-petaled and yellow, the standard cabbage-family pattern.
Sow seeds ½ inch (13 mm) deep, and aim for 2 inches (5 cm) between plants once thinned. Sow shallow and firm the surface. Keep the top half-inch moist until sprouts show; a dry crust stops the tiny seeds cold. Seedlings emerge in 4–10 days.
Water in at sowing, then only during a dry spell. Water when seedlings wilting by midday, or the top inch dry before the stand closes. Aim for about 1 inch per week including rain.
None on decent ground; feed once at sowing on worn-out soil. What to use: a light scatter of 5–5-5 organic fertilizer, about 1 lb per 100 sq ft, raked in.
Mow or shear at about 12 in if growth gets ahead of you and let it regrow. Cutting before bloom keeps stems soft and easy to turn under.
It's ready when ready to terminate when the top of each stalk shows its first open yellow flowers and stems still snap rather than bend. For the kitchen, cut young leaves with scissors while under 4 in. To end the stand, mow or shear at ground level at first bloom, then chop the tops and work them into the top 4–6 in of soil.
Young leaves keep 4–5 days in a bag in the crisper. Seed saved from dry pods stores in a sealed jar for about a year.
Sow a fresh patch every 3–4 weeks through cool weather to keep every emptied bed covered until you need it.
In mild winters plants survive and flower very early. Mow or turn them under before pods form, or you will weed volunteers all season.
Crimson Clover
Sown as a mix, clover banks nitrogen in its roots while mustard puts up the bulk top growth. Most of that nitrogen is released the following season as the clover roots break down, so the crop that follows benefits rather than the mustard itself.
Field Pea
Field pea climbs lightly through a mustard stand and stores nitrogen in root nodules. Turn both under together and the nitrogen becomes available as the residue rots, mostly in time for next season's planting.
Oats
Oats spread a dense fibrous mat in the top few inches while mustard drives a single taproot deeper, so the two share the soil instead of fighting for it. Both also winterkill in hard freezes, leaving an even mat to plant through.
Phacelia
Both flower early and shallow, and together they keep hoverflies, lacewings, and tiny parasitic wasps fed for weeks. Those insects then work the aphids on nearby food crops.
Apple
Left to flower in the strip between fruit trees, mustard feeds bees and predatory insects at a time when little else is open. Mow it before pods set so it does not seed itself through the orchard floor.
Beet
Chopped mustard residue releases sharp, short-lived compounds as it rots that can hold back the germination of small seeds. Beets are sown shallow and start slowly, so they are among the crops set back. Wait 2-3 weeks after turning mustard in before sowing beets.
Carrot
Fresh mustard residue often thins a carrot sowing, since carrot seed is tiny and takes two weeks to emerge even in clean ground. Let the chopped tops break down for 2-3 weeks, then rake and sow.
Lettuce, spinach, and other fine-seeded greens can germinate patchily in soil that still smells of freshly turned mustard. Transplants are unaffected — it is the germinating seed that suffers, so set out seedlings or wait out the residue.
Give the cabbage family 4 years away from this spot before any of its relatives return.
The tomato family, the pea and bean family or the carrot family thrive in this ground next season.
A giver: it takes little and leaves a heavy load of soft green matter that feeds soil life as it rots. Keep cabbage-family crops out of this bed for 4 years. Follow with tomato-family crops, peas and beans, or carrot-family crops, sowing small seeds 2-3 weeks after turning it under.
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