Cabbage

Start spring cabbage indoors, four to six weeks before set-out

Sow seed a quarter inch deep in flats and grow them on at normal room temperature, around 60 to 70 degrees. Count back four to six weeks from the date you intend to set plants out. A transplant is ready when it has four to six mature leaves and a root system that holds the plug together. Cabbage needs a long cool run to fill a head, and warm rooms above the mid-70s push weak, stretched seedlings that never size up. Starting on a countdown from your own set-out date is what keeps the head forming before summer heat arrives.

Sow the fall crop in midsummer for a cool-weather finish

Start seed about three weeks before you plan to set the plants out, counting back so the heads mature as weather cools. Keep the flats and the new transplants well watered - this is the hard part of a fall crop. A fall crop heads into falling temperatures instead of away from them, which is the weather cabbage actually wants. Watering is the difficulty: seed and young transplants have to get established in summer heat before the cool run they were sown for arrives.

Set out hardened transplants ahead of the last frost

Harden the plants off outdoors over one to two weeks, then set them 12 to 18 inches apart in rows 24 to 36 inches apart. Cabbage is hardy enough to go out two to three weeks before your last frost date and is not seriously damaged by temperatures down to 25 degrees. Cabbage heads best in cool weather, so the earlier it establishes the better it fills. Its frost hardiness is what buys those extra weeks - the plant is working while tender crops are still waiting.

Even moisture at the soil line, never overhead

Give one to two inches of water a week, applied deeply and infrequently, and aim for steady soil moisture rather than swings. Water at the ground with drip or a soaker hose instead of a sprinkler. A head that dries out and then gets a heavy drink takes up water faster than the wrapped leaves can stretch, and it splits. Overhead water does a second kind of damage - it splashes the black rot bacterium from leaf to leaf, and black rot has no cure once it is in the plant.

Side-dress nitrogen once, then stop before heads form

About four weeks after transplanting, band roughly half a cup of 21-0-0 per 10 feet of row about six inches out from the plants, scratch it in, and water it down. Do not add more nitrogen once heads begin to firm up. Cabbage builds its frame of outer leaves first and the head is filled from what those leaves make, so nitrogen pays early and only early. Nitrogen after heading pushes soft, loose growth into a head that is already tight, which is what makes heads split.

Check leaf undersides weekly for caterpillar eggs

Walk the planting once a week and turn over the lower leaves. Look for small yellow-orange eggs laid singly and for green caterpillars up to an inch long - the imported cabbageworm has a faint yellow stripe down its back, the looper arches its back as it crawls. Check even where you see no chewing yet. Caterpillar control works on small larvae and fails on big ones, so finding eggs before they hatch is the whole point of the walk. Waiting for holes means waiting until the larvae are past the stage where anything kills them cleanly, and by heading their droppings contaminate the head itself.

Bt on small cabbageworms as soon as you find them

When scouting turns up small larvae, spray Bacillus thuringiensis var. kurstaki and cover the leaf undersides thoroughly, since the caterpillars have to eat treated tissue to take in the toxin. Repeat as new hatches appear, and reapply after rain. Bt is a stomach poison - the toxin releases in the caterpillar's gut, it stops feeding and starves. It is very effective on early instar larvae and much weaker on large ones, which is why it is tied to scouting rather than a calendar.

⚠ Bt kurstaki only affects caterpillars that eat treated leaves and is considered pollinator friendly, unlike malathion, which is harmful to pollinators. Spray late in the day to protect beneficial insects and because sunlight breaks Bt down.

Row cover at planting to shut out cabbage maggot and cabbageworm

Lay fine mesh row cover over the bed the day you plant, seal the edges to the soil, and leave it until the flies have finished laying. Cabbage does not need insects to make a head, so the cover can stay on through heading. Both the cabbage maggot fly and the imported cabbageworm butterfly have to land on the plant to lay eggs, and a barrier put on at planting denies them that. Once maggots are in the roots there is nothing to spray - there are no home-garden insecticides for cabbage maggot, which is why exclusion is the whole strategy.

⚠ Do not cover ground that grew cabbage family crops last year. Cabbage maggot flies emerge from the soil, so a cover over infested ground traps them in with the crop instead of out.

Cut when the head is firm, or break roots to hold it

Squeeze the head - harvest when it is full sized, firm and solid, cutting just above the outer leaves. A mature head will stand about two weeks in summer heat and three to four weeks in cool fall weather. If you cannot cut it yet, twist the head a quarter turn or bend the stem over to snap part of the roots. Once the head is solid the plant keeps pushing water into leaves that have no room left, and the head bursts. Breaking some roots throttles water uptake and buys you time without losing the head.