Rutabaga (Swede)

Sow in summer for a fall crop, about 100 days before your first hard frost

Direct sow a quarter to a half inch deep in rows 18 to 24 inches apart. Count back 90 to 110 days from your first expected hard frost and sow then - in the north that lands in early summer, in the deep south it can be as late as early fall. Seed germinates in 7 to 10 days in warm soil. Rutabaga sizes its root slowly and turns woody and bitter in summer heat, so the crop has to do its bulking in cooling fall weather. A spring sowing runs the root through midsummer and ruins it.

Check boron before you sow - brown heart cannot be fixed later

Get a soil test that includes boron before planting, especially on sandy soil low in organic matter, and correct any shortfall at sowing with borax, boric acid, or Solubor at the rate your soil test calls for. On alkaline soil a foliar application works better than a soil one. Rutabaga is among the most boron-hungry vegetables there is - a long season and a big root mean it draws boron for months, and without enough the root develops soft water-soaked brown centers that hollow out. This is brown heart, and it is invisible until you cut the root open.

⚠ Cole crops are also sensitive to boron toxicity - overapplying scorches the margins of the older leaves. Apply only what a soil test calls for, never a guessed dose. Once deficiency symptoms show it is too late for that crop to recover.

Side-dress nitrogen about 6 weeks after the seedlings emerge

About 6 weeks after emergence, side-dress a quarter cup of 21-0-0 per 10 feet of row, band it a few inches off the row, and water it in. The root does most of its bulking in the back half of the season, and a plant that runs out of nitrogen then stalls with a small root. Feeding at the start instead would only push leaf growth while the root is still tiny.

Thin seedlings to 4 to 6 inches apart once they are up

After the seedlings emerge and have their first true leaves, thin to 4 to 6 inches between plants. Snip the extras at the soil line rather than pulling them, so you do not tear the roots of the keepers. A rutabaga root needs to swell to 4 or 5 inches across. Crowded plants compete for water and room and give you a row of leafy tops over roots that never size up.

Scout weekly for imported cabbageworm and treat small larvae with Bt

Check the tops weekly once the cover comes off. Look for velvety green caterpillars along the leaf midribs, large ragged holes, and greenish-brown droppings on the foliage. If you find them, spray Bacillus thuringiensis var. kurstaki, targeting the early instar larvae and covering the leaves thoroughly, including the undersides. Cabbageworms strip the leaf area the plant needs to fill the root, and Btk is a stomach poison the caterpillar has to eat - it works well on small larvae and poorly on big ones, so catching them early is the whole game.

⚠ Btk kills only caterpillars that eat treated foliage, so it spares the ground beetles and parasitoids that suppress the other brassica pests. Follow the label rate.

Floating row cover at seeding to shut out cabbage maggot and flea beetles

Lay floating row cover over the bed the day you seed and bury or weight the edges so no fly can walk under. Leave it on through seedling establishment. Do not put the bed where brassicas or root crops grew last year - rotate to fresh ground, since the maggots overwinter as pupae in the soil where last year's crop stood. Cabbage maggots tunnel through the root itself, which is the part you are growing, and no amount of later spraying reaches a maggot inside a root. Flea beetles shothole the cotyledons and can outright kill a just-emerged stand. Both are barrier problems, and the barrier only works if it goes on before the pest arrives.

⚠ What chemical control exists for cabbage maggot is preventative only - soil and tray drenches applied before the fact. Once maggots are already feeding in the root there is no insecticide that will reach them, so exclusion and rotation have to carry the crop and a rescue spray is not a fallback. Adult flies are drawn to decaying organic matter, so terminate cover crops or green manure at least 3-4 weeks before planting where you can.

Store cold and damp, or heavily mulch and dig through winter

Store the roots at 32 to 35 F and 90 to 95 percent relative humidity, where they hold for two to four months and often longer in a root cellar. Alternatively leave them in the ground under a heavy mulch and dig as needed until the ground freezes hard. Rutabaga wants cold and damp. A refrigerator is cold but dry, and the low humidity makes the roots shrivel and sprout instead of keeping.

Dig at 4 to 5 inches across, after the plants have taken several frosts

Lift roots once they are 4 to 5 inches in diameter and the plants have been through several light frosts. Trim the tops off about an inch above the crown and remove the long thin taproot. Handle the roots gently and knock the loose dirt off without cutting or bruising the skin, which is what lets them keep. Frost is what makes a rutabaga worth eating - chilled plants convert starch to sugar, so a root pulled before frost tastes flat and sharp while the same root pulled after tastes sweet. 4 to 5 inches is the size extension guides target; some varieties are bred to go larger without coarsening, so go by the size your variety is sold at rather than pulling everything at 5 inches.