Across much of the country, the first frosts have arrived or are on the way. For tomatoes and peppers that's the end of the road. For the cabbage family, it's when the good part starts. Brussels sprouts, broccoli, cabbage and kale all handle cold well, and a few light frosts make them noticeably sweeter. If you've got brassicas in the ground right now, here's how to get the most out of them before winter really sets in.
Why frost makes brassicas taste better
When temperatures drop, cold-hardy plants turn some of their stored starch into sugar. The extra sugar acts like a natural antifreeze in the plant's cells, and it also takes the edge off the sharp, sulfury bite these vegetables can have in warm weather. That's why a Brussels sprout picked in late November tastes so different from one picked in September. You don't need a hard freeze. A couple of nights around 28–32°F is enough to make a difference.
Brussels sprouts: pick from the bottom up
Brussels sprouts are the slowest of the bunch, and fall is when they finally pay off. Sprouts mature from the bottom of the stalk upward, so start low:
- Harvest when sprouts are firm and about 1 to 1½ inches across. Snap or twist them off, and remove the yellowing leaves below them as you go.
- "Top" the plants for a bigger final harvest. If your sprouts are still small and you want them to size up together, pinch or cut off the growing tip at the top of the stalk. The plant stops putting energy into height and sends it to the sprouts instead. Do this about three to four weeks before you want your main harvest.
- Mature plants are tough. Established Brussels sprouts usually shrug off temperatures down into the low 20s°F, and often a bit lower. When a hard freeze in the teens is forecast, harvest what's left, or pull up the whole stalk. Sprouts keep well on the stalk in a cold garage or the fridge for a couple of weeks.
If you didn't grow them this year, put Long Island Brussels Sprouts on next year's list. It's a classic, compact heirloom that does well in home gardens. Just plan ahead: it needs a long season, so for a fall harvest, start seeds in late spring or early summer.
Broccoli: cut the main head, then keep picking side shoots
Broccoli needs to come in at the right moment. Harvest the main head while the buds are still tight and dark green. Once you see yellow, the flowers are opening, and quality drops fast. Cut the stem at a slant about 5 to 6 inches below the head. The slant helps water run off the cut stem.
Don't pull the plant yet. Most heirloom broccoli keeps pushing out smaller side shoots for weeks after the main harvest. Calabrese Broccoli is especially good at this. Keep cutting the side shoots every few days and the plant will keep making more until the weather turns truly cold.
Mature broccoli handles light frosts, around 28°F, without much trouble. A hard freeze in the mid-20s or below can damage developing heads, so pick anything usable before a cold snap.
Cabbage: firm heads, and how to keep them from splitting
A cabbage is ready when the head feels solid when you squeeze it. Cut it off at the base with a sharp knife. If you leave the stump in the ground and cut a shallow X across the top, many plants will grow a few small bonus heads.
The main fall problem is splitting. Heavy rain after a dry spell makes the head take up water faster than it can expand, and it cracks open. If heads are ready but you're not, give the whole plant a firm quarter-turn twist, or slice down beside it with a spade. Breaking some of the roots slows water uptake and buys you a week or two.
Mature cabbage handles hard frosts well. Red types like Red Acre are known for holding and storing especially well. Whole, unwashed heads with a few wrapper leaves left on will keep for weeks, and often months, in the fridge or in a root cellar kept just above freezing with high humidity.
Kale: the last one standing
Kale is the hardiest of the group. Many varieties keep producing through nights in the teens, and under a row cover or in a mild winter you can pick it all season. Harvest the lower, outer leaves and leave the center crown alone so it can keep growing. Leaves picked after a frost are noticeably sweeter and more tender, which makes this the best time of year for kale salads. Red Russian Kale, with its flat, purple-veined leaves, is one of the mildest and most tender options.
A quick cold-tolerance cheat sheet
These are rough guides for established plants. Wind, moisture and how gradually the cold arrives all matter, so treat these as starting points:
- Broccoli: fine with light frost (about 28°F); protect or harvest before the mid-20s.
- Cabbage: handles hard frosts into the low 20s; heads can be damaged by repeated freezes in the teens.
- Brussels sprouts: comfortable into the low 20s, often lower.
- Kale: the toughest; many varieties survive the teens, more with a row cover.
A lightweight frost cloth or old bedsheet thrown over the plants on the coldest nights can easily add a couple of weeks to your harvest. Take it off when the day warms up.
Already thinking about next year?
If this season reminded you how good homegrown brassicas are, here's the timing to remember. For a spring crop, start broccoli, cabbage and kale indoors about 6 to 8 weeks before your last frost and set them out a few weeks before that date. They like cool weather and can handle a light frost. For a fall crop like the one you're harvesting now, start seeds in mid-summer, and start Brussels sprouts earliest since they need the most time. Write down what worked this year while it's still fresh. Your future self will thank you.
Happy harvesting!