We are almost at a big turning point of the growing season, the Summer Solstice, the longest day. We know that day-length influences plant growth, and that after the Solstice, some crops will gradually take longer and longer to reach maturity (others will bolt). Crops more influenced by temperature (like sweet corn) will continue to mature faster while the summer temperatures rise.
Here in central Virginia, most brassicas are planted in spring and again in fall. Unless your broccoli keeps going all summer, consider sowing a new crop for fall. Although it can be hard to think about sowing seeds in mid-summer, it’s very worthwhile to grow fall brassicas because as they mature in the cooler fall days they develop delicious flavor, while weeds and pests slow down. These crops need little care once established. The most challenging part is getting the seedlings growing well while the weather is hot. However, unlike some cool weather vegetables such as spinach and lettuce, brassica seeds actually germinate very well at high temperatures. The ideal is 77-85°F (25-29°C), but up to 95°F (35°C) works. Given enough water, summer seedlings will emerge in only 3 days. Once they have emerged, the challenge begins. As well as temperature and moisture in the right ranges, the seedlings need light (very plentiful in mid-summer!), nutrients, good airflow, and protection from bugs. We deal organically with flea beetles, Harlequin bugs, and sometimes cabbage worms. Our main defenses are farmscaping, and netting (and previously, rowcover).
My book Sustainable Market Farming, has a chapter devoted to Broccoli, Cabbage, Kale and Collards in Fall.
Timing sowing of fall broccoli and cabbage
The number of days to harvest given in seed catalogs is usually that needed in spring – plants grow faster in warmer temperatures. To determine when to sow for fall plantings, start with your average first frost date (as an indicator of cooling temperatures), then subtract the number of days from seeding to transplant (21-28), the number of days from transplanting to harvest for that variety (given in the catalog description), the length of harvest period (we harvest broccoli for 35 days minimum), and another 14 days for the slowing rate of plant growth in fall compared to spring. For us, the average first frost is 10/14-10/20, and we sow 53-day broccoli 21+53+35+14 days before 10/14, which is 6/13-6/19. The last date for sowing broccoli and cabbage is about 3 months before the first fall frost date. In our case that means July 14–20.
Planning and crop rotations for fall brassicas
Our rotation plan shows us a long way ahead how many row feet of fall broccoli and cabbage we can fit in. By the time we order our seeds in the New Year, we know roughly what we expect to grow. In February we draw up a spreadsheet of how much of what to sow when.
Because fall brassicas are transplanted in summer, it’s possible to grow another vegetable crop, or some good cover crops, earlier in the year. An over-wintered cover crop mix of winter rye and crimson clover or hairy vetch could be turned under at flowering, and be followed by a short-term warm weather cover such as buckwheat, soy or cowpeas. Brassicas are heavy nitrogen consumers. To minimize pests and diseases, don’t use brassica cover crops.
Systems for growing fall broccoli and cabbage transplants
The same systems you use for growing transplants in spring can also work well for fall. It can help to have your plants outside on benches, above the 3’ (1m) height of flea beetles. A shade-house might be ideal too. Direct sowing, in “stations” (groups of several seeds sown at the final crop spacing), works for small areas.
We use an outdoor nursery seedbed and bare root transplants, which suits us best. The nursery bed is near our daily work area, so we’ll pass by and water it. Having the seedlings directly in the soil “drought-proofs” them to some extent. They can form deep roots, and do not dry out so fast.
For the seedbeds we use ProtekNet on wire hoops. Choose the mesh size carefully. One with small holes is needed to keep flea beetles away – 25 gm or 47 gm. Overly thick rowcover can make the seedlings more likely to die of fungal diseases in hot weather – good airflow is vital.
Sowing fall broccoli and cabbage
Our rough formula for all transplanted fall brassicas is to sow around a foot (30 cm) of seed row for every 12-15’ (3.6-4.6 m) of transplanted crop row. We aim for 3 seeds per inch (about 1 cm apart). This means sowing 36 seeds for 10 plants transplanted on 18” (46 cm) spacing. And we do that twice (72 seeds for 10 plants!), in two sowings a week apart, to ensure we have enough plants of the right size.Fall Brassica Schedule
Our seedbeds have an 8-week program – see the spreadsheet above for examples of our timing, quantities and varieties. I like to have a regular afternoon every week to grow the transplants. If you’re growing for fewer than 100 people, you won’t need a whole afternoon! Each week after the first week, we also weed the previously sown plants, and thin to 1” (2.5 cm) apart. Then we check the germination, record it, and resow if needed to make up the numbers.
Transplanting fall broccoli and cabbage
We transplant most brassicas at 4 true leaves (3-4 weeks after sowing at this time of year). It is best to transplant crops at a younger age in hot weather than you would in spring, because larger plants can wilt from high transpiration losses. If we find ourselves transplanting older plants, we remove a couple of the older leaves to reduce these losses.
We transplant 6 days a week for an hour and a half or two hours in late afternoon or early evening, for 2-3 weeks. We water the soil in the plot an hour before starting to transplant. It is very important at this time of year to get adequate water to the plants undergoing the stress of being transplanted. Likewise, good transplanting technique is vital. Water a lot more than you do in spring. If you have drip irrigation, you can easily give a little water in the middle of each day too, which will help cool the roots.
We transplant broccoli and cabbage in 34” (86 cm) or 36” (91 cm) rows, which is wider than necessary. Beds or paired rows can fit more plants in the same space, while still allowing room to walk. We hammer in stakes along the row, and attach ropes between them. These both mark the rows for transplanting, and support the netting that we use after transplanting to keep the bugs off. An 84” (2.1 m) width netting can form a square tunnel over two crop rows, giving good airflow. Wire hoops are an alternative. Watering the soil before planting, as well as afterwards, helps survival during the hot summer days.
Aftercare of fall brassicas
About a month after transplanting the broccoli and cabbage (late August-early September), we remove the netting, stakes, ropes and the sticks we use to hold down the netting edges, then hoe and till between the rows. Next we broadcast a mix of mammoth red clover, Ladino white clover and crimson clover. We use overhead sprinkler irrigation to get the clover germinated, and it also helps cool the brassicas. The ideal is to keep the soil surface damp for the few days it takes the clover to germinate. Usually watering every two days is enough. We may replace the netting if pest pressure seems bad.
If all goes well, we keep the clover growing for the whole of the next year, mowing several times to control annual weeds. You could, instead, till in the clover in late spring or early summer to plant a food crop then.
Harvesting fall broccoli and cabbage
We harvest all our brassicas three times each week, and take the produce directly to our cooler.
Our main broccoli harvest period is 9/10-10/15, with smaller amounts being picked either side of those dates We like our broccoli heads to get as large as possible (without opening up) before we harvest. We test by pressing down on the head with our fingertips and spreading our fingers. We harvest as soon as the beads start to “spring” apart. This may be a little late for other growers. We also look at the individual beads and aim to harvest before the beads even think about opening. We cut the stem diagonally to reduce the chance of dew and rain puddling, which can cause rotting of the stem. Later we harvest the side shoots, until they are too small to bother with.
Cabbage heads up from 9/25 and holds in the field till late November. Cabbage is mature when the outer leaf on the head (not the outer plant leaves which are left in the field) is curling back on itself. For storage cabbage, we set the cut heads upside down on the stump, in the “basket” of outer leaves, and come back an hour later to gather them into net bags. This allows the cut stem to dry out and seal over, improving storability.
If you are already looking ahead to the fall, see my post Fall and Winter Vegetable Growing, Harvest and Storage, for lots of links to more info on season extension into cold weather; fall and winter vegetable harvests; and fall and winter vegetable storage. I will write more about other fall brassicas in the near future.