Tips and tricks to keep your brassicas flourishing

by Jackie French July 13, 2022

This is confession time. I have been torturing our cabbages. And our cauliflowers, Brussels sprouts and broccoli plants. For the last five years I’ve been giving excuses for the cauliflower’s increasingly thin and twisted leaves: it’s a drought, it’s too hot, there’s a bushfire, it’s too wet.

It is time to face the truth. Even though our cabbage-family plants the brassicas, which includes caulis and broccoli, are well fed, their tucker has mostly been compost, made from the weeds or prunings or gone-to-seed veggies in our garden, with local hay to mulch them. Sadly those local plants are deficient in exactly the nutrients our caulis now lack: molybdenum.

Molybdenum is a trace element that all plants need. Most cheap plant foods don’t contain trace elements. If you make compost from plants grown in soil that is deficient in trace elements, your compost will be trace-element-deficient too.

If your cabbages or caulis have thin or twisted leaves, brittle or pale areas between the veins, and general poor growth and lack of hearting, you can be pretty sure they need molybdenum. Pale areas between the veins of the leaves in many other plants is a sign of molybdenum deficiency too.

Thirty grams of molybdenum dissolved in hot water used as a foliar spray for every 10 square metres of leaf is effective. Leaves from old healthy cauliflowers or cabbages from the supermarket are a good source of a molybdenum-rich material to use for compost, or buy a trace element mix from your garden centre.

Deficient in calcium

Brassicas don’t mature well in very acid soil or where the soil is deficient in calcium. They may also turn slightly purple if they lack phosphorus and won’t thrive with a lack of magnesium.

The easiest short-term fix is to add lime, dolomite or wood ash to make the soil more alkaline, as plants don’t take up molybdenum and other trace elements well in acid soil.

Most years you can just bung plants in, feed, water and pick. Every decade or so buy a small container of trace elements, either for the soil or to spray on the leaves. Your garden will have enough trace elements for a decade or so. That’s what I did 20 years ago, and we are only seeing deficiency now. I must also remember to add just a small scatter of alkaline wood ash to our cabbage patch — something I haven’t done for about three years either.

Wood ash makes soil more alkaline and helps relieve potash deficiency — just don’t add too much. A gentle sprinkle, like icing sugar on a sponge cake, is plenty. Dolomite is better than lime as it can correct any tendency to magnesium deficiency.

Feed well

Feed your brassicas well. A mulch of horse manure is superb; otherwise, give a light dressing of nitrogen-rich fertiliser like chicken manure and blood and bone every two weeks until the cabbages begin to form heads, the caulis produce cauliflower and the broccoli makes baby broccoli.

Spray caterpillars

To get rid of caterpillars, make a glue spray: mix one cup of boiling water and one cup of white flour, then add enough cold water to make it sprayable. Sieve it well before putting it in your sprayer or it will clog up, and soak your sprayer after use. Glued-up caterpillars stop eating. Flour is also toxic to caterpillars, but not to the birds who will eat the suddenly motionless pests on the leaves. The flour will look messy, but nothing a good hosing the next day can’t restore.

Every gardener knows that home-ripened tomatoes have a flavour and texture unlike any bought in a supermarket or that have been cold-stored. But you need to have tasted a cauliflower or cabbage straight from a chilly back garden to know how truly sweet they are when just picked and not stored for even a few days in the fridge.

All supermarket broccoli I’ve tasted had a faint undertone of sulphur. Home-grown broccoli, especially after it’s been winter chilled, is magnificent.

Forget rubbery summer coleslaw, and try winter crisp coleslaw instead, dressed with a sprinkle of caramelised balsamic vinegar and extra-virgin olive oil with just a smidgen of salt. Winter coleslaw is especially magnificent when made with red cabbage.

Other brassica varieties

There are some glorious brassica varieties around these days, like Italian calabrese broccoli. It’s possibly the most tender of all broccolis, with pale green heads and plentiful side shoots after the main head has been picked.

There are the quick-maturing Asian members of the cabbage family, too, like buk choy and wombok, perfect for stir-frying or steaming with a touch of oyster sauce. But for now, my heart belongs to red cabbages.

They are the king of cabbages, big and hard and round and brilliant keepers. You can slice off the top and stuff them with a rice or mince-based stuffing and slowly simmer them in stock for five hours or till tender.

It’s important to pick cabbages while they are still firm. They’ll stay firm for months in cold or cool weather but may quickly go to seed in hot weather. The best way to check your cabbage is to squeeze it. If it feels spongy it’s going to seed. Some varieties hold better than others. In wet or humid weather, pick your red cabbage as soon as it feels firm.