With their hefty nature and voracious appetite, cabbages are prone to nutrient deficiencies. When soil is lacking in calcium, the young leaves deform and the edges may look slightly
If you have ever had hollow stems in your cabbages, then you need to add boron to your soil. Many Australian soils are boron deficient, particularly where I live in Tasmania, so I have to keep an eye out for this.
Iron and magnesium deficiency look fairly similar, with both causing a yellowing of the leaves while the veins stay green, but a lack of magnesium affects the older leaves first – while iron deficiency shows up everywhere on the plant. If your soil is low in phosphorus, the older cabbage leaves start to look purple, which can make diagnosis a little challenging if you are growing a purple variety.
With follow-up applications of organic fertiliser every six weeks or so, you should be able to provide the phosphorus cabbages need.
Many creatures will see your cabbage crop as an all-you-can-eat buffet. Grubs and caterpillars are common uninvited dinner guests, but can be stopped by covering crops with fine exclusion netting or spraying leaves with a commercial organic deterrent. Slugs and snails can decimate seedlings and ruin the quality of mature cabbages, so be prepared to maintain appropriate baits, particularly in moist conditions. Aphids seriously reduce plant vigour so you’ll need to hose them off if they are present, or apply a soap spray.
My general advice is to ensure your plants have everything they need – adequate food, water, a good position and soil that drains well – because a healthy plant is better able to look after itself.
I grow most of my cabbages over winter, as many of these pests are less active during that period.
Diseases, such as powdery mildew, downy mildew, rust and leaf spot, may be an issue in wet weather. If you see any foliage that looks diseased, remove it, carefully wrap it up and dispose of it in the rubbish bin to help prevent it spreading.