Space cabbages correctly

Many factors play a role in the spacing of cabbage – the process is not quite as simple as you might imagine.

The primary objective of spacing is to produce a head size that suits your target market. The rule of thumb is that the closer the spacing, the smaller the cabbages and the longer they take to reach maturity. I once conducted an extensive cabbage spacing trial. It covered 4 000m² and I recorded the weight of every head at the different spacings. A total of 1 711 bags of cabbage were harvested.

Surprisingly, there was no difference in kilogram yield between the closer and wider spaced vegetables. Only the size of the cabbage plants and the time to maturity differed. Of course, some parameters should not be exceeded. You will compromise yield if you plant your cabbages too far apart, as there is a natural limit to the size that a cabbage plant can reach.

If you use a variety that can grow large heads, you will find no significant difference in yield between populations of 35 000 and 65 000 plants/ha.

Upright growers vs ‘spreaders’

Some varieties are more suitable for closer spacing than others due to growth type. A variety with large outer leaves that spread may not be suitable for close spacing. The problem is that, at a young stage, a plant that is a little more advanced than another can start to take over the space of the one alongside and ‘steal’ its sunlight. In doing so, it restricts the other plant’s size potential, leading to unevenly sized cabbages.

Upright growers are better suited to closer spacing. For wider spacing and larger heads, a variety with a spreading growth type is better; it can ‘harvest’ sunlight from a larger area at an early stage, as well as shade out weeds more successfully.Knowing that wider spacing will hasten maturity will help you if you get behind in your planting programme going into winter.Planting times can be critical in winter in cold areas.

Planting even 10 days later can severely compromise yield in some cases. But this can be made up with wider spacing. In my trials, I have not found any great advantage in getting the space between rows equal. On paper it seems to make sense, but in truth the benefits are so marginal that it’s better to space the rows according to convenience.

When planting in beds, the normal practice is to plant three rows, but the plants in the middle row invariably do not reach their full potential as they receive less light. This means that at harvesting, the middle row is often not fully mature. To compensate for this, space plants in the middle row a little further apart than in the side rows.

Getting as close as possible to the edge when planting the outer rows will also help. Even with beds 1,8m apart, consider using two rows and planting closer together in the row to increase the population size. At a 20cm in-row spacing, you will still get a population size of 55 000/ha. This will not compromise uniformity and, at a useful market size of 2,5kg, you can get a yield of 130t/ha, or more.

Spacing affects more than yield and head size, though. Closely spaced cabbages restrict air movement and become a moisture trap. In wet climates in certain seasons, this moisture can cause diseases such as black rot, downy mildew and soft rot.

Stopping the rot

With soft rot, which may not be noticed at harvesting, the leaves at the butt end of the cabbage develop slimy, rotten patches. These continue to spread in bags after cutting and the cabbages may be rejected at the market. Wider spacing can help to prevent this. By advancing maturity, it can also help make the crop less susceptible to disease in general. Black rot, for example, might not be prevented by the wider spacing, but the earlier maturity (which can be advanced by a couple of weeks) can help you to get the crop off before the disease advances to the rejection stage.