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Cabbages - Fertilizer Requirements

Cabbage

Soil Test Kit

Soil Test Kit from Harrod Horticultural

Assuming the soil is already quite fertile you are likely to need to supply something like 23g/M2 of additional nitrogen through the growing season for maximum production plus a small amount of potash and phosphate (around 5g/M2)

Lets assume in the autumn you add a barrow load of 20Kg of cow manure to a square metre of the ground.

The manure is around 0.7% nitrogen so you have added 140g of nitrogen. However, nitrogen washes out of the soil and only around 10% of the amount you added is going to be available to the crop.

So we've actually added 14g leaving a nitrogen deficit of around 9g/M2

You've probably got more than enough potash and phosphate in the soil from the manure already but we need to add some nitrogen. Because nitrogen washes out of the soil and these are crops that stay in for a long time, it's best added in a couple of doses through the season. One in Summer and one as the heads begin to form.

We could just use basic fish, blood and bone or Growmore but this would add phosphorus and potash that the soil does not require, although it would be available to the next crop.

Adding a straight fertiliser is, therefore, the most efficient route. You could add 75g/M2 of dried blood (blood meal) split into two doses or 45g/M2 of sulphate of ammonia etc.

In practice you would probably find the manure sufficient although with cabbages a boost as the heads form helps to ensure a good result

If you had not added any manure in the preceding autumn then you could start with a dressing of a general purpose fertiliser, like fish, blood and bone or Growmore the week before planting.

Adding this at a rate around 100g/M2 will cover the phosphate and potash requirement but only adds some 6g or 7g/M2 of the nitrogen requirement. Adding an extra 50g/M2 of dried blood or 35g/M2 of sulphate of ammonia after a month or so will cover the deficit. If you just double the initial amount of general fertiliser, then excess phosphorus and potash will be available for the next crop in the rotation.

For the home grower, without the benefit of soil analysis, feeding is never going to be an exact science. The figures above provide a guide but you will need to adjust if your soil is particularly rich or poor.

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