Grow your own manure
A green crop (aka ‘cover crop’) improves moisture retention and drainage. As well as providing bulk nitrogen, it will draw deep soil minerals up to the root zone. Green crops block weed growth, protect the soil in heavy rain and make the garden easier to dig in spring. As the roots grow during the winter months they keep the soil aerated and reduce compaction. Green crops also help break disease cycles.
In New Zealand gardens the traditional green crops are lupins and mustard. Wheat, barley or oats may also be used to add organic bulk. Or a mixture may be sown. Mustard helps against problematic soil fungi but should not be sown in soil that has just had a brassica crop. Lupins add extra nitrogen via special ‘nitrogen fixing’ bacteria in their root nodules which take nitrogen from the air and convert it into a form that plants can use.
Lupin is best dug in just before flowering. If you want to enjoy the blue flowers you can dig it in just after flowering, but flowers do take some of the nitrogen from the soil. You will also need to factor in time for the green matter to break down before you plant your spring crops. Allow at least three weeks, ideally six. When digging in your green crop, take the opportunity to dig in lime and animal manure at the same time.