Crop Rotation
Crop rotation is the practice of moving the planting of different crops between one garden bed and another from season to season. There are a couple of good reasons why you might do this, but working out how to do it is a source of confusion for many vegie growers.
Why is it Important?
- To prevent the build-up of soil-borne organisms that lie in wait for particular plants to be grown in the soil, so that they can attack them. This is particularly true of two different vegetable groups: the Solanacaea and the Brassicaea. The Solancaea (or Solanums or Nightshades) are the summer favourites: tomatoes, chillies, capsicums, potatoes etc.) and the Brassicaea (or Brassicas or mustard families) are grown over the cooler months: broccoli, cabbage, cauliflower, Asian greens etc.). To avoid persistent problems, these are the families that shouldn’t be grown in the same bed (or same spot in the vegie patch) year after year, but moved around so that the problematic soil issues don’t occur to spoil the growth of these plants.
- To take advantage of the tendency of some plants to deplete the soil of nutrients during the growing period – and to next plant others that do better in a less nourished soil. This is known as nutrient cycling and understanding how this works means that in the end, you are letting the soil work for you, by understanding a bit about what is happening with each family of plants.
Where to Start?
There are many suggested ways to rotate crops and they can be confusing, as it depends on how many vegie beds you have and the types of plants you have been growing. The following method is one that is easy to follow. It is based on the nutrient needs of the plants and groups them into 4 basic categories:
THE ‘HEAVY FEEDERS’
Solanacae: potatoes, tomatoes, eggplants, capsicum, chilli
Cucurbits: zucchini, pumpkins, cucumbers, squash
Brassicas: Asian greens, broccoli, cabbages, cauliflower, rocket, mustard greens
Others: sweetcorn, spinach, lettuce
THE ‘LIGHT FEEDERS’
Alliums: onions, leeks, garlic, spring onions, shallots.
Root vegies: beetroot, carrots, radishes, Jerusalem artichokes.
THE ‘GREEN MANURES’
Green manures are a seed mix of legumes, to add nitrogen to the soil; and bulky grassy species, such as oats and rye. When these are allowed to grow and then slashed and lightly dug into the soil, they break down to nourish the soil and add valuable organic matter to enrich the soil before the next crop.
THE ‘LEGUMES’
Any of the peas and beans family, including snow peas, peas and broad beans grown over winter; and beans over summer.
Order of Rotation
- After harvesting the HEAVY FEEDERS, next season plant LIGHT FEEDERS in the bed. A top-up with some compost is a good idea but don’t overdo the manures, otherwise the root vegies won’t develop properly, putting on leafy growth at the expense of the root development.
- After a crop of LIGHT FEEDERS, follow it with a GREEN MANURE crop. Leave this to grow until it is about knee-high, or just before it starts to flower and then slash it down and leave it to break down on the surface or lightly till it through the soil.
- After the GREEN MANURE, plant out some LEGUMES. (After harvesting the legumes, resist the temptation to pull out the entire plant. Instead, cut the plants to the ground and allow the roots to break down in the soil as they have stored nitrogen and attract valuable soil micro-flora).
- After the LEGUMES, you can now plant the HEAVY FEEDERS once again. You will need to enrich the soil significantly but the legumes will have also helped the soil and have left a pH that helps with the heavy feeders. If possible, don’t plant the heavy feeders from the same family as was previously planted here, at least for 3-4 years.
It does take some planning to carry all of this out but, by keeping a planting plan diary, you will remember what was planted where over the years. At the very least, try to avoid planting the heavy feeders, especially any in the SOLANACEAE and the BRASSICA families in the same beds in consecutive years.