What is crop rotation?
It's the theory of planting particular crops, in a particular order, so that the previous crop leaves behind the nutrients in the soil that the next crop requires to grow. Further, if you keep moving crops then the pests and diseases do not build up in a particular part of your garden.
There are three ways of doing crop rotation (as if it wasn't already complicated enough). I follow the simple crop rotation.
Clear as mud? This might help you understand better...
Crop Rotation - for natural fertilising
This is the most commonly adopted method of crop rotation, probably because it does not require any knowledge of plant families. It instead divides vegetables up into type = ROOTS - FRUITS - LEGUMES - LEAVES. This is because plants of the same type, like roots, need the same nutrients.
You can start anywhere in the rotation cycle.
Legumes have nodules on their roots which excrete nitrogen. So legumes are the best crop to precede leafy plants, as they require nitrogen to grow large and lush.
Leaves are a heavy feeder and will deplete the soil of much of its nitrogen. If you plant leaves, after leaves, your second crop’s growth will be poor.
Root crops are light feeders, and so follow leafy crops which typically deplete the soil of many nutrients, especially nitrogen. Root crops benefit from this because too much nitrogen causes them to grow small roots and beautiful lush leaves, when in fact you are obviously seeking the alternative. Phosphorous is important for good root growth in any plant, but especially when you are wanting them to grow big enough to eat.
Fruiting crops follow roots, and need phosphorous and but also potassium which encourages good flowering and fruiting.
Now the soil has been depleted of nitrogen, phosphorous and potassium, it’s time to plant legumes again to fix nitrogen back into the soil.
Crop Rotation - for pest and disease management
This method requires knowledge of plant families and the particular nutrients, and quantities of those nutrients that each family requires. This method of crop rotation takes a time and patience to master but can reward you with bountiful harvests.
What's the difference between plant "types" and plant "families"? Well, for example, radishes, turnips and swedes are eaten for their "roots" but they are in fact members of the "brassica family". Following this planting method, you would plant these crops along with broccoli, cauliflower and kale, and not with other root vegetables. This is relevant for pests and diseases, because the pests and disease that are prevalent for radishes are the same as othe
r brassicas, and not necessarily other root crops. Following this crop rotation method is beneficial for pest and disease management, because ensuring you do not plant members of the brassica family two seasons in a row helps prevent pests and diseases from building up. But if you give radishes too much nitrogen they will grow leafy and not form good sized roots. This differs from other brassicas like kale where nitrogen is essential because the leaves are the part we consume. So you need to fertilise your plants individually and be more careful about what was planted in the previous season.
I prefer the first crop rotation which focuses on nutrients because I am trying to garden as organically as possible. It is also far simpler!