What is crop rotation?
Put simply, crop rotation is growing different crops sequentially in the same area. What I'm going to focus on here is a 4-year rotation, as splitting the crops into 4 categories works well. Each category has its own space in the garden, and shifts to another one each year, so by the 5th year everything is back into the plot that it started in.
My posts about the individual categories will go into more detail about growing all of these plants and will hopefully help you decide how to ultimately split up your garden. So from now on in this post when I talk about splitting up your garden, it is only with regards to the 4-year rotation part of the garden. Just bear in mind that if you want any of the other plants mentioned, that you will want space for them too, so the 4-year rotation may not take up your entire growing space.
What are the benefits of crop rotation?
Replace soil nutrients
In order to grow, plants use sunlight, water, and 'food' in the form of nutrients. This means that any plants you are growing will take nutrients out of the soil. Different plants will use different amounts of each nutrient found in the soil, so by growing the same crop in the same location year after year, you will deplete the soil as you'll be taking the same nutrients out every year. This is especially bad for plants that are heavy feeders of one nutrient (like brassicas and nitrogen). So rotating crops can give the soil a 'break' and a chance to add nutrients back into the soil. Some plants, like legumes, will even add nutrients back into the soil. Legumes do this by converting some of the nitrogen gas from the air into a form that plants can use.
Combat disease
If you plant the same crops in the same location year after year, then diseases can take hold, such as club root in brassicas. However, if you rotate the crops, the disease might not have a host plant the following year and may die, and it will be harder for the disease to take hold. There are a variety of diseases that plants can get, but they usually kill the plant or severely damage it, leading to a loss of crop. There are many ways you can attempt to manage diseases, but this is a good place to start to try and prevent it easily and naturally.
Fight Pests
Many insects are host-specific, meaning they will only reproduce (and survive) on a specific plant. If you plant the same plants in the same area every year, it makes it easier for insects to find them and can cause a build-up, with them nesting there year after year after year, making it harder and harder to control the pest population. They use smell, taste or sight to identify plants, so moving the plants each year can reduce the number that are able to successfully find the host plants and manage to lay eggs nearby. This can be combined with companion plants, which I will be releasing a blog about soon, to an even greater effect, and leave you better able to manage the pests.
Splitting up the garden
While there are 4 categories to work with, you can split the garden into 4 or 8 fairly equal sections. The reason for the options of either 4 or 8 is mainly because of potatoes and tomatoes. You don't want to grow potatoes in the same spot every year and the same applies to tomatoes. The same also applies to planting tomatoes after potatoes or potatoes after tomatoes. However, you also shouldn't plant tomatoes and potatoes too close together.
The reason they don't want to be planted in the same place after each other (or themselves) or be planted next to each other is due to the increased chance of disease, which can lead to dying plants and fruit. So this means that if you want to grow both tomatoes and potatoes in a crop-rotation, you either need to plant them far enough away from each other (10ft or 3m) within the same plot, or in different plots to each other.
I would recommend 4 plots if you only want to grow either potatoes or tomatoes, or if you only want to grow one of them in a given year, or if you have space within each plot to have 10ft (3m) between your potatoes and tomatoes, or if you don't mind the risk of having an increased chance of disease impacting them.
I would recommend 8 plots if you want to grow both tomatoes and potatoes and you don't have the space within 1 garden plot to split them up.
If you split the growing area into 8, I'd recommend labelling them A1, A1, B1, B2, C1, C2, D1, D2 or similar, keeping with the 4 categories.
What size to make the plots?
Your plots don't have to be exactly the same shape and size, but getting them roughly the same size in a way that fits the shape of your growing area would be ideal, as then you can grow similar numbers of each crop year after year, not really needing to change your plan much. And if there are some of the plants you don't want to grow as many of in one of the sections, you can fill the space in that section with the other plants that don't need to go into a rotation.
However, if this doesn't suit your growing area or you want to (or don't mind) have, for example, lots of potatoes and tomatoes one year and then not many another year, then you can split the garden into sections of any size. I personally find it easier to have the same sizes so that I don't need to adjust my plans every year, but that doesn't mean it's also the best way for you to do it.
How to do crop rotation?
A 4-year crop rotation is likely to be the best, provided you will be wanting to grow at least some crops from each category.
The four categories are: legumes, brassicas, potatoes, onions & roots.
Legumes, which includes the varieties of beans and peas. Peanuts are included here, but like peppers, they will probably benefit from being grown in a pot or greenhouse.
Brassicas, which includes brussels sprouts, cauliflower, cabbage, broccoli, calabrese, kale, radish, mustard, swede, turnip.
Potatoes, which includes potatoes and tomatoes. Aubergine and peppers are also in this family, but can be grown anywhere in rotation, and might benefit from being grown in pots or a greenhouse anyway.
Onions & Roots: Onion, garlic, leek, beetroot, carrots, celeriac, celery, salsify, parsnips.
Plots in rotation
Brassicas follow legumes because brassicas are heavy nitrogen feeders and legumes can add nitrogen to the soil, providing plenty of nutrients for the brassicas the following year. Onions & roots are last in the rotation because root vegetables don't particularly like soil heavy in nutrients, and it will lead to a lot of leaf growth rather than the root itself (which is the main edible part). Legumes follow onions & roots as the roots break up the soil which is good for legumes.
Plot A - Year 1 is legumes, followed by brassicas in year 2, potatoes in year 3, and onions & roots in year 4. Going back to legumes in year 5.
This order follows in every plot in the garden, just with each plot being 1 year behind plot A. Meaning:
Plot B is brassicas in year 1, potatoes in year 2, onions & roots in year 3, and legumes in year 4.
Plot C is potatoes in year 1, onions & roots in year 2, legumes in year 3, and brassicas in year 4.
Plot D is onions & roots in year 1, legumes in year 2, brassicas in year 3, and potatoes in year 4.
Which plants don't need to be rotated?
There are some common crops that don't need to go into a set rotation like the other crops you are growing. This includes plants in the squash family, corn, salad leaves, and sunflowers. Although it's still recommended to plant these crops in different areas each year, as planting them in the same place year after year can remove vital nutrients from the soil, create diseases and mean pest problems.
Perennial vegetables like rhubarb, asparagus, and 'berries' also don't need to be included in a crop rotation plan. As well as flowers you want to plant around the garden.
What if you don't want to grow crops from every category?
If you don't want to grow crops from some categories, or not enough to fill that plot, then you can plant something else in that plot that year, like the plants that don't need to be in a rotation plan. I would recommend if you aren't filling a plot with legumes, that you add nitrogen to the soil in other ways, such as growing a green manure in autumn and cutting it down in winter and digging it into the soil. You may want to do this anyway, but it's especially important if you aren't growing legumes.
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