Crop rotation – The theory
Crop rotation can seem a bit daunting particularly when you read conflicting advice in gardening books and magazines. Crop rotation essentially entails not growing the same plants in the same area year after year in order to prevent the build-up of disease and pests and the depletion of soil nutrients.
To help plan crop rotation, plants are grouped into families and/or plants requiring the same growing conditions and treatments. Below is a general crop rotation found in most British books based on UK preferred crops:
Crop rotation over a 4 year period on the same piece of ground
So if you grow potatoes in one area in one year, you would then follow the same area with legumes in Year 2 then brassicas in Year 3 and roots in Year 4. Whichever point you start at, you always follow the same direction of travel. If you do not grow potatoes, then you could replace this with members of the squash family for instance as they also like a rich recently manured fertile soil.
There is a great deal of conflicting advice regarding legumes. Legumes are able to fix their own nitrogen and one of the theories is that if you follow a legume crop with brassicas, the nitrogen is then available for the brassicas to take up. I have also read that this is not true and that you would have to dig the spent legume crop into the soil for the next crop to benefit from nitrogen release. Below are the main and most common vegetable families (in blue, relatively easy vegetables to grow to get you started). When designing a rotation, members of each family can be grouped in one area and with members of other families if they share the same growing requirements.
. Potato family – Solanaceae
Potatoes, tomatoes, aubergines, peppers.
Potatoes prefer an acid soil so don’t grow where you have just added lime. All these plants are greedy feeders. I would not plant potatoes and tomatoes too close together though as they are both highly susceptible to blight and best kept apart. Your tomatoes could be grown with your legumes.
. Legume family (Leguminosae)
Broad beans, french and runner beans, peas,mange tout.
These fix their own nitrogen but do like a moisture retentive soil and may need regular watering if the weather is very dry. You could prepare a trench and dig in kitchen waste, leaves, etc… prior to planting to improve water retention. Incorporate plenty of compost/manure if your soil is on the sandy side.
. Brassica family – Brassicaceae (Cruciferae)
Broccoli, Brussels sprouts, cabbages, cauliflowers, kale, kohl rabi, mustard, radishes, swedes, turnips, mizuna, rocket.
Firm the ground well when planting large brassicas to prevent the stems rocking in the wind. Obviously, the larger the brassica, the greedier it is in terms of nutrient requirements. These plants are nitrogen-demanding, however the smaller crops such as radishes, turnips, mizuna and rocket can pretty much be fitted anywhere on your plot. It is not unusual for me to grow these less-demanding brassicas in the same bed as my carrots and parsnips
. Carrot family – Apiaceae (Umbelliferae) referred to as ‘Roots’ in the diagram.
Carrots and parsnips.
Do not plant these on recently manured soil otherwise the roots will fork. These crops need a light stone free soil so clay soils may need to be opened up by adding leaf mould.
Celeriac and celery also belong to this family but confusingly have different growing conditions and are far more demanding in terms of nutrients so these latter two are best combined with the potato family or in an area to which manure or compost has been recently added.
. Beetroot family – Chenopodiacea
Beetroot, spinach, swiss chard, good king henry.
These plants are not too fussy but will need moisture retentive soil as they can be prone to bolting if weather conditions are dry and hot. They can pretty much fit anywhere in your rotation if their requirements are satisfied, such as growing them amongst the legume bed. They can also withstand some shade.
. Daisy family – Asteracea (Compositae)
Chicory, lettuces, salsify.
These are fairly undemanding but lettuces will need watering as they can bolt easily. They can pretty much fit anywhere in your rotation.
. Marrow family – Cucurbitacea
Cucumbers, courgettes, melons, pumpkins, squashes.
Rich fertile manured water retentive soil is required. These could be grown with your potatoes or with the legumes if you have manured the legume bed.
. Onion family – Alliaceae
Onions, garlic, leeks, shallots.
Well drained but rich fertile soil is required. Winter leeks can follow a potato crop in the autumn. I would not recommend planting members of the onion family year after year in the same spot as white onion rot can be problematic. So, if you have grown leeks in one area one year, don’t follow them the year after with onions or garlic but choose an entirely different vegetable family. You could plant this family in the same area as your legumes.
Now things can get a little complicated if you grow more potatoes then say brassicas or if you follow your summer crops with winter crops and unless you’re adept at the hard level of Sudoku, things can… well… get in a little bit of a pickle.
Crop rotation – The practice
So the answer to the rotation question is YES, do rotate if you can, but real life and your food preferences sometimes mean that in practice following a strict 4-year rotation as illustrated above is simply not practical.
There are however some key principles to remember:
– Keep a record each year of what you’ve grown where and try not to grow the same thing in the same area year after year, leaving a minimum gap of 3 years if at all possible. If you can’t, I would definitely avoid growing potatoes and brassicas in the same area each year and would aim to leave at least a 3-year gap for these two families of vegetables but would not get too hung up about the roots and legume families.
– Look at how your crops have performed every year. If you find yourself having to water your peas and beans every day, then it’s time to improve your soil water retention capabilities by adding leafmould, manure and any bulky organic matter. If your potato crop has been disappointing, then next time around, ensure you add manure and compost to the area (but do not overdose – see February blog). If your onions are hit by white onion rot, then it is time to avoid planting them in the same area next year.
– Get to know your crops and their requirements.
I think of my crops as either greedy crops that will definitely not perform in poor soil (such as potatoes, large brassicas such as cauliflowers and Brussels sprouts, pumpkins and squashes) or undemanding crops (such as legumes, beetroot, carrot, turnip, salad leaves, etc.).
So if you can’t follow a 4 year rotation plan in the order shown above, alternate greedy feeders and undemanding crops. So for example, in year 2, I certainly would not grow pumpkins and squashes straight after my potatoes but if I did not fancy growing legumes (as part of the classical rotation plan), I would plant the area with some less demanding crops such as carrots and parsnips to follow on from potatoes.
Baffled and confused? Ready to give up? Don’t despair. As long as you remember the key principles above, get to know your plot and your various crops and experiment, you will be rewarded with a wonderful and tasty array of crops.