The importance of crop rotation cannot be overstressed. As a new allotmenteer I was green in more ways than one. I assumed that it was obvious to rotate crops, since all the gardening books start off with it and it seems like common sense. Unfortunately common sense is not as common as it might be. Even now I notice onions, in particular, being grown on the same land, and some grow potatoes year on year which I would have thought was ill advised even for a fairly robust crop. I have noticed that some of the beds on my plot contain clubroot more virulently than others while onion whiterot is found in some and not others. I wonder why that might be?
Division into Beds
I divided my plot up into beds – they are not all equal because I worked round what I was left, and they were different sizes. Some of it was just open land which I divided up into raised beds without an edging, while some had beds that had been edged with retired scaffold boards, which as they rotted had become a perfect breeding ground for slugs. Once I realised this I gradually got rid of them, which is why I am firmly against edging the beds and happily do any necessary restorative work to the edges before planting them up. I have 16 beds altogether discounting the Raspberries, Rhubarb, Welsh Onions which stay where they are, but including Asparagus and Rocket which, as it happens, are on beds 1 and 16, something which I hadn’t realised until I wrote this. The strawberries are also on a ‘permanent bed’ for three to four years, but when the plants are discarded I move new runners onto the next bed down the allotment, thereby hoping to guard against the build up of diseases or pests which might affect the crop, and which, of course is the main reason for crop rotation. There is the added advantage that some crops are better than others at suppressing weeds, some of their roots go deeper which affects the soil structure and some weeds seem to grow best with certain crops. Is it just on my plot that fat hen seems to turn up in the middle of the potatoes when a few days rain follows a dry spell?
French Bean - a Legume
Does the theory work? The books make me laugh because the theory of crop rotation is so very simple. But, like most theories it doesn’t work. It’s based on the scientific observation that legumes like beans - runners, french or broad – and peas convert the nitrogen in the air into nitrates which enrich the soil for growing plants. Therefore you follow these with the brassicas which really like a good feed, also adding manure to the soil, and then finish off a three year cycle with root crops and onions, some of which will grow well without further enrichment, and some, like carrots will positively not want the enrichment or their single root will spread into many, known as ‘fanging’.
Cabbage - a brassica
Do you want equal amounts of each family type?
For crop rotation to work you must want to grow these three ‘types’, of crops in similar quantities, which I for one do not. I keep trying with brassicas and do achieve some success but since I am a perennial underachiever I would be mad to persist in growing them on one third of my site. It would be like banging my head against a brick cabbage. Actually part of the problem is that if the slugs don’t get them the whitefly and butterflies do. Then the soil has to be just the right Ph. It has to have some element or other in it to stop cauliflower going brown. (Incidentally, the French name for a cauli is “choufleur” which sounds so completely different. In fact I call my wife “ma petite choufleur” and she seems to like it.) I’ve had compact sprouts like bullets without compacting the soil and open useless ones with soil like concrete. Then there’s all the pallaver with the collars to stop the cabbage root fly. I’m sure you get my drift. Actually after writing this the only wonder is that I’m still planting even a half bed of assorted brassicas, because you can hardly see me looking optimistically forward to a great crop when I plant them up, can you? I do have some very promising sprouts poking out from inside the mass of whitefly ridden mottled foliage, though.
Early Potatoes- a tuber or root crop
Basic Principles So, it being impossible to follow a crop rotation what can you do? What I have done is to divide my plot up into beds and the plants into groups and followed a set of basic principles, where possible.
1. Brassicas follow legumes
2. Legumes follow a manured crop
3. Never manure carrots or parsnips
4. Don’t repeat any crop with a crop of the same type within four years, more if possible
5. Mark any bed that contains whiterot/ severe clubroot and don’t use at all for onions/brassicas
Parsnip - a rootcrop needing no manure
What needs manure?
Apart from carrots and parsnips everything else gets fed with manure or compost two to three weeks before planting up. The potato/tomato family need manure, while legumes are better with compost since they fix their own nitrogen, and like small amounts of wood ash which provides potash..The manure needs to be well rotted down and the compost like soil. I tend to spread it as a mulch following a wet spell if I am planting up small plants, and lightly fork it in if planting seeds or alium sets near the surface. If the ground has been well manured in the previous year then aliums ( the onion family) do not need more and certainly it does not pay to overdue it unless you want to encourage the growth of the shank for some reason. Most people want a fat bulb. Those with thick necks do not store well. I understand it's environmentally unsound to spread manure in the autumn like my dad did because it wastefully leaches a lot of the nutrients and this means that the water finding its way into rivers becomes polluted. For the same reason I follow the HDRA (Gardening Organic) guidelines of one wheelbarrow full of manure per 10 square metres of ground, which is about one of my larger sized beds, although it’s a bit of guesswork. These days I prefer to obtain fresh horse manure from a supply which I know is pesticide free. There have been scary stories in the last couple of years about contamination leading to severe problems with soil. If I buy the manure in advance or if it is not well rotted I leave it covered, again to stop the nutrients leaching. When I buy it fresh it generates heat much more readily and rots down very quickly. It is important to get to know your soil, not only by checking its acidity/ alkalinity using a Ph meter but in gauging its moisture retention. The soil on our allotment is very well drained, which has advantages, but the downside is it dries out quickly in summer, so organic matter is essential.
Chart which shows the plant types
Leaf Beet Swiss Chard Spinach
Broccoli Cabbage Calabrese CauliflowerRadish
Check PH of soil and lime if needed follows legumes
Do not add manure or compost or fanging is likely especially on carrots
Can be fitted in – does not need a bed alone
Courgette Sweetcorn Cucumber
needs organic matter
Onion Shallots Leek Garlic
Watch where you plant the garlic if you overwinter it for it can help whiterot spread over manuring will cause shanking of necks
French Bean Runner Bean Broad Bean Pea
Prepare a trench for kitchen waste in winter add wood ash and compost