Sunday 25 March 2012

Caring for the soil - part 1: crop rotation, companion planting and intercropping

As you know, I have tried do grow organically over these four years or so. I have always believed that working with nature makes more sense than working against it: fire-fighting against pests with chemicals, for example, instead of working in a balanced ecosystem with pests and predators even themselves out - that at least is the thinking.

In my efforts to do and know more, I have been a member of several organisations in the organic sector, among which the Soil Association, but somehow I never bothered why they were called like that. Then, I had a eureka moment earlier this year, when I read something: you should not be fretting so much about your plants but first and foremost care for the soil they grow in, because if the soil is healthy the plants (more or less) then take care of themselves. The soil sustains all life.

So I started thinking: how to take better care of my soil?


I have practised 4-year rotation quite strictly according to Garden Organic suggestions.

Crop rotation is an ancient system, it dates back at the very least to the Romans who apparently called it "food, feed and fallow". It helps with management of both soils and pests, namely:
  • pests and diseases are family-specific, and some of them may persist in the soil, so if you keep growing the same plants over and over again in the same spot you are more likely to be hit; 
  • families of plants use up more or less the same type of nutrients, so if you grow the same plants over and over again in the same spot, they will use up all the same nutrients and there will be little or none left in the soil, leading to all sorts of problems (depletion, erosion etc).
It is exactly the opposite of monoculture, which is the prevailing system in industrial agriculture. 

Rotation works like this. Botanically, plants belong to families. Families with similar characteristics and requirements can be grouped and planted together. Plants from one group should not be planted on the same spot year on year to avoid the problems above. So you divide your plot  in areas (more easily done with beds), and rotate your crop groups. The minimum advised rotation is 4 years, which means you will only plant a group of families in one area once in 4 years. 

Garden Organic suggests to divide plant families in 4 groups (I provide links to Wikipedia but do not bother too much with family names as they change all the time as botanists becomes clearer which plants belong to which family, and whether a family is still a family or some sort of sub or super-grouping of something else).

The groups are labelled A,B,C and D, which I find quite convenient to mark my beds on the plot:

A:  solanaceae (the nightshade family, including tomato peppers and potato), cucurbitaceae (your pumpkins and courgettes);
B:  alliaceae (garlic and onions);  papillonaceae (peas and beans, vetches and clovers);
C:  brassicaceae (the cabbage family, also including spicy salads i.e. rocket and cress); poaceae (the grasses, including cereals and corn); asteraceae (the daisy-shaped flower family, including most salads that are not spicy);
D:  apiaceae (the plant that have flowers umbrella-shaped i.e. parsley, carrots, parsnips), chenopodiaceae (mostly weeds but also spinach and beets) - both families together can be roughly identified as the root crops.

There are other families with less common plants, those are outside the rotation and can make up an extra year in the rotation or could be associated - consistently - with another group.

Crop rotation goes with other methods of soil care, which I am planning to discuss later on.


Of course, even within the sustainable agriculture persuasion (basically anything but monoculture), there are other schools of thought. For example, one that advocates something that is not so neatly organised: "companion planting".  This is also about pairing plants/grouping, on the basis that:
  • some pests locate the crops by sights (mixed planting confusing them); 
  • some plants emit smells that can deter pests from other plants;
  • some plants may provide nutrients for other plants.
There's no excess of scientific evidence of this working - possibly because of lack of interest from science, which nowadays seem to be mostly focussed on technological innovation, genetic engineering to create new and "better" species at the forefront. But it makes sense to me and a notable example of this system was traced back to the Americas where the "three sisters": corn, beans and pumpkins were planted together - corn providing a climbing support for the beans, which fix the nitrogen for hungry pumpkins and pumpkins shading the roots keeping weeds at bay etc.

Yet I have not found a way to make the two systems work together, except in cases where the "extra" plants are out of rotation or within the same rotation group. Not that I have spent too much time exploring this, I barely have time to follow one philosophy, what with gardening around a full time job with travelling, and keeping the house and feeding myself and husband etc. Gardening definitely requires a lot of hands on experience and observation.

Which reminds me it's time to go to the plot, as it's a gorgeous day and there's so much to do.


But I will conclude on a another practice that deserves a mention in this context: intercropping. To make more profitable use of the often scarce resource of space, one could grow quick maturing crops (i.e. salads) while waiting for slower crops to develop. Similarly, catch crops are used in between planting of other crops (i.e. while waiting for the seedlings to be ready in the greenhouse). 

I know next to nothing about this, and I sense there might be a tension between wanting to produce more and the need to keep the soil in good shape - but you may know more.

Please leave your comments if you have experience on any of these practices and how they might work together in a sustainable way.


Carl Legge said...

Hi Paola

In an attemptto encourage you to blog more, I've nominated you for an award here :)

M.Paola Andreoni said...

No pressure at all, then! ;p Jokes apart, that is very nice of you Carl, you are such a lovely person, and friend, and I'm honoured and humbled by your nomination!