Closed Loop or Self Fertilising Vegetable Gardening

I aim to grow vegetables in a way that uses little or no outside inputs. This means no manure, no fertiliser, no pesticides, no nothing. Of course this is going to be very difficult but over the last couple of years I have made headway. My back garden is now a rich dark loam with mid to high nitrogen. Vegetable gardening requires large amounts of fertility to create satisfyingly large vegetables. By taking them away and eating them we rob the soil of that fertility, which is why traditional veg growing (even organic growing) requires us to both manure and to use fertiliser to grow the sort of good quality vegetables we are used to buying in the supermarket or greengrocer.

What is wrong with importing manures and buying fertilisers?
Manure is made by animals which themselves require land and to be fed grain. The grain that feeds the animal that makes your manure also requires land to be grown, which in turn needs manure and fertilisers. And so on and so forth. Organic fertilisers and manures require large resources (land) to make, and synthetic fertilisers need large amounts of energy and fossil fuels to manufacture. In the future, when the fossil fuels run out (which they will) fertilisers and manures will become expensive or even unavailable (as in ww2, another resource limiting crisis) so using closed loop fertility techniques on our own plots will help us become self sufficient. Of course scientists may make the next great leap forward, find new ways to manufacture fertilisers without the use of fossil fuels and these techniques may become unnecessary, but let’s not rely on that entirely, eh?

If I am not going to import manure and fertiliser how exactly do I aim to grow said vegetables?
Well, I will use (and have been using) the following techniques: growing green manures, composting plant residues, composting household wastes, making nutrient rich teas and setting land aside (ie, not using it directly for growing food) to grow composting and mulching material. So, for example, I overwinter all empty parts of my plot with a green manure (usually a nitrogen fixer like winter tares). In the spring I will either dig the green manure in and sow a food crop two weeks later, mow the green manure, dropping it to the ground and forming a mulch then sowing a food crop into the mulch, or allow the green manure to mature over the summer and thus fixing quite useful amounts of nitrogen into the soil for a food crop next year. I will also compost all waste from the house including bills and newspapers. Because society does not yet accept the composting of human faeces (a method that let China’s agriculture remain sustainable for 4000 years), I am not going to do it. I do however pee into a watering can and from there feed my comfrey plants and compost heap. Though non gardeners may find this revolting it is a long standing practice and socially acceptable (at least in Britain). Nutrient rich teas can be made from my comfrey and compost (amongst other things) to give my plants a boost when they are flagging. But here’s the tricky bit – setting land aside to grow compost and mulch.

Just how much land do we need to set aside to maintain the fertility of the plot?
The answer may be “nobody knows”, or maybe “it all depends on the nature of your plot”. But here are some answers from other people doing similar closed loop gardening systems. Biointensive gardening sets aside 60% of the plot to crops that are bulky enough to make good compost that will be adequate to feed next year’s crop. Those compost crops also have edible parts, so broad beans are eaten and the nice, bulky nitrogen and carbon rich stalks are composted. With Stockfree Vegan Organic farming 2 out of 7 years the land is left to lie fallow with a nitrogen fixing green manure. So 28.5%, but none of the fertility support plants are cropped for food. It should be added that some compost or chipped wood is added because yields can drop off after a number of years but I couldn’t ascertain, from my reading, how much chipped wood or compost. Permaculture: permaculture is more a design methodology than a technique like the other two systems but from studying some quite famous permaculturist’s designs about a third is about right with from 50%-100% of the support plants being often permanent nitrogen fixing trees which are cut back to provide lots of nitrogen rich mulch for the food crops. Very often designs (with permaculture) change over time. So while establishing a food forest a permaculturist may cover his entire plot with annual nitrogen fixing green manures for the first year and then introduce the productive plants as the soil becomes more productive.

In my case I am using about half of the plot given over to fertility support plants. About a third of those are comfrey plants which aren’t nitrogen fixers (but do provide nitrogen). Because they don’t fix their own nitrogen they need fertilising which is where the urine comes in. If you are squeamish about this then use some of your very limited (and therefore very precious) compost to feed the comfrey. Cut the comfrey several times a year and make it into tea to feed your food crops. This may sound daft – feeding a plant to feed other plants, why not just feed the food crop with the compost? – but the comfrey is very efficient at scrounging every morsel of nutrient from deep undergound, from eroded rocks, dying microbes and the juices from your compost and urine. It’s like a catalyst for your garden and you will see this when your plants perk up from comfrey tea.

Putting a half of our very precious space to non cropping plants may seem excessive but for me it is insurance against a bad crop. I am also ensuring that my soil is building up with organic matter, an investment in my garden’s future. In my backyard some of this space is hedges, so it has a dual purpose of protecting my privacy and building a microclimate that protects my food plants. Some of the support plants are also very pretty: sweet peas (both perennial and annual), lupines, crown vetches and crimson clover. So they provide fertility, provide habitats to beneficial insects, benefit the soil and please my eye. Wherever there is empty space among my cropping plants I bung in a few broad beans or winter tares to cut later for compost or mulch.

A few words on intercropping and staggered sowing of green manures. Green manures can be sown underneath and amongst food crops but they will – at least early in the life of the food crop – compete with the food crop for water and nutrients. If the green manure has already been through the winter then it can be cut back (to about half height) and this will release both nitrogen to the surrounding soil (and thus your food plants) as well as give your food plants the advantage when it comes to competing for resources. The green manure then regrows. Otherwise you can sow green manures after the food plants are established. If you know your food plants will crop into the autumn and you are worried your next overwintering green manure won’t be established before winter you can undersow your food crops in late summer, early autumn which will gather useful amounts of nitrogen in the often fine weather of autumn whilst not really affecting the food crops which by now have developed extensive root resources.

How do I know all of this is working?
The proof of the pudding is, as they say, in the eating. Nice big crops of tasty vegetables should do it. But a harvest today is no guarantee of one tomorrow: is the soil improved? is there plenty of organic matter in the soil? is it dark? Is your pile of compost and/or mulch adequate to feed and protect the soil for next year?

And let us not forget science. We (certainly I) need to record our food crop yields over several years and publish them so that others can gauge whether or not we are talking rubbish. And we need to be honest. Some permaculture/organic theory has the whiff of snake oil about it so we need to prove the naysayers wrong with facts and figures.

Our soil may be bulging with goodness but we can also confirm this by a soil test. I bought a cheap kit (£18) from a garden centre that measured pH, nitrogen, phosphates and potassium, but you can also get proper professional testing where you send off samples in the post. For me, 4 or 5 tests around the plot with my own home kit gives me a good indication of what is going on in the soil. I have at the moment medium and sometimes high nitrogen in my soil, a result that cheered me up no end. Nitrogen is not the only nutrient and it is for this reason we must be militant in our making of compost and mulch. We can never make enough!

This is my guide so far of how to make your garden self fertilising in a closed loop manner. It is the basic principles which I use, the record of which I will keep as a permanent article on the website. As I think of more things to add I will add them and post to the main page that I have updated this article.

Cheers all…

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