As Shakespeare reminds us, the goodness of manures and composts is often misunderstood

While watching Romeo and Juliet recently, I struck upon an important horticultural truth.

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As a fellow resident of Stratford-upon-Avon, I have long known Shakespeare’s writings to be full of gardening wisdom, and while watching a film of Romeo and Juliet recently, I found yet another example. What words of horticultural truth the old Franciscan, Friar Laurence, utters: “For naught so vile that on the earth doth live/But to the earth some special good doth give.” I thought immediately of my compost bins, simmering in the corner of the garden.

I am not sure that much in my garden can be described as “vile”, although there is certainly precious little that doth not give some good to the earth when it is dug in or applied as a surface mulch.

But the goodness that organic matter offers to the soil is frequently misunderstood, and the biggest misconception arises in the difference between manures and composts on the one hand, and fertilisers (which contain plant nutrients and nothing else) on the other. The really valuable role for manures and composts is as soil improvers, where their combination of sponge-like properties and natural glues enables them to enhance crumb formation both in wet clays and free-draining sands.

But even the best garden compost and the most carefully collected manure contribute relatively little to the soil in terms of plant food. And with a nitrogen-demanding crop such as cabbage, the prospect of attempting it is grim, because even by using one of the most nitrogen-rich organic sources, such as pig manure, you will require an eye-watering 4kg of it per square metre. (Perhaps this is the vileness the old Friar had in mind!) Even then, your cabbages will still be short of potash and phosphate.

It’s easy to lose what little nutrient there is because if fresh farmyard manure is piled in the open over winter, around 10 per cent of the nitrogen vanishes into the atmosphere. Another 10 per cent, together with around 5 per cent of the phosphate and 35 per cent of the potash, is lost to the soil through seepage and being leached out by rainfall.

The message, therefore, is to obtain your manure as fresh as possible, stack it in a compacted form, cover it from the rain and store it on a solid concrete or similar surface.

Much the same advice applies to garden compost, which of course is usually stored in the same container in which it is made. That container should be a slatted bin of around 1.2 cubic metres and manufactured from treated timber. All the proprietary bins I have seen are too small, too fragile or in some other way fall short of my ideal, and I can only surmise that the folk who produce them have never tried making compost themselves. There is an opportunity for some enterprising manufacturer.

All of which brings me neatly back to Act 2 of Romeo and Juliet, where old Friar Laurence is still at it: “I must upfill this osier cage of ours/With baleful weeds and precious-juiced flowers.”

There should be plenty of baleful weeds with which to fill all our osier cages this autumn, but do be wary of two precious-juiced flowers – the roots and rhizomes of those pernicious and invasive species couch grass and bindweed. They are weeds that should only be added to the bin after they have been allowed to fully dry and shrivel. For although I am fairly sure the theoretical maximum composting temperature of 75˚C will kill them, most bins, be they of osiers or any other construction, certainly cannot be guaranteed to achieve this.

This article appears in the 18 September 2020 issue of the New Statesman, Planet Covid

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