A young man parked a heavily laden pickup in the village one afternoon recently and a few minutes later appeared at our front door and asked if I was interested in gardening. He was, as I find myself telling people of his tender years, “too young to know who I am”, but in the event I played dumb and when he enquired if I would like to buy some bags of chipped bark for my garden I thanked him but said I already had plenty of organic matter.
Nonetheless the episode served as a useful reminder because I am sometimes asked about the garden value of bark and other tree waste – wood shavings or even sawdust. The short answer is that all organic matter can find some useful purpose in the garden and tree waste from deliberately cropped softwoods is a renewable resource. But what attributes does it have? Certainly not much in the way of the three most important plant nutrients. The nitrogen content is only about 0.2 per cent, while the phosphate and potash are scarcely measurable. But it is certainly valuable as simple organic bulk, helping with other organic materials to improve soil structure and maintain its moisture content.
However, tree waste will only achieve this properly after it has been composted, because if it is added directly to garden soil when fresh, it will temporarily deplete the nitrogen content as it begins to decompose.
And depending on the trees from which it is derived, it may also supply chemicals toxic to plants that a year or more in a compost bin will allow to degrade or leach away.
The best use of composted tree waste is as a mulch when it can be used in the same way as garden compost, rotted manure or leaf mould.
I love the word mulch. As a noun, verb or even, in its oldest Middle English form, an adjective, it seems to embody everything worthy about gardening organically; of communing with Mother Earth. And I always think of March as the mulching month par excellence.
The main benefits of mulching now are twofold: first, by forming a blanket over the soil surface, the mulch will cut down water-loss by evaporation; or, to put it another way, it will maintain the soil moisture in pretty much the same state as when it was applied. This is important and often overlooked: a mulch will keep a dry soil dry, just as readily as it will keep a wet one wet.
The second use of mulching is at least as important because if you lay an organic blanket over the soil surface, weeds are starved of light and although no deep-rooted perennials will be inhibited, annual weeds can be totally suppressed. The time and effort saved in hoeing and hand-weeding is remarkable; because I put an 8cm-thick mulch over all my borders now, I doubt if I have to use the weeding hoe among them more than once or twice during the summer.
March is an appropriate month for both reasons because the soil is still moist from the winter rains and annual weed growth is only just getting into its stride.
We do nonetheless have one rather different use for fresh – not composted – tree bark: making it the raw material for low-cost rustic paths around the garden, confining it by lengths of half-round farm fence rails, held in place with wooden pegs. I bet the young man with the pickup had not thought of that.
This article appears in the 06 Mar 2019 issue of the New Statesman, The next crash