There is much received wisdom in horticulture that essentially takes a standard idea from agriculture and scales it down to the level of a domestic garden plot. While this might initially seem sensible, it turns out that pretty much every aspect of a garden is totally different to a farmer’s field, so, in reality, this approach rarely works. Perhaps the most important of these mistaken approaches lies in how we fertilise our plots. Changing how you do this will almost certainly save you time, money and even help the environment, too.
A lot of standard horticultural advice is based on the premise that regular applications of fertiliser are absolutely crucial to healthy plant growth. This means lugging around big bags of manure to dig in each autumn, often after a summer of dosing up hundreds of watering cans with liquid feed. According to some advice on growing tomatoes, for example, you’d likely spend more on fertiliser than the value of the fruit you get. However, the scientific reality is that the vast majority of these laborious applications are not just entirely unnecessary, but can actually produce worse results. Excess nitrogen, for example, has been widely demonstrated to result in soft, sappy, growth that is less resistant to environmental stresses, reduces the sugar content of harvests and even suppresses flowering. That’s before we consider the fact that run-off can pollute groundwater and the huge amount of carbon emissions created in the production of fertiliser in the first place.
Why does farming rely so much on fertiliser applications? Well, in agriculture the continual growing and harvesting of crops essentially acts like a pump, depleting minerals from the soil as plants draw them out of the ground and concentrate them in their tissues. These are then taken off site, rather than being returned to the soil. Over centuries, this continual cycle means that most farmland is lower in natural fertility than average domestic plots. Extra applications of nutrients are simply not necessary in most domestic plots for most plants.
The only garden practice that really mimics the agricultural process is conventional lawn care. Lawns do usually need regular applications of fertiliser to keep green and lush, but most trees, shrubs and general garden borders really don’t require external mineral inputs at all – just like forests. (If you have one of those fancy mowers that chops out clippings into tiny particles that are then returned, almost invisibly, straight back into the lawn, you won’t need to fertilise.)
The other exception is plants that are grown in pots, and that’s largely because the compost-based growing media used in them, in particular peat, contain little to no natural fertility and locks users into constantly topping this up with liquid feed applications. In almost all instances, planting everything you can in the ground will free you from the need for 90% of fertiliser applications and, out of porous pots, watering, too. Give yourself more time enjoying your plot than digging manure: ditch fertiliser and you’ll probably see results that are just as good, if not better.
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