How to keep soil healthy, happy and productive

In much the same way that most great meals are made using a combination of skill, knowledge, passion, artistry and the right tools as well as, most importantly of all, the best of ingredients, so it is with most great gardens. So it doesn’t matter, for example, how brilliant a chef Alain Ducasse is or how many Michelin stars he has garnered so far over the course of his glittering career (21 at the last count), he’s still never going to be able to rustle up his signature bouillabaisse, sauté gourmand of lobster or truffled chicken quenelles without those essential staples. Likewise, no matter how great a gardener you are, you’re never going to be able conjure up your very own leafy oasis without that most important of horticultural ingredients, which is a half-decent soil.

I say half-decent because perfect soil is something of a horticultural unicorn, an elusive thing that gardeners can spend a lifetime pursuing. A deep, dark, friable loam, rich in organic matter, its structure perfectly intact, its soil life thriving and in balance, free-draining yet moisture-retentive, with a ratio of sand to silt to clay of 40:40:20 and an optimal pH of 6.5 is the gold standard. But in real life, endless permutations of this can be found in our allotments and gardens, from loamy sands, silty loams, and sandy clays to silty clay loams and sandy silt loams.

Of course, most of us, most of the time, don’t use these kinds of technical terms to describe the soils we garden on. Instead, gardeners use what you might call good horse sense when it comes to identifying the bad from the good. We can usually tell, for example, just by the look, the feel and sometimes even the smell of it, if a soil is inclined to be heavy, sticky, cold, or slow to drain in winter (all signs of a high clay content). We soon learn that if it’s thin, pale, light and stony, then these are signs that it’s low in organic matter. Likewise, we also know that if it’s a “half-decent” soil, it will be dark brown in colour, crumbly in texture and relatively easy to dig.

The way it looks, feels and smells aside, there are other simple ways to gauge the quality of your soil. Plenty of earthworm activity, for example, is a very positive sign, signalling fertility, good drainage and thriving soil health. In really healthy soils, you can often find up to 250 of these “ecosystem engineers” (or “nature’s ploughs”, as Charles Darwin referred to them) per cubic metre, with each earthworm daily consuming its own weight in dead plant matter) and annually helping to produce several centimetres of premium quality top soil. Earthworms also help to manage soil-based pests and diseases and encourage the presence of beneficial soil-based fungi and bacteria while their constant burrowing brings valuable plant nutrients closer to the surface where they are more easily reached by hungry root systems.

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Another clear sign of good soil is the abundant growth of certain common weeds such as nettles, groundsel and fat hen, all of which indicate fertility. This is why you’ll often spot these weeds growing near the site of old manure or compost heaps, or close to old cow barns or stables. Conversely, the presence of other weeds can often be a sign of nutrient deficiencies (for example, ragwort), or of a poorly drained soil (for example, bittercress or dock) or a compacted one (scutch, bindweed).

Unfortunately, even the best of soils can still sometimes suffer from damage that’s beyond our control. Anyone on good terms with the soil in their garden or allotment, for example, will know that the extremely heavy rainfall experienced in most parts of the country in recent months has been bad for soil health, especially bare soil exposed to the elements, making it vulnerable to “capping”, compaction and surface run-off.

In the case of capping, very heavy rain causes the surface layer of the exposed soil to form an impermeable, almost greasy crust that blocks the soil’s tiny pores and reduces its ability to breathe and to drain freely, with negative consequences for all the micro-organisms that inhabit it. Soil capping also makes it very difficult for most seedlings to germinate.

Even more serious than soil capping, soil compaction is caused by repeatedly digging, working, walking on or driving across wet soils, all of which compresses the soil particles and important air spaces or pores between them. This in turn damages soil health, its structure and its ability to drain easily, reduces the ability of soil organisms to function properly and makes it difficult for plants to grow well by interfering with their ability to develop vigorous root systems, access nutrients and survive weather extremes. As for run-off (a form of soil erosion), this happens as a combination of heavy rainfall and soil compaction, with soil particles being washed off the surface of the waterlogged soil on to paths, roads and paving.

What to do? We can do a lot to help protect and fortify our soils with the regular use of organic mulches, home-made garden compost, living “green manures” and other soil conditioners and improvers such as biochar, powdered seaweed, and probiotics and prebiotics such as Free N100 and Soil Renew (suppliers include mrmiddleton.com and fruithallfarm.com). Avoiding the use of impermeable paving and making space for trees, shrubs and hedges in our gardens and allotments also helps to protect soils from becoming waterlogged.

[ Your gardening questions answered: How can I improve the soil in my flower beds? ]

We can also minimise the risk of damage by always giving soil sufficient time to recover from heavy rainfall, before carrying out routine tasks such as digging or weeding beds, cutting the lawn or planting. If you do have to walk or work on wet soil, then placing some wooden boards on the surface will help to spread your weight and protect the soil structure. Many Irish gardeners are also increasingly taking a “no-dig” or “little-dig” approach to their plots, as a way of protecting soil integrity and minimising the challenges presented by climate change.

Even then, we’re sometimes faced with the challenges of a damaged soil through no fault of our own. For example, soil compaction is routinely found in new/ young gardens after the recent use of heavy machinery or where building works have been carried out without first taking preventative measures to protect the precious topsoil from damage. Any garden designer will vouch for the multitude of problems this causes, as well as the lack of interest shown by too many builders when it comes to avoiding it in the first place. In this case, protective measures that should be taken at the start of any build include minimising heavy traffic, generously fencing off established trees and shrubs to protect their root systems, and if required, temporarily carefully stripping and safely storing the topsoil from areas of the site or garden that will be disturbed by the build until the time comes to lay out beds and borders. In short, think of it as akin to baking the perfectly light and fluffy sponge cake. Handle this most precious of ingredients with deep respect throughout the process and your plants (and the planet) will thank you for it.

This week in the garden

Birds will soon start stripping the ripe berries from holly bushes, so earmark some branches for cutting in the next couple of weeks. Placed in a bucket of water in a cool, dark shed, they’ll stay perfectly fresh until needed for Christmas decorations.

If you’re already feeling starved of the seasonal beauty of home-grown cut flowers, then consider potting on some hyacinth, paperwhites or amaryllis/hippeastrum treated bulbs to grow on under cover in a cool, bright, frost -free but unheated spot, a process known as “indoor forcing”. Potted on this week, they’re likely to be in full flower for Christmas (bulb stockists include mrmiddleton.com).

Dates for your diary

Until Sunday, November 12th: National Botanic Gardens Glasnevin, Dublin, Crainn na hÉireann, an exhibition of more than 60 paintings produced over the past two years by members of the Irish Society of Botanical Artists as a celebration of the seasonal beauty of Ireland’s native trees. irishbotanicalartists.ie

Thursday, November 23rd, 8pm: Northridge House, St Luke’s Castle Road, Mahon, T12H970, Cork. On behalf of Cork Alpine Hardy Plant Society, a screening of the film Wildside: Story of a Garden, which tells the tale of Keith and Ros Wiley’s extraordinary and innovative garden in Devon, Wildside. All welcome, visitors €10.

Sunday, November 26th, and Sunday, December 3rd, 10am-1pm: The Grinding House, June Blake Garden, Tinode, Blessington, Co Wicklow, seasonal Christmas wreath-making workshops with garden writer and flower-farmer-florist Fionnuala Fallon. eventbrite.com/o/fionnuala-fallon-74563213293 or @theirishflowerfarmer to book tickets.