Barely a week on from the summer solstice and we’re already painfully past the annual peak of daylight length, a time of year that always causes me to catch my breath. Listen hard enough and you can almost hear the far-off grinding of gears, as nature switches its energies from vegetative growth to flowering, seed setting, and survival of the species.
That decline in day length, initially barely perceptible, accelerates as the months pass. It continues until the darkest days of the winter solstice, shrinking the number of daylight hours from 17 to just seven and a half, at which point it upends itself and the complex process is reversed.
But it’s not just the seasonal waxing and waning of natural light levels that has such a dramatic effect on plant growth and health. As gardeners, we learn that important differences in the intensity and quality of light can also be influenced by a myriad of modifiers other than the dance of stars and planets.
It could, for example, be the removal of a nearby tree that once cast shade for a part of the day, or perhaps the shadow of a new building changing a once-bright garden’s habitat, or even just a sustained period of cloudy weather, all things it took me decades to fully appreciate.
Plant shade-loving ferns, for example, into a bright, open, south-facing spot, and they will almost inevitably struggle to perform, perhaps even die. But plant them into a deep, loamy, humus-rich soil in a south-facing spot overshadowed for the hottest, brightest part of the day by a deciduous tree and they are likely to flourish.
Equally, plant a light-loving species – for example, pelargoniums – in a shady spot and they will unsurprisingly almost certainly give up the ghost.
But crucially, those same light-loving species can still struggle in a sunny, south- or west-facing location when weather conditions result in a sun-starved, cloudier-than-average Irish summer.
Understanding these subtle, ever fluctuating differences in the type of shade, or conversely lack of shade, is a challenge. It’s one made more difficult by that popular gardening term “shade loving”, an umbrella description that suggests there’s a one-size-fits-all solution when that’s simply not the case.
Many woodland species of plant, for example, have evolved to thrive in dappled shade along the edge of wooded areas. These kinds of plants typically flourish in the seasonal partial shade cast by deciduous and herbaceous species that aren’t in leaf all year round, and also require the sort of damp, fertile, humus-rich soils associated with such woodlands where decades of leaf litter have enriched the soil.
Give them the sort of deep, unyielding, year-round dry shade found along the north-facing foot of a high wall or building, and they’re going to be unhappy. Instead that role falls to a handful of ultra-resilient shade and drought-tolerant species (examples include Saxifraga stolonifera; Geranium macrorrhizum; Epimedium x rubrum; and Mahonia “Charity”).
Similarly, most gardeners know that east and north-facing aspects are classed as cool and shady, while south- and west-facing parts are typically classed as warm and bright. But it’s also important to bear in mind that light levels in a garden can and do change dramatically over a single day, as well as over years and decades.
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As trees, shrubs and hedging grow and mature, for example, they will inevitably transform what were once bright, open spaces into areas where light levels fluctuate hugely. This has consequences for any light-loving species planted in a garden’s youth, which can subsequently find themselves in what have become shady conditions not to their liking.
Consider the changing nature of shade cast by an evergreen hedge, both as it matures and as the sun traverses the sky. In early morning, that shade – a shadow cast by the angle and position of the sun, and which also lengthens and stretches as the hedge itself grows and matures – lies to the west of the hedge. By noon, to the north. But by evening it’s to the east. The taller the hedge, the greater the extent of that same shadow, which is also at its most extended in early morning just after the sun rises, and then again in late evening as the sun starts to set.
In a world where a plethora of gardening advice is freely available to us all on the internet, key regional variations in the quality of light can also be easily overlooked. Full sun in a cool Irish garden is in no way equivalent, for example, to full sun in a Texan garden, or even one in the drier, sunny corners of southwest England. Such is the very different quality and intensity of that sunlight that plants that might quickly shrivel to a crisp in those hotter, brighter climes will grow quite happily in a sunny spot here in Ireland, just so long as the soil remains cool and damp.
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Conversely, there are light-loving species – for example, zinnia or celosia – that can be grown easily in otherparts of Europe and the US, but struggle to flourish in an Irish garden, even when given the brightest, sunniest spot. Heat aside, we just can’t reliably give them the consistent levels of intense sunlight they relish.
The same goes for certain kinds of fruit and vegetables, including some slow-to-ripen varieties of beefsteak tomatoes; aubergine; peppers; kiwi; and melon. It’s not only heat that these need to truly flourish, but also plenty of long, bright, sunny summer days, never guaranteed here in this northwesterly corner of Europe
On the plus side are those many species that thrive in our temperate, maritime Irish climate, from shade-tolerant ornamentals such as hosta, primula, fatsia, foxgloves, aquilegia, tellima, hydrangea, and narcissus, to many kinds of edibles including rhubarb, lettuce, beetroot, salad leaves, brassicas, peas, currants and apple trees.
The lesson to be learned? Just like an artist or a photographer, becoming intimately acquainted with the ever-shifting quality, intensity and direction of light is key to the art of good gardening and part of the secret to unlocking the potential magic of our outdoor spaces.
This week in the garden
The larvae of certain species (examples include box caterpillar, carrot fly, gooseberry sawfly and cabbage white butterfly) can quickly cause a lot of damage to plants at this time of year, weakening or even killing them. A combination of measures such as netting and handpicking is the most planet-friendly approach but isn’t always feasible. In the case of bad infestations, biological controls such as the naturally occurring Bacillus thuringiensis or nematodes such as Nemasys Natural Fruit and Veg Protection can be very effective (stockists include fruithillfarm.com and mrmiddleton.com)
Offer late summer-flowering perennials and tall-growing vegetables some sort of sturdy support to protect them against wind damage, bearing in mind the eventual size of the plants when mature.
Dates for your diary
Delgany and District Horticultural Society Rose Show - Saturday, June 28th, St Patrick’s National School, Greystones, Co Wicklow. All entries very welcome. To submit an entry, please email ddhs.showentries@gmail.com by Thursday June 25th.
Specialist Plant Fair Weekend, Mount Stewart Gardens, Co Down - Saturday June 27th and Sunday June 28th (10am-6pm). nationaltrust.org.uk
