There is a specific day in the calendar year that divides the two halves, and its significance as a major horticultural turning point is well known to experienced gardeners. Known as the summer solstice in the Northern Hemisphere, this day occurred yesterday, June 21st, the longest day and shortest night of the year, when the North Pole was at its greatest tilt towards the Sun.
While in humans the circadian clock has a regulating effect on mood, health, well-being, performance, attention, cognition and sleep patterns, the circadian clock in plants also responds to natural light in a myriad of complex ways. Longer days typically promote the process of photosynthesis and vegetative growth in the form of the production of roots, stems and leaves. In contrast, shorter days and longer nights typically progressively slow down the above processes and plants turn their attention to flowering, fruiting and seed formation in preparation for autumn and winter.
After the summer solstice, the pace and pattern of growth in our gardens and plots slows and changes, which is already evident in July, when the freshness, youth and vigorous energy of early summer is replaced by something more gentle.
This change can be seen in our parks, hedgerows, woodlands and even in the wild, as evidenced by a series of recent international scientific studies.
A paper published in Nature Plants earlier this year investigated the remarkably coordinated response of beech populations across Europe to the occurrence of the Northern Hemisphere summer solstice, vividly describing the solstice as a “starting gun” or “signal from above”, showing that beech trees are remarkably sensitive to the summer solstice, regardless of where on the continent they are growing.
The researchers were also surprised to find that a few minutes less daylight in the days immediately following the summer solstice can dramatically change the tree growth response to subsequent weather patterns, especially temperature. This could play a key role in synchronizing seed production and help explain the mystery of so-called “mast years,” when beech trees produce large amounts of seeds.
So what does all of the above mean for Irish gardeners? It means that if you have young plants or hardy seedlings potted in trays or liners still waiting to take root in the ground, you need to take action now if you want them to grow well. And if you've been putting off sowing seeds for your cold-hardy biennials and perennials, hurry up.
The same is true for softwood cuttings that root quickly at this time of year because they are full of plant hormones; not for semi-hardwood cuttings taken later in the season, nor for hardwood cuttings taken in the fall. This means that the bubbly, floating, youthful beauty of an Irish garden in early summer is now a year old. I always judge this by the parsley flowers dying from the hedges and the lupines going to seed.
As with European beech trees, this also means you can gradually turn your attention away from the busy hustle and bustle of late spring and early summer sowing and planting, and focus on tasks that are a natural part of a late summer garden.
This includes harvesting home-grown fruits and vegetables, deadheading and applying liquid fertilizer to prolong the life of flowers, weeding and plowing flower beds and flowerbeds to promote healthy plant growth, and watering plants as needed, always respecting plants as a precious and finite resource. It also includes home seed saving, one of the most important and rewarding late-summer garden chores.
Freed from the rush of gardening in spring and early summer, you can take the time to literally and figuratively smell the roses. Or, if you don't have roses planted but wish you did, carefully write down what you'd like to have in your garden this time next year.
[ What every Irish garden needs: exceptional but hardy and resilient plants ]
Or better yet, be inspired by clever design ideas and stunning plant combinations by visiting some of Ireland's great gardens which will be open to the public this summer, many of which can be found in Kilkenny-based garden writer Shirley Lanigan's excellent new book, The Open Gardens of Ireland, published this month by Butterslip Press and available from most good bookshops and garden centres in Ireland.
Covering a total of 375 Irish gardens, from small modern city lots to centuries-old castles and vast historic estates of grand country houses, this comprehensive guide beautifully encapsulates Lanigan's long-standing interest in the very personal art and craft of gardening. It also serves as a powerful reminder of the value of collective consciousness and the wealth of knowledge it contains. As the late, great garden designer and author Russell Page wrote in his classic book, The Education of a Gardener, “I have never seen a garden from which I did not learn something, and rarely have I met a gardener who did not help me in some way.”
Garden of the Week
Unstable weather and cool nighttime temperatures are tough on heat-loving summer bedding plants, which usually need plenty of warmth and sunshine to grow quickly. Until conditions improve later in the month, regularly deadhead and fertilize plants, and protect them from slug damage. If potted plants are suffering, try temporarily moving them closer to a south- or west-facing house wall to provide a little extra warmth and protection.
Aphids often appear at this time of year on the tips of tender green plant shoots, and although this can be a worry for gardeners, if you wait too long they will be eaten by predators such as ladybugs, ground beetles, earwigs, hoverflies and parasitic wasps. Alternatively, you can try crushing them between your finger and thumb or rinsing them off under a fine stream of water.
Date to write in diary
The Tullynally Castle Plant Fair takes place today, Saturday 22nd June (11am-5pm) in Castlepollard, Co Westmeath. For more details visit tullynallycastle.ie
A wide range of plants, vegetables, sweet peas and roses will be on display at the Delgany & District Horticultural Society Rose Show, St Patrick's Primary School, Church Road, Greystones, Co Wicklow, on Saturday 29th June (3pm-5pm). New members and exhibitors are warmly welcomed, please contact ddhs.showentries@gmail.com.
