Let your garden be a bonanza for butterflies

Late-summer flowers like marigolds, lavender, phlox and daisies are all a valuable source of food for butterflies

A Peacock butterfly feeding on the nectar-rich flowers of oregano growing in Ashtown Walled Garden in the Phoenix Park. Photograph: Richard Johnston

The recent drought may not have been kind to many Irish gardens, but oh what a wonderful summer it’s been for seeing butterflies on the wing. In recent weeks, I’ve spotted all sorts of different species flitting amongst the flowers – from the Tortoiseshell, the Red Admiral and the large and brilliantly colourful Peacock to a host of more subtly coloured Irish butterflies including the dainty Common Blue, the Speckled Wood, the Meadow Brown and even the Grayling.

Of course, July-September is one of the peak times of the year to see these exquisite creatures (the other is late May), but the warm, sunny weather has also helped. Most butterflies, you see, are reluctant to take flight unless weather conditions are favourable – that means a dry, bright day with temperatures above 13ºC.

Dry, warm weather is also necessary for these exquisite insects to successfully emerge from their protective chrysalises and for their delicate wings to dry in preparation for flight, which in turn allows them to go in search of a mate as well as food. It’s also necessary for ‘butterfly basking’– unable to self-regulate their body temperatures, butterflies stretch their wings out wide in bright sunshine as a way of absorbing its heat and warming themselves up.

All of which might lead one to reasonably conclude that unusually hot, dry summers like this one are good news for Ireland's butterflies. But it's not that simple. Instead, the prolonged dry conditions of recent months pose a considerable threat to the country's already dwindling butterfly population, which has declined by 12 per cent over the last decade, according to Dr Tomás Murray, a senior ecologist with Biodiversity Ireland.


The reason for this is the damage that drought has caused to their vulnerable habitats, in particular to the different species of wild plants that these magical creatures rely upon for the purpose of egg-laying as well as for food for their young caterpillars.

Common nettle

An example is the common nettle, a common garden weed and the sole larval food plant of the Red Admiral, which lays its grey-green eggs singly on the upper surface of its leaves. The problem is that the common nettle is a wild plant that flourishes in cool, rich, damp soil; it hasn’t liked this exceptionally dry, hot Irish summer one little bit, so much so that the leaves of nettles growing in some of Ireland’s most drought-stricken gardens have slowly turned to a brown crisp. Most of these impressively resilient perennial wild plants aren’t dead. Instead, they’re just conserving their energy until growing conditions improve. But it does mean there are fewer suitable host nettle plants available at a time when Red Admiral butterflies need them for the important business of egg-laying.

Even if the butterflies are successful in finding suitable host plants, the worry is there won’t be enough luscious nettle leaves left for the emerging caterpillars to feed on. The very same is true of other kinds of Irish wild plants that provide a habitat for the larval stage of some of our loveliest butterflies, from wild grasses to common wildflowers such as sheep’s-bit, thistle, dock, knapweed and lady’s bedstraw.

So what can we, as gardeners, do to help? The answer is plenty. Make a start by putting away your garden strimmers and leaving the wilder areas of your garden untouched until at least late autumn, by which time this summer’s final generation of butterflies will have either emerged and migrated to warmer countries or found a place to safely overwinter.

But, as Dr Tomás Murray points out, it's not just actual butterflies which need a safe place to hibernate; some butterfly species also overwinter in Ireland as eggs, or as caterpillars or as chrysalises, so the more patches of wild you allow to exist along the margins of your garden, then the more you can help.

For the same reason, avoid using garden insecticides or herbicides, which inevitably cause long-term harm to Ireland’s butterfly populations as well as to the plants they depend upon to provide a suitable habitat for their eggs and larvae.

While wild species of plants are crucial in terms of providing butterflies with suitable habitats, many popular late summer/early autumn flowering garden plants are very attractive to them as a valuable source of food, allowing us gardeners to enjoy the sight of these extraordinary wild creatures close-up.

Top of Biodiversity Ireland's list are varieties of sedum/ hylotelephium, commonly known as stonecrop or ice-plants, whose nectar-rich flowers are irresistible to many species. Also lavender (Lavandula), Michaelmas daisies (Aster), phlox and annual French marigolds (Calendula).

Invasive qualities

Although Murray cautions against growing the shrubby, long-flowering butterfly bush (Buddleja) because of its potentially invasive qualities, its large and decorative blooms are also marvellous for attracting large quantities of butterflies into any garden.

Better-behaved, sterile forms (varieties that don't produce viable seed) are now available, such as the ultra-compact Buddleja x alternifolia 'Unique', while deadheading any of the many decorative but fertile varieties of supremely butterfly-friendly plants such as the violet-purple B. davidii  'Black Knight' and the pink-orange-lilac flowering B. x weyeriana 'Bicolor' will also prevent them from setting viable seed.

Other late summer/early autumn-flowering butterfly-friendly plants I'd add to his list include varieties of scabious (Scabiosa), marjoram, eupatorium, monarda, salvia, gaura, actaea, echinops, single-flowered dahlias, agastache, helenium, linaria, rudbeckia, nicotiana and ammi.

Finally, if you'd like to learn more about these marvellous flying creatures, check out the website (biodiversityireland.ie) of Biodiversity Ireland, which includes a host of very useful resources, including a downloadable 'Crash Course in Butterfly Identification', an illustrated 'Butterfly Identification' swatch perfect for nature walks (order online for €6) plus information on its Irish Butterfly Monitoring Scheme and its Butterfly Atlas 2021, both of which are co-ordinated by Dr Murray.

This week in the garden . . .

After this summer’s prolonged drought, the very welcome arrival of rain in many Irish gardens in recent weeks means that growth is slowly returning to normal levels for this time of year. That said, do go gently when it comes to cutting lawns as their root systems need sufficient time to properly recover from stress brought on by the recent drought. So keep your lawnmower’s blades at a high-ish setting and don’t mow too frequently. If your lawn is only a small one, it’s also worth giving it a liquid seaweed feed to help its speedy recovery.

Use a sharp secateurs to cut away the faded flower stems of late-spring and early-summer flowering perennials, which will greatly improve their appearance and in some cases will even encourage a second, smaller flush of flowers. Many of these types of plants, such as alchemilla, cranesbill/geraniums (not the bedding kinds which are properly known as pelargoniums), catmint and thalictrum will also benefit from a hard prune at this time of year, using a sharp garden shears or scissors to cut them back to just 5-7.5cm above the ground – avoid doing this if your garden was particularly badly hit by the recent drought as good soil moisture levels are required for the plants to put on a generous burst of new growth. Liquid feeding after pruning (again, only where soil moisture levels have recovered) will also help to encourage the production of fresh new growth.

In the kitchen garden or allotment, it’s important to keep regularly harvesting food crops such as French beans, runner beans, tomatoes, cucumbers and courgettes at this time of year to encourage the plants to continue to be productive for as long as possible. Again, regular liquid-feeding (every seven-10 days) with an organically approved liquid tomato feed or seaweed feed will also help greatly in terms of keeping plants healthy and productive for as long as possible.

Dates for your diary

Tomorrow (Sunday August 5th, 10am-5pm): Farmleigh Estate, Phoenix Park, Dublin, Farmleigh Autumn Plant Fair with specialist plants sales from members of ISNA (Irish Specialist Nurseries Association).

Thursday August 2nd-Friday August 24th: National Botanic Gardens, Glasnevin, Dublin 9, Devonian Plant Fossils': A window into the past, a joint exhibition by the National Botanic Gardens and the Natural History Museum showcasing the amazing 360-million-year-old plant fossils discovered in Kiltorcan Quarry, Co Kilkenny. This is the first time the collection will be on public display, see botanicgardens.ie.

Continuing until August 6th, Carlow Garden Festival, with talks by UK Gardener's World presenter and nurserywoman Carol Klein at Duckett's Grove Walled Garden in Carlow (tomorrow, Sunday 5th August). The same venue will also host a separate garden workshop by Klein as well as a period garden party, while on Monday, August 6th (from 12pm), Irish garden designer Elma Fenton will give a guided tour of Delta Sensory Gardens in Co Carlow and share her passion for garden design and plants, see carlowgardentrail.com for specific times/ various admission prices.