How rain can be great for your garden

I am bored of rain. Fed up with cloudy days. Sick of the grey drip-drip-drip of this cool, showery, sun-starved, stormy summer, and the monotony of a weather forecast that only predicts more of the same. But even so, I’m forced to admit that the silver lining to what’s been a very sodden growing season is that many of our most beautiful, late summer-autumn flowering garden perennials and shrubs are loving the biblical quantities of rainfall in recent months, a high note to what’s otherwise been a forgettable year.

A large part of the reason for their contentment is that these plants thrive in the kinds of growing conditions often described in gardening books, as well as gardening columns such as this one, as “moist but free-draining”. The latter is a description that’s bewildering to new gardeners, a frustrating, bamboozling contradiction in horticultural terms that needs explanation. How, you might reasonably wonder, can a soil be both moist and free-draining at the same time? Wet and yet dry? The answer is the kind of soil where stagnant rainwater doesn’t regularly pool or puddle around the plant’s roots to create anaerobic growing conditions but instead drains away quickly, albeit not to the point where the soil is ever parched and thirsty.

In many Irish gardens the soil is too heavy and abundant in tiny clay particles to be naturally free-draining. Photograph: iStock

Of course, not every Irish garden or allotment naturally provides these kinds of growing conditions. In many, for example, the existing soil is too heavy and abundant in tiny clay particles to be naturally free-draining. In this case the ground will be nutrient-rich yet very slow to dry out in spring, but then inclined to bake hard and to crack in a warm, dry summer. Alternatively, in an especially wet summer such as this one, clay soils can be sticky, slow to drain after heavy rainfall and very vulnerable to damage through compaction and “caking” if walked on or dug.

The solution? The best way to improve a wet, heavy clay soil’s structure and its ability to drain freely is with the regular addition of plenty of horticultural grit (but not builder’s sand, which will only compound the problem), and lots and lots of bulky organic matter in the shape of home-made garden compost and/or well-rotted manure added as mulches in spring and autumn. A no-dig approach, as popularised by the British gardener Charles Dowding, will also help.

However, where growing conditions are consistently poor regarding drainage, the best and easiest solution to a heavy clay soil is a raised bed. A small change of level of as little as 25cm – the soil can be simply banked up or mounded if a retaining edge of blocks, wood or stone is too costly an option – will make all the difference regarding drainage, dramatically boosting plant health and vigour as well as resilience in the face of extreme rainfall events. If the budget allows, using as much of a good-quality imported top soil as you can afford will also help a lot (recommended suppliers include landscapedepot.ie).

Home-made compost is a great start but sadly there’s rarely enough in the average domestic bin to meet the average garden’s needs

Conversely, other Irish gardens and allotments have the kinds of hungry soils that are so light and so free-draining that they typically struggle to retain moisture and nutrients. These soils warm up quickly in spring, but plants often begin to run out of steam in midsummer as the ground starts to dry out. Again, in this case the very best way to improve growing conditions and the soil’s ability to retain moisture and nutrients is with the addition of plenty of well-rotted organic matter in spring and/or autumn.

Which brings me to the perennial problem of sourcing a sufficient, affordable quantity of good-quality, well-rotted organic matter to amend a garden or allotment’s soil. The painful truth is that this can be challenging and expensive, especially if you live in a very built-up urban area where there’s no easy access to well-rotted farmyard manure or foraged seaweed. Home-made compost is a great start but sadly there’s rarely enough in the average domestic bin to meet the average garden’s needs. The same goes for vermicompost (worm casts) and Bokashi compost.

Home-made compost is a great start. Photograph: Alamy/PA

In this case part of the solution to improving a soil’s ability to withstand sustained heavy rainfall and help it to earn that golden title of “moist and well-drained” lies in the use of green manures, many varieties of which can be sown in the coming weeks. Garden-generated organic mulches such as lawn clippings, very finely chopped hedge trimmings, straw and leaf mould are also very beneficial. So is the use of high-quality Irish organic manure and organic manufactured mulches (see mulch.ie, enrich.ie, envirogardenndhome.com and geeup.ie), as is the French-Canadian technique known as BRF or RCW championed by the Laois-based organic gardener Tanguy de Toulgoët of Dunmore Country School near Durrow (dunmorecountryschool.ie). It was originally developed by Edgar Guay in the 1970s to help Quebec foresters, and replicates the conditions found in natural woodlands as a way of dramatically regenerating soil health and fertility.

Another part of the solution is the use of soil enrichers that boost soil health and microbial activity such as Soil Renew (soilrenewireland.ie), Supersoil (supersoilglobal.com) and hexafrass (hexafly.com). Yet another is the addition of the magical ingredient known as biochar (biocharireland.ie), a type of charcoal that helps sequester carbon and dramatically increases water and nutrient availability. Finally, the addition of gypsum will also improve the texture of clay soil and its ability to quickly drain heavy downpours. If it’s a very acid clay soil, adding some garden lime in late autumn will also help to raise the pH and improve the availability of certain nutrients.

All of the above will also help the soils in our gardens and allotments to much better tolerate periods of drought, a threat that feels very far away at the moment given this strange summer of record rainfall. But weather extremes caused by climate change will inevitably eventually send the pendulum swinging in the opposite direction. Either way, deluges or drought, “moist but well-drained” is the goal to aim for, the gold standard of soil that allows many of our loveliest garden plants to flourish.

Lift the garlic bulbs gently using a garden fork to avoid damaging them

Garlic is usually ready to harvest from the kitchen garden or allotment at this time of year. Signs that the bulbs have fattened up and hardened off include yellowing-browning of the leaves, which should still be upright at harvest time to avoid problems with rotting during storage. Lift the bulbs gently using a garden fork to avoid damaging them, shake off any excess soil and then place them in a dry, well-ventilated space indoors for a few weeks to dry off.

Sow green or “living” manures to bolster soil health, structure and fertility and protect them from erosion and leaching of nutrients. Varieties suitable for sowing over the coming weeks include field beans, red and white clover, mustard, winter vetch, phacelia and buckwheat. Depending on the variety used, these can be left in the soil from a few months to up to a year before being cut down and left as a mulch or dug back into the soil. See rhs.org.uk for detailed advice and mrmiddleton.com, quickcrop.ie and fruithillfarm.com for suppliers.

Tomorrow, Sunday August 27th (9.30am-5pm): The final Dublin-based ISNA Plant Fair of the year takes place at Airfield House and Gardens, Dundrum, Dublin 14, with stalls from more than 20 ISNA specialist nurseries. airfield.ie

Tuesday, September 5th: The Irish Dahlia Society National Show takes place at Ballyknockan Farm, Wexford Y21-A526. All potential exhibitors should please email their entries to Pat Thornton at [email protected] or Trevor Stevenson at [email protected] on or before Saturday, September 2nd.

Tuesday, September 26th, 7pm: White Sands Hotel, Portmarnock, Co Dublin, D13 W7X2, an illustrated talk by the renowned American plantsman, nurseryman and author Dan Hinkley on behalf of Howth & Sutton Horticultural Society. This ticketed event (€15) must be reserved/booked in advance. hshs.ie

Dan Hinkley will also be one of the guest speakers at Kells Bay Gardens’ Southern Symposium (Friday-Sunday, September 29th-October 1st) along with Seamus O’Brien, Bleddyn and Sue Wynne-Jones, Jack Aldridge and Ken Cox. Reserve tickets at kellsgardens.ie