After the builders have left, first sort the soil in your new garden

In last week’s column, I wrote about the many challenges of designing and planting a small garden. But what of the special challenges presented by a brand-new garden belonging to a brand-new property, as in the sort of virgin space that has never been gardened? In particular, how does any novice gardener go about performing that magical trick of transforming the dirty, grey soil of what was up until recently a busy building site into the kind of crumbly, chocolate-coloured growing medium in which plants will happily grow?

Well, let’s start with the bad news, which is that your brand-new garden’s soil has almost certainly been compacted by the traffic of heavy building machinery and intensive footfall, as well as bulky building materials being stored on site. Not only is such a soil starved of oxygen but its delicate balance of micro-organisms – crucial to its health and fertility – is badly out of whack. How to tell if it’s compacted? Typical signs include poor drainage and pooling of water, stunted or yellowed growth (most obvious in lawns) and a caked or “panned” cracked surface in summer. The only plants happy to make a home in it will be those few weeds stubborn enough to have withstood the regular tramp of builders’ boots and with root systems resilient enough to successfully penetrate it.

This might sound grim, but the good news is even the most badly compacted soils can be remedied with the addition of plentiful amounts of organic matter plus a good sprinkle of powdered seaweed (available from good garden centres) and some initial judicious digging. I say judicious because while too much digging is bad for any soil, the impermeable “pan” of a compacted soil does need to be broken up in order to begin the process of repairing it.

If it is very badly compacted, you will need to use a pickaxe or a mattock to do this. Otherwise, a sturdy garden fork should suffice. Either way, only ever dig during dry weather to avoid causing yet more damage. The aim is to aerate the soil to a depth of no more than 15-20cm, removing any weeds, builder’s waste/ rubble or large stones uncovered in the process, before mulching it generously with well-rotted farmyard manure or homemade compost or a soil-enricher like Envirogrind (available to order countrywide from quickcrop.ie). Don’t bother digging this in, as Mother Nature (in the shape of earthworms) will do it for you.

In some cases, the topsoil in a new garden is no such thing but instead a nutrient-poor subsoil (the layer of pale soil typically found beneath topsoil), which has been exposed by earthmoving operations as a result of construction works. If this is true of your garden, then along with the use of regular, generous organic mulches as discussed above, there are a couple of other options to consider. One – an expensive one – is to import some good quality topsoil. But be mindful of the potential problems of altering existing soil levels, especially when it comes to drains, manholes, garden structures and building’s damp courses. To avoid the risk of getting poor quality topsoil infested with perennial weed root fragments, source screened topsoil from a reputable supplier such as your local garden centre. For Dublin gardeners, I also heartily recommend the Pro-Grow Topsoil Mix from Dublin-based Landscape Depot.

Another solution is to create raised beds filled with imported topsoil, but again, be mindful of affecting existing levels/structures as mentioned above. If in any doubt, employ the services of a professional landscaper to build these for you (ask your local garden centre for recommendations). Alternatively, the excellent Sligo-based Quick Crop (quickcrop.ie), will supply raised timber beds and the top soil to fill them for delivery countrywide.

Alternatively, you could see it as an exciting opportunity to create a pollinator-friendly, perennial meadow filled with the kind of plants that will thrive in this kind of nutrient-poor soil. If that sounds intriguing, then see pictorial meadows.co.uk, whose range of seed-mixes includes some specifically designed for low-fertility soils including dry, rubble-filled ones. Alternatively, Laois-based Sandro Cafolla supplies a range of native wildflower mixes (see wildflowers.ie) that are eminently suitable for low-fertility soils including damp ones.

Which brings me to another all-important piece of advice when it comes to any new garden’s soil, and one that I touched on last week, which is to choose those plants that suit it best. Is it, for example, a heavy, poor-draining clay? Then concentrate on plants that like this soil, such as species of berberis, spiraea, cotinus, Magnolia x soulangeana, aconitum, phlox, rudbeckia, actaea, ajuga and astilbe. Sandy and free-draining? Try Sophora, arbutus, artemisia, brachyglottis, pittosporum, cytisus, cistus, phlomis, dierama, romneya , tulips and perovskia. For more detailed suggestions, see rhs.org.uk . In other words, the right plants for the right soil and in the right place – make that your mantra and you won’t go far wrong.

This week in the garden:

· Sow seed of micro-leaves (tiny, edible, seedlings that you harvest within a few weeks of their germination) into small pots or seed-trays placed on a bright window-sill indoors. These can be used to liven up winter salads, stir-fries, sandwiches, soups and even cocktails and puddings. You can use any leftover seed packets of herbs or salad leaves approaching their sow-by date or order seed mixes from specialist seed suppliers such as Brown Envelope Seeds (brownenvelopeseeds.com), Seedaholic (seedaholic.com) and Nicky's Garden (nickys-nursery.co.uk)

· Continue to home-save the seeds of many different plants; the dry, mild weather of recent months has resulted in such a bumper crop of ripe seed that it would be a shame to waste it. See my online column of October 1st for details on how best to do this.

· Leaf fall heralds the beginning of the bare-root season and is a great opportunity to plant trees and shrubs, including many fruit-bearing kinds. Bare-root specimens are also significantly cheaper than their pot-grown equivalents, so if you are starting a new garden, it is a really economical way to acquire some fantastic plants.

Dates For Your Diary: Wednesday, November 9th, at 8pm, Kill o' the Grange Parish Centre, Kill Lane, Dublin, James McConnell and John Curran, RTÉ Super Garden winners and Bloom medallists, will give a talk on behalf of South County Dublin Horticultural Society entitled Gardens with Atmosphere. Visitors €5; Friday, November 11th (6.45pm-9pm), Hunting Brook Gardens, near Blessington, Co Wicklow: Gardening on the Edge is the topic of this month's supper club evening at Hunting Brook Gardens, where over the course of a tasty, home-cooked vegetarian meal, its owner, plantsman, lecturer and general all-round gardening guru Jimi Blake, will be talking about the plants he uses to achieve his distinctive style (€35, pre-booking essential, see huntingbrook.com); Kiltrea Bridge Pottery, Enniscorthy, Co Wexford, pre-Christmas sale finishes continues today, 11am-5pm, and tomorrow, Sunday, 2-5pm, and includes a range of charming handmade garden pots and rhubarb forcers. See kiltreapottery.com