MY WORKPLACE is a walled garden in Liverpool: a hectic place, where horticultural students and volunteers all need encouragement and direction. It is all too easy to get caught up in the busyness and not notice the beauty of the place.

Sometimes, though, as I rush from one area to another, a sight in one of the borders stops me in my tracks, and it is usually the juxtaposition of two plants which works this magic. Pairing plants that set each other off to perfection is part of the artistry in gardening, and, when done well, it raises a garden above being a mere collection of plants.

So, what makes an effective combination? It is all about having the right amount of contrast. Two cow parsley relatives next to one another, a white wild carrot (Daucus carota) and bishop’s flower (Ammi majus) say, while both beautiful and differing to some extent in leaf colour, texture, and flower size, are too similar.

There need to be some connection and some contrast. When two plants “just look right” together, the link often stems from nature, when the plants in question are showier versions of wild cousins that co-exist in a plant community. Hence, either the milk parsley or the bishop’s flower could sit easily alongside the elegant spires of the white rosebay willowherb, Chamaenerion angustifolium “Album”.

The connection may be made by the colour of one plant part, perhaps its stamens, matching by a different element: the petals say, of the neighbour. Or the link could be to do with flower structure. In my garden, at the moment, the bold vertical spikes of a white bellflower (Campanula persicifolia) is surrounded by a haze of delicate Bowman’s root (Gillenia trifoliata). The different texture of the two species is balanced by each having five petals as well as a colour match.

A garden based on one plant-pairing would, indeed, be minimalist. Each member of the pair will usually have other neighbours. So, effective planting schemes are loosely woven tapestries, and the conversations between plants stop only with the full stop of a gate or wall or other divider.

If this sounds daunting, the best way to exercise it better in our own outdoor spaces is to visit other people’s gardens and to look at what works — and ask yourself why it works.The National Garden Scheme (NGS) website or handbook makes it easy to find a special garden to visit in England or Wales. This British institution, founded in 1927, has raised £25 million for nursing charities in the past ten years alone.

Garden owners will be on hand to help identify and give care advice for any plants that catch your eye. There may be a plant stall, but, even if you don’t come away with an actual specimen, make notes, take photographs, and resolve to recreate a particular grouping.

I remember admiring a long herbaceous border in a private Cheshire garden open for NGS. While I was analysing it, the owner approached, asking, “Do you like my Scooby Doo border?” The same segment of planting was repeated several times along its length, like the backdrop during chase scenes in certain animations. This effective design ploy has stayed with me.

www.ngs.org.uk