Mammy, daddy and the kids: the “natural primary and fundamental unit group of society”, according to the Constitution. What could be simpler? Yet if you were to judge from the classic Irish plays of the 20th century, nothing could be more elusive. This is a centre that cannot hold.

It is very rare to see a major play with two parents and their children. Christy Mahon has no mother and "kills" his father. Juno and her Paycock are deeply sundered – Seán O'Casey's conclusion is that it is better to have two mothers rather than a ma and da. Teresa Deevy's Katie Roche and John B Keane's Sive are the children of dead single mothers. Hugh Leonard's autobiographical protagonist in Da is adopted. Mothers are almost always aching absences in Brian Friel's plays. The mother is only glancingly referred to in Tom Murphy's A Whistle in the Dark; in Bailegangaire the parents are completely removed, and the central relationship is between grandmother and granddaughters. (One could, of course, push this back further into the 18th and 19th centuries, with all those orphans and wards in Sheridan, Shaw and Wilde.)

So Irish theatre has long struggled with the nuclear family that is supposed to be the heart and soul of Irish culture. One might go so far as to suggest that there is just one great Irish play that has a "natural" mother, father and children on stage together. And that's Eugene O'Neill's Long Day's Journey into Night, in which the Tyrones really do make the Simpsons look like the Waltons.

All of which suggests that the failure of Frank McGuinness's The Hanging Gardens, at the Abbey, is not entirely surprising. McGuinness attempts what is, in Irish theatre, the highly unusual feat of creating a convincing nuclear family on stage. Unlike in Friel's Aristocrats, which forms a rough template for The Hanging Gardens, the play has both a father and a mother: the novelist Sam Grant, now declining into dementia, and his wife, Jane, an obsessive gardener and author of lucrative how-to-garden books. And we have their three grown-up children: Charlie, who has never left; Maurice, who is gay and troubled; and Rachel, who has returned to have the baby she hopes will give meaning to her life. The play's primary job is to convince us that these people do indeed form a familial unit. But it never really does that.

In part this is because McGuinness elaborates before he establishes. He creates a highly convoluted metaphorical structure, drawing on the imagery of Babylon in the Book of Revelations and on the myth of the hanging gardens that were one of the wonders of the ancient world. In a brilliantly arresting prologue, Niall Buggy’s Sam sits in the pouring rain in the garden intoning, “Fetch me the moon shining on Babylon.” The house itself is called (somewhat improbably for Buncrana) Babylon. The conjuring of the biblical invocation of the ancient city as “a dwelling place for demons / a haunt for every unclean spirit” establishes a sense of high significance and epic doom.

But this grand metaphorical edifice sits on very narrow and shaky ground. The high tone might be sustainable if the Grants worked as a unit. But they don’t. The play’s highlights are all in the sparky relationship between the waspish, overbearing and manipulative Sam and the angry and angular Jane. The second of the play’s five long scenes is played out entirely between the excellent Buggy and Barbara Brennan’s Jane and shows McGuinness at his best: humane and vivid with just the right seasoning of dark comedy and surreal oddness. It feels, in retrospect, as if this is where the play really lies: in this tangled, exasperated but enduring relationship.

The problem is that it tries to create a larger unit with the three grown-up children. They are sketchily conceived. Charlie, in an angry outburst, refers to himself as the “donkey” and to his siblings as “the whore and the queer”. It is, of course, a set of outrageous caricatures, but the characters themselves do not extend as far beyond them as they should. There is too little telling detail in the writing even for actors as talented as Cathy Belton, Declan Conlon and Marty Rea to build on.

The play is, moreover, unable to imagine the relationships of each of the three with their parents. This is true even in the most basic, spatial sense. How do these people occupy the same space? The answer is very awkwardly indeed. The typical scene is an encounter between one of the parents (usually Sam) and one of the children, with one of the others hovering conveniently at the back of the stage. Entrances are often managed as if this were a radio play and we could not see the action: “Your father’s coming?” “No, it’s Charlie.” Even the structuring of time – the action unfolds in what should be the elegant frame of a single day – becomes strained: the third scene begins just after lunch, but half an hour later it has become “early evening”, and Jane remarks that “there’s still light”.

This kind of discomfort is unusual in a playwright as accomplished as McGuinness. The strain is telling: there is nothing, in the Irish theatre, at all natural about the nuclear family. It is a strange and awkward thing, and playwrights approach it at their peril.

fotoole@irishtimes.com