You’d think he’d get bored. For more than 40 years, John McCracken has been producing nothing but plain, anonymous, geometrically shaped objects from plywood and fibreglass lacquered in a single colour, often black. There is no decoration or anything else to disturb these immaculate objects, so highly polished that you can see yourself in them. Most are not unlike the monolith that puts in an occasional appearance in 2001: A Space Odyssey. Yet, unlike that mysterious object, which seems to turn up whenever humanity is about to take some momentous step forward, the meaning of McCracken’s objects is entirely impenetrable.

You can currently see 15 of them in the Royal Botanic Garden at Inverleith House, where they benefit from their sylvan surroundings. The unremittingly man-made contrasts with nature; the geo­metric and artificial is sharply set off against the organic, seen through the windows. Many of the objects are virtually identical; all are distributed unequally between the rooms. Some are freestanding. Others lean against the walls. Most are black. Some are white, blue, red or yellow.

You can talk about the way these works are located on the border between painting and sculpture. You can think about them as examples of American West Coast cool (McCracken was born in California in 1934). You might more profitably recognise how much they rely on their location for whatever qualities they possess, reflecting the light that falls on them in these beautifully lit spaces. Yet I wonder at McCracken’s high boredom threshold.

The exhibitions devoted to present-day art in Edinburgh are varied, numerous and good. Artist Rooms (Scottish National Gallery of Modern Art, until Nov 8) has representative displays by the likes of Agnes Martin, Andy Warhol and Damien Hirst. The Enlightenments (various venues until Sept 27) is a confusing hotchpotch of individual pieces. There are abstract paintings by Callum Innes (Ingleby Gallery, until Sept 19), and there is John Bellany (Open Eye Gallery, until Sept 1). The Wilson twins are showing a film and photographs at the Talbot Rice Gallery (until Sept 26). And then there’s Eva Hesse.

Hesse’s work, on show at the Fruitmarket Gallery, can be very touching, though this may well have more to do with the circumstances of her brief life than with the objects themselves. Her odd creations, many of them made from latex, papier-mâché, cheesecloth, varnish and rope, seem more like natural growths than works of art. Those that are not touched by sadness verge on the chilling. Born in Hamburg in 1936, she died in New York in 1970 of a brain tumour, at just 34. Her husband had recently left her. Her Jewish parents, having escaped from the Nazis, divorced when she was nine. Then her mother committed suicide. Though her career lasted just 10 years, Hesse established a formidable reputation. But what is it based on? Hesse exhibitions are still quite rare, so few of us have ever seen much of her work, other than as photographs. This is largely because there isn’t very much of it, and what there is is lent reluctantly because it doesn’t travel well and is a conservator’s nightmare. In fact, much of what we see wasn’t intended for exhibition. The objects were experiments, or, in the word coined for the show, “studiowork”. Most don’t look like work in progress, though. Each piece has a distinct aura. You wouldn’t be surprised if some blew away in the next draught, or if others suddenly sprouted or grew mould while you watched. With their viscous surfaces and attachments of rope or string, they’re a bit reminiscent of Beuys, although Beuys with taste.

When Hesse died in 1970, Alan Davie was already 50, and one of this country’s most admired painters. There’s no mystery about this. He was the British painter most like an abstract expressionist, and was even mentioned approvingly by art critics across the Atlantic. Yet Davie had never lived in America, and he didn’t visit until 1956; he had first been taken by Jackson Pollock’s work in Venice. Davie didn’t just love modern jazz, but followed its improvisatory methods when making his paintings.

He was hugely successful, with his bright, seemingly spontaneous compositions and their primitive, magical imagery. But we somehow almost lost sight of him. His age (he’s 90 next year) and nationality (he’s a Scot, born near Edinburgh) explain what he's doing here now, although the venue ought to have been grander. The Dovecot is too small for anything more than a partial retrospective, and the show left me wanting more, especially because it consists not only of paintings, but also of tapestries, rugs, jewellery, documentary material and pieces from Davie’s distinguished collection of tribal art. Of all the smaller shows now on in Edinburgh, I enjoyed this one the most.

John McCracken, Inverleith House, Royal Botanic Garden, until Oct 11; Eva Hesse, Fruitmarket Gallery, until Oct 25; The Colourful World of Alan Davie, Dovecot Studios, until Sept 26