Giant floral birthday candles and lilac flames.

I planted tree dahlias (Dahlia imperialis, a tuber from Mexico, Central America and Colombia) in a circle a few years ago and the effect, come flowering, is like some weird magnified candle-and-potassium flame effect (to my eyes, at least), just in time for J’s birthday. It’s the last day of autumn now but these lilac flowers, beaming at 5m high (it can reach 10m), towering over half the garden, are bringing gentle but somehow bright colour into the cool, often damp garden.

`We’re here – the show’s arrived!’

But I reckon too many people plant one tuber amongst other, relatively dwarf, perennials and shrubs, so the effect is of one triffid lurking in a corner of the garden, horribly out of scale. So please, plant them near trees, or if you are lucky enough to have a country garden like I do, then plant a few. Or none.

Of course the tree dahlias are in my part of the garden so wishing J Happy Birthday with them is quite a conceit.

More appropriate for my conservationist were the many trigger plants (Stylidium, why were some flowering so early?) and `dippy’s’ (as we call Diplarrena moraea) that I gave him.

Why are these little spring wildflowers blooming now - in late autumn?

Before we built our cedar cottage the paddock below - almost a wildflower meadow - was like a tapestry in spring, studded with jewels: spires of pink trigger plants, and white flag (or `dippy’s’) gave an effect like many pure white butterflies hovering at nearly a metre high. The area - which unromantically had to house our septic runs - now is our orchard but we are slowly returning these wildflowers to their home, in the grass, amongst the trees.

In areas of bush around our garden we delight in these blooms and other indigenous plants. But never do the trigger plants bloom in autumn. I bought these from local indigenous nursery Birdsland. So...was it the poly house? The sunshine? The frequent watering? It's hard to know.

One of those many anomalies to just enjoy.

Jill Weatherhead is horticulturist, writer, garden designer and principal at Jill Weatherhead Garden Design who lives in the Dandenong Ranges east of Melbourne, and works throughout Victoria (www.jillweatherheadgardendesign.com.au)